61 posts · 21,305 views
Undergratuate hoping to someday study cell biology and development of various unicellular protists. Currently working on plant development, as well as exploring some evolution of biological, as well as cultural and linguistic, organisms as a hobby on the side. Considers public outreach of science to be crucial to both research funding and research progress itself, as teaching and learning are highly dependent on one another. Hopes to improve own communication skills via blogging. Wonders why she is referring to self in third person...
Skeptic Wonder
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- August 2, 2010
- 10:59 PM
- 66 views
Sunday Protist – Nematode-hunting amoebae: Theratromyxa
by Psi Wavefunction in Skeptic Wonder
A couple posts ago we saw how ecological relationships may refuse to obey the laws of their kingdoms: protists can hunt crustaceans. Protists can also farm bacteria, animals can parasitise unicellular protists, plants can parasitise fungi, fungi can hunt animals, animals can steal plastids and photosynthesise, as well as steal algae for their embryos, fungi parasitise protists, and perhaps plants may even feast on the occasional bacterium or two (though that's yet to be confirmed). It seems neither the organisms in question nor evolution itself received the memo wherein "plants photosynthesise, animals hunt, fungi decompose, protists are generic microbial slime subservient to all the former". Probably forget to staple cover sheets to their TPS reports as well.In the predatory foram case, you may be shrugging your shoulders and remarking that those forams are pretty damn huge anyway, so it's not that incredible. Alright, I'll grant you that. But what about a fairly small single-celled amoeba tackling nematodes in the soil?Life cycle of Theratromyxa, involving predation on food a little too large for its size followed by long-term digestion and slumber in cysts. Not a bad lifestyle. (Sayre 1973 J Nematol; Sayre & Wergin 1989 Can J Microbiol)Imagine you're living your life as a diminutive nematode, and suddenly a small creepy-looking branchy amoeba crawls toward you. Shivers descend down your non-existent spine as the amoeba extends its slender pseudopodia all over your body and gradually engulfs it. Your writhe in terror, but to no avail, for the creepy monster who just moments before appeared tiny and insignificant now has you inside a digestive vacuole full of acid and unfriendly enzymes. If you were lucky, some of your companions were engulfed along with you, so while packed in like sardines, you still have company. You wonder whether this is payback for all the evil you had wrought upon those poor plant roots. Little do you know your entire plight has been carefully planned by your self-proclaimed overlords from another phylum, just to get pretty pictures in the end:Light micrographs (left; Sayre 1973 J Nematol) and SEM of Theratromyxa (right; Sayre & Wergin 1989 Can J Microbiol). Image 6 shows quite nicely how Theratromyxa captures the nematode. This looks rather similar in principle to the feeding veil of dinoflagellate Protoperidium. Sometimes the amoeba can capture several nematodes at once. SEM shows amoeba enveloping a nematode.Theratromyxa has been considered for use as a biological control agent for the root-knot nematode (a very tiny group of nematodes, G. Meloidogyne. However, it wasn't particularly effective as excystment was rather slow, and there was no known method of speeding it up. Apparently, anastamosis (joining of numerous pseudopodia/amoebae) has been reported in previous studies, but Sayre 1973 did not observe any. But there still is the possibility of several Theratromyxa individuals (or their relatives) also ganging up on larger prey, as some other protists are known to do (eg. centrohelids cooperating in hunting larger ciliates).Theratromyxa is a Vampyrellid, a group of rather frightening amoebae, likely in the Endomyxa clade of Cercozoans/Rhizarians (see Pawlowski & Burki 2009 JEM; Parfrey et al. 2010 Syst Biol) (AFAIK, endomyxans are cercozoans, but considering the amount of stuff that's gradually settling in Endomyxa, perhaps the definition of cercozoa is bound to change eventually. I like 'Cercozoa' better than 'Filosea', the other subgroup of cercozoans; ie, it'd be nice to ditch 'Filosea', replace it with 'Cercozoa' and make Endomyxa not Cercozoans. Confused? Don't worry – just taxonomic musings.) Some other Vampyrellids are notorious for poking holes in fungi (Anderson & Patrick 1980 Soil Biol Biochem) and algae (life cycle), and then devouring the cells within. Not a very happy thought if you're a filamentous alga.By the way, some cercozoan amoeboflagellates can gang up on larger nematodes too, but I'll save that for another day.ReferencesSayre RM (1973). Theratromyxa weberi, An Amoeba Predatory on Plant-Parasitic Nematodes. Journal of nematology, 5 (4), 258-64 PMID: 19319347... Read more »
Sayre RM. (1973) Theratromyxa weberi, An Amoeba Predatory on Plant-Parasitic Nematodes. Journal of nematology, 5(4), 258-64. PMID: 19319347
Sayre, R., & Wergin, W. (1989) Morphology and fine structure of the trophozoites of Theratromyxa weberi (Protozoa: Vampyrellidae) predacious on soil nematodes. Canadian Journal of Microbiology, 35(5), 589-602. DOI: 10.1139/m89-094
- July 23, 2010
- 07:02 AM
- 66 views
Sunday Protist - Farming forams: a case of protistan agriculture
by Psi Wavefunction in Skeptic Wonder
"WTF, it's Friday already!" Friday? What Friday? You saw nothing.My previous two Sunday Protist attempts got derailed. With the first one, noticed there was quite a bit to say about them, and decided to postpone it for later as it was a big topic (and unrelated to my current work). Then I picked something relevant to my day job, y'know, two birds one stone, etc. And somehow that led me to paleontology. A warzone in paleontology. Complete and total clusterfuck. With potential inaccuracies here and there that I now need to sort out. Whilst we wait, I'll just do something quick: a case of a foraminiferan apparently growing bacteria and then eating them in perhaps one of the most non-human farming enterprises ever! (leafcutter ants are pretty much human at that phylogenetic distance...)Textularia blocki lives on seagrass. Many forams have interesting associations with seaweeds, ranging from internal parasitism to epiphytic attachment, usually via secretions of sulfated mucopolysaccharides, a fairly common material in the extracellular matrix. T.blocki, however, is a freely motile foram. It leaves peculiar 'grazing traces' as it crawls along the seagrass, without damaging the tissue beneath it:Left: T.blocki with grazing traces on blade of seagrass. Right: (Langer & Gehring 1993 J Foram Res)As made evident in the diagram, the traces consist of two parallel 'walls', consisting of pale whitish adhesive material, presumably containing mucopolysaccharides, devoid of sand grains or other contaminants. Curiously, some forams carried sand grains along, without depositing them. These secretions are formed by pseudopodia, or the 'business' part of the foram: an intricate network of reticulated feet with amazing cytoskeletal properties. When these secretions are left alone in seawater for 48h, a lush garden of bacteria sprung up specifically along the secretion traces:Bacterial gardens along the foraminiferan secretion traces. Note the relatively clean surface of the leaf outside the secretions, supporting that it is the adhesive mucous that attracts bacterial accumulation (Langer & Gehring 1993 J Foram Res)When released back into the medium containing the seagrass lined with traces, the forams approach the nearest trace and follow along it, suggesting they use some form of chemical sensing to determine where the secretions are and how they are oriented. The speed is then reduced, suggesting the foram is then busy grazing on their bacterial harvest.Thus, a 'mere' single celled organism can produce organised tracks of nutritious material, wait for their bacterial crop to grow, and subsequently harvest it. We like to think we invented agriculture. The more biologically-oriented among us point out leafcutter ant fungus gardens and aphid farming. Yet, agriculture has also evolved on the unicellular scale in a small humble foraminiferan living among blades of seagrass. Humbling, isn't it?Interestingly, a similar behaviour has been described gastropods like slugs and limpets, as their mucous also attracts bacterial growth. Convergence: when a good thing is chanced upon multiple times, it will likely be kept by several lineages independently. This applies to language and cultural evolution as well as that of biological organisms.We tend to have a deep conviction that cells are dumb blobs of goo, incapable of any sort of behaviour besides basic phototaxis or whatever. We think cells are just simple chemical response machines – which is true. But ultimately, so are we. There is no fundamental distinction between human social dynamics and the adventures of a crawling amoeba. The difference is all in the quantity and complexity of interactions – the higher the complexity, the more random (stochastic) the system appears (and to an extent, is). While I must concede that in terms of the number of components and pathways involved, human or ant behaviours are more complex than that of an amoeba, that does not mean the proverbial amoeba 'lacks' behaviour entirely.I've mentioned the cellular behaviour stuff before, probably too often for regular readers. Apparently, that idea needs restating though. Also, as a cell biologist, I find it quite...well, pleasing. It's nice that, ultimately, my subjects are no more or less machine-like than humans or plants. Furthermore, where I was heading with this originally, I think part of our notion of cells being 'stupid' comes from the obsession with our own cells. Animal cells are, in fact, quite simple and developmentally retarded. The cause is cell specialisation driven by multicellularity. Eg. an epithelial cell can now afford to lose the ability to hunt around for prey, it no longer needs to coordinate movement in any sophisticated manner, the life cycle can be simplified to terminal differentiation.Curiously, a similar problem plagues modern science and engineering: overspecialisation means that one must no longer have the same level of foundational education to survive, and thus we end up arguably knowing more about less, or perhaps knowing the same about less. I can suck at math or chemistry and get away with it. In the old days, people had to actually have a broader base just to function. Conversely, there was also less information floating around. Which is more efficient? Just as multicellularity vs. unicellularity, each system has its merits and drawbacks. So it's hard to tell.A while back I found a paper on cellular complexity in multicellular vs. unicellular organisms that needs to be discussed in greater detail eventually...---Random Link---ChrisM over at the wonderful Echinoblog (about the cooler deuterostomes; ok, hemichordates and ascidians are cool too) wrote about sperm-eating ciliates infesting starfish.Lots of things like sperm. For example, Monocystis is a gregarine with a penchant for earthworm sperm – infection rates are so high that if you slice up a worm from your backyard and smear the contents of its seminal vesicles on a slide, the chances are pretty good that you'll find some. And by 'some', I mean, LOTS. So if you're ever in the mood for some apicomplexans, all you need is an earthworm, a blade and a scope. There are parasites in pretty much anything and everything, so if you go around examining various animals, you may well find loads of cool protistan denizens in them. Many of which could be undescribed and, perhaps, new to science.Reference... Read more »
Langer, M., & Gehring, C. (1993) Bacteria farming; a possible feeding strategy of some smaller motile Foraminifera. The Journal of Foraminiferal Research, 23(1), 40-46. DOI: 10.2113/gsjfr.23.1.40
- July 14, 2010
- 07:42 AM
- 89 views
Carnivorous trees of the sea: Notodendrodes not as harmless as it looks
by Psi Wavefunction in Skeptic Wonder
Remember Notodendrodes and the spicule tree? Don't they look so much like harmless trees sitting around sunbathing like their plant counterparts? Not all tree forams are harmless. The microscopic marine world is full of surprises, like trees waving around their long sticky network 'feet' to trap and devour any traveler that happens by. Here's some wonderful shots of Notodendrodes caught in the act:The top left image shows a clump of Artemia caught by Notodendrodes, a big carnivorous tree foram. Note how the reticulopodia (pseudopodial networks) stretch between the branches like spiderwebs. Top right: SEM of the reticulopodial mesh of another species of Notodendrodes. Bottom: The tree foram in its natural setting, with a copepod attached (arrow). (Suhr et al. 2008 Mar Ecol Prog Ser)There some nice foram videos on this YouTube page, including shots of reticulopodia and a fairly large foram moving about in situ. This movie by a Japanese researcher includes clips of Artemia being captured starting at 0:50.Many forams are voracious predators, devouring anything from fellow protists to crustaceans and echinoderm and mollusc larvae. The following is Astrammina rara's rather impressive menu; all but two species were happily consumed:However, not all forams are carnivorous. Some are mediocre at best at capturing prey, and some, like Crithionina, are quite bad. This suggests a range of feeding habits from detritovory to carnovory to omnivory. Note how Gromia (not a foram, despite looking vaguely similar; placement somewhat uncertain, though most likely either close to forams or a cercozoan) fails to capture any prey. Also, dead specimens failed to catch prey, indicating the capture is intentional and requires a fully functioning cell, and not an accidental adhesion to something sticky. In fact, there is evidence for specific targetting of certain prey, which wouldn't be much of a stretch as many forams are quite picky in choosing their test material.I think this has some interesting – perhaps borderline philosophical – implications. Towards the end of the ciliate kleptoplasty post I mentioned how the traditional ecological terms often fail to describe the majority of life, which happens to be microscopic and play by some different rules. There's a greater problem in the approach of traditional ecology towards microbial life, however, and it even surfaced in a random chat with some ecology grad students. Namely, the treatment of all things microbial as the "bottom of the food web", ie. prey species created by evolution to feed cute fluffy animals. They have a similar attitude to plants as well: 'producers'. Fungi are 'decomposers'.Probably to people tracking bird migration out in the field, such crude terms do just fine, and we all must make crude approximations somewhere (or drown in details). However, as in any simplification, there's always a danger of skimming over interesting outliers. I disagree with the blanket treatment of protists (and bacteria, and anything else) as the "bottom of the food web" for two reasons:1. There are plenty of intricate interactions resulting in elaborate food webs (and, more generally, 'interaction webs'); a plethora of fascinating relationships is lost when one blurs them all into the 'prey for animals' category.2. Feeding by animals forms but a very tiny part of the overall diversity of microbe-animal interactions. An ecological framework must account for symbionts (mutualists, parasites and commensals) along with predation. Toxoplasma, arguably the most successful parasite of vertebrates ever, is a wonderful example of 'lower trophic levels' leeching 'up' the food web and running the show. You can't really draw an arrow from a cat or human to the modest apicomplexan, as it doesn't really consume its slaves. But you can't really not draw that arrow. It's complicated.(In fact, if organisms besides humans had Facebook, most of their relationship statuses would be set to "It's complicated". Groan all you want... =P)Lastly, our forams mentioned above also have ecological consequences on the megafauna in their environments. Astrammina rara is benthic, meaning it lives on the ocean floor (or, technically, any substrate). Suhr et al (2008) mention past studies indicating lower-than-usual densities of marine fauna in particular areas; these areas seem to match up with Astrammina's distribution. Presumably, the effects of predation on small fauna and larvae can be seen on the larger scale.Furthermore, the carnivorous forams seem to affect the survival strategies of the fauna around them (in hindsight, unsurprisingly): some echinoids have brood protection and settling strategies that may well have evolved in response to the lowly single celled protists they rightly fear. The authors suggest that the failure of Astrammina to capture larvae of the echinoid Acodontaster may be a result of the latter evolving a specific chemical defense against it.The 'scum' from the bottom of the foodweb can come up to bite some 'higher' organisms in the ass – whodathunk?ReferenceSuhr, S., Alexander, S., Gooday, A., Pond, D., & Bowser, S. (2008). Trophic modes of large Antarctic Foraminifera: roles of carnivory, omnivory, and detritivory Marine Ecology Progress Series, 371, 155-164 DOI: 10.3354/meps07693... Read more »
Suhr, S., Alexander, S., Gooday, A., Pond, D., & Bowser, S. (2008) Trophic modes of large Antarctic Foraminifera: roles of carnivory, omnivory, and detritivory. Marine Ecology Progress Series, 155-164. DOI: 10.3354/meps07693
- July 13, 2010
- 08:41 AM
- 95 views
Sunday Protist - Giant tree of spicules: Spiculidendron
by Psi Wavefunction in Skeptic Wonder
Christopher Taylor over at Catalogue of Organisms has a nice post on agglutinated Saccamminid foraminifera, and very recently wrote on the taxonomy and morphology of Pelosina, Pilulina and Technitella, wherein he brought up a fascinating paper on one hell of a bizarre foram: the 'spicule tree', initally mistaken for a gorgonian (sea fan). I'm going to leech off his find as he didn't specifically mention this tree foram in his post. Also, he mentioned Komokians before I did. Meanie. In all seriousness, go read his posts. For the phylogenetically inclined protistologists, the Komokian post is good food for thought.I'm going to slack off a bit this time. For an overview of the huge clade of awesome that is Foraminifera, see my earlier post here; for another tree foram, see Notodendrodes here.Foraminiferans are amazing creatures: some of them can be best described as giant cannibalistic carnivorous wads of sticky reticulated pseudopodia, capable of snaring and devouring small metazoans and Volvox colonies. They have the fastest microtubule growth rates in the eukaryotic kingdom - a whole two orders of magnitude greater than those of animals at a stunning 12µm/s! (animal cells grow microtubules at around 1-15µm/min.) (Bowser & Travis 2002 J Foram Res) Their pseudopodia are themselves capable of shearing flesh in a process so unique it deserved its own name: 'skyllocytosis' (Bowser 1985 J Protozool). Do not screw around with forams. They are scary.Most of them also have shells, but that's a story for some other day. Well, many stories, for many days. Forams are a huge and diverse group.The following specimen belongs to Astrorhizidae, a group of agglutinating forams - meaning their tests are composed of material from the environment, often very selectively picked. As implied by its name, the spicule tree, or Spiculidendron, composes its test entirely out of sponge spicules. Furthermore, this contraption reaches a stunning 60mm (6cm) in height, as a single-celled organism!Plant, animal or protist? A foram tree to shame all foram trees. A giant spicule-covered monster from the Caribbean tropics. (Rützler & Richardson 1996 Biologie)The paper mentions difficulties in determining whether the spicule tree bears a single nucleus or is coenocytic. Presumably, if it was that hard to find (though they had few specimens to work with), it may well be uninucleate like Notodendrodes. This would be quite cool as 6cm is one hell of a giant cell to be supported by a single nucleus. The cytoplasm also contains symbiotic dinoflagellates, making this tree foram even more like an actual tree.Note that this strange monster of a foram was only described in 1996. The age of exploration is far from over.ReferencesRützler, K., & Richardson, S. (1996). The Caribbean spicule tree: a sponge-imitating foraminifer (Astrorhizidae) Bulletin de l'Institut Royal des Sciences Naturelles de Belgique 66 (Suppl.), 143-151Bowser, S. (2002). RETICULOPODIA: STRUCTURAL AND BEHAVIORAL BASIS FOR THE SUPRAGENERIC PLACEMENT OF GRANULORETICULOSAN PROTISTS The Journal of Foraminiferal Research, 32 (4), 440-447 DOI: 10.2113/0320440BOWSER, S. (1985). Invasive Activity of Allogromia Pseudopodial Networks: Skyllocytosis of a Gelatin/Agar Gel The Journal of Eukaryotic Microbiology, 32 (1), 9-12 DOI: 10.1111/j.1550-7408.1985.tb03005.x... Read more »
Rützler, K., & Richardson, S. (1996) The Caribbean spicule tree: a sponge-imitating foraminifer (Astrorhizidae). Bulletin de l'Institut Royal des Sciences Naturelles de Belgique 66 (Suppl.), 143-151. info:/
Bowser, S. (2002) RETICULOPODIA: STRUCTURAL AND BEHAVIORAL BASIS FOR THE SUPRAGENERIC PLACEMENT OF GRANULORETICULOSAN PROTISTS. The Journal of Foraminiferal Research, 32(4), 440-447. DOI: 10.2113/0320440
BOWSER, S. (1985) Invasive Activity of Allogromia Pseudopodial Networks: Skyllocytosis of a Gelatin/Agar Gel. The Journal of Eukaryotic Microbiology, 32(1), 9-12. DOI: 10.1111/j.1550-7408.1985.tb03005.x
- June 26, 2010
- 10:28 AM
- 136 views
Criminally photosynthetic: Myrionecta, Dinophysis and stolen plastids
by Psi Wavefunction in Skeptic Wonder
The microbial world is full of vicious beasts. Yes, much of microbial life is cute and cuddly in one way or another. But that doesn't stop many of them from making wolverines seem docile by comparison. There is an entire mafia out there built around...organ theft; including some multicellular players as well, in case you thought animals were saintly. Today we'll look at some famous thieving masterminds of the plastid black market, but keep in mind that there are many more fascinating relationships involving keeping entire organisms or their parts alive within the host, and vastly more oddities that have still escaped human attention (not hard to do, actually).Let's start off the messy subject with a pretty diagram summarising the major plastid hoarding events of the [moderately] distant past:Pac-Man!* Today all we need to do is appreciate the overall big picture: there were numerous symbiotic events and by about tertiary endosymbiosis, it gets messy. Not pictured are the cases of more-or-less transient kleptoplasty (plastid-theft), which would do serious harm to the readability and aesthetic qualities of this diagram. (Keeling 2004 Am J Bot; free access) For those keen on extra gory details of plastid endosymbiosis, see this recent review.*If somebody were to make a game of Pac-Man: Endosymbiosis Edition...Today's plastidial saga will involve an arduous journey from the cyanobacterium to the red algal endosymbiont of the cryptomonad, to the subsequent ingestion by a ciliate and a dinoflagellate. In fact, just keep in mind that the cryptomonad itself is the result of a hungry heterotroph getting a habit of devouring red algae and developing a case of terminal indigestion, ultimately gaining a plastid and plastid-targetting genes in its own nucleus. The cryptomonad in particular happens to be really awesome in another way: it actually still retains the original, eukaryotic, red algal nucleus of its former prey! That nucleus has been badly shrunk in the wash, and the genome is essentially on crack, but that's a long story for some other day.Just so you get an idea of what a cryptomonad roughly looks like:Cryptomonas. Note its very diminutive size. Source: Micro*scope. We're about to move on to the sleazy thieving ciliates and dinoflagellates. But first, we must establish how kleptoplasty (lit. plastid theft) differs from endosymbiosis. To clarify, I use 'symbiosis' as a general term for an intimate interaction between two different species, including parasitism, mutualism and commensalism. Thus, an endosymbiont needn't feel the same way about the relationship as its host, and very often doesn't. Keep in mind that it is often not very obvious which exact category the symbiosis falls into, as nature doesn't particularly care for our naming fetish.Endosymbiosis, in the context of organelles and other intracellular stuff, typically entails the complete engulfment of another organism by the cell. Once gene transfer occurs between the genomes of the two organisms, some declare the endosymbiont is now officially an organelle. The endosymbiont-organelle debate is old, stale and utterly pointless; thus, as I have declared in a previous post, I like to call plastids and mitochondria 'endosymbionts' and the more questionable cases, like Perkinsela, 'organelles'. That way, I can piss off just about everyone. Ha!Then there is the much-awaited plastid theft, where only the plastid itself of the failed endosymbiont is retained, with the rest of it typically digested away. The katablepharid Hatena which Labrat wrote a wonderful post about, is a striking case of kleptoplasty (and only discovered this past decade!). The intensity of kleptoplasty, as well as endosymbiosis, vary greatly from transient plastids (or endosymbionts) that are not essential to the host, to mostly permanent plastids or endosymbionts that are retained indefinitely, capable of reproducing on their own, and completely obligatory for the host's survival. This is nicely summarised in this diagram from a recent review on acquired photosynthesis by Stoeker et al 2009:Two ways to get a plastid: 1) steal a plastid-bearing alga and lock it in your basement keep it alive within you (endosymbiosis); 2) mug the alga, steal its plastid and try to keep it alive yourself. Along the two paths lie multitudes of intermediate steps different in the persistence of the plastid (how long it lasts) and how dependent the host is upon it. (Stoecker et al. 2009 Aquat Microbiol Ecol)In the endosymbiotic pathway, nucleomorphs (and the original plastidial prokaryotic genome) suggest the permanent associations we know among the 'normal' algae come from the endosymbiotic path, as there is evidence for whole host retention at some point. However, the data do not entirely rule out some independent secondary plastid acquisition via kleptoplasty rather than endosymbiosis. As for tertiary plastidial symbionts, it gets fun. The classic persistent cases like Kryptoperidinium tend to have a whole endosymbiont, nucleus and all, so the endosymbiotic pathway is also more likely, cut things like Dinophysis, on the other hand, are just weird.Now, at last, our long-awaited thief: the ciliate Myrionecta rubra (=Mesodinium rubrum):Myrionecta rubra (originally Mesodinium rubrum); c - cirri; ChC - chloroplast complexes; ECB - equatorial ciliary band (Taylor et al. 1969 Nature) Right: SEM of ... Read more »
Garcia-Cuetos, L., Moestrup, �., Hansen, P., & Daugbjerg, N. (2010) The toxic dinoflagellate Dinophysis acuminata harbors permanent chloroplasts of cryptomonad origin, not kleptochloroplasts. Harmful Algae, 9(1), 25-38. DOI: 10.1016/j.hal.2009.07.002
Johnson, M. (2010) The acquisition of phototrophy: adaptive strategies of hosting endosymbionts and organelles. Photosynthesis Research. DOI: 10.1007/s11120-010-9546-8
Johnson, M., Oldach, D., Delwiche, C., & Stoecker, D. (2007) Retention of transcriptionally active cryptophyte nuclei by the ciliate Myrionecta rubra. Nature, 445(7126), 426-428. DOI: 10.1038/nature05496
Keeling, P. (2004) Diversity and evolutionary history of plastids and their hosts. American Journal of Botany, 91(10), 1481-1493. DOI: 10.3732/ajb.91.10.1481
OAKLEY, B., & TAYLOR, F. (1978) Evidence for a new type of endosymbiotic organization in a population of the ciliate Mesodinium rubrum from British Columbia. Biosystems, 10(4), 361-369. DOI: 10.1016/0303-2647(78)90019-9
Park, M., Kim, S., Kim, H., Myung, G., Kang, Y., & Yih, W. (2006) First successful culture of the marine dinoflagellate Dinophysis acuminata. Aquatic Microbial Ecology, 101-106. DOI: 10.3354/ame045101
Stoecker, D., Johnson, M., deVargas, C., & Not, F. (2009) Acquired phototrophy in aquatic protists. Aquatic Microbial Ecology, 279-310. DOI: 10.3354/ame01340
TAYLOR, F., BLACKBOURN, D., & BLACKBOURN, J. (1969) Ultrastructure of the Chloroplasts and Associated Structures within the Marine Ciliate Mesodinium rubrum (Lohmann). Nature, 224(5221), 819-821. DOI: 10.1038/224819a0
Wisecaver, J., & Hackett, J. (2010) Transcriptome analysis reveals nuclear-encoded proteins for the maintenance of temporary plastids in the dinoflagellate Dinophysis acuminata. BMC Genomics, 11(1), 366. DOI: 10.1186/1471-2164-11-366
- June 21, 2010
- 09:02 AM
- 126 views
Sunday Protist - Lagynion: bottled algae
by Psi Wavefunction in Skeptic Wonder
Quick one today as I should really be writing a chapter, as well as the post on plastid thiefs some of you wanted. And haptophytes. Have I mentioned my ADD tendencies?While I find ochrophytes (large group including diatoms and kelps) a bit too phycological for my tastes, some of them are actually really cool, especially Chrysophytes - the 'golden algae'. Chrysos include things like scaly flagellates (Paraphysomonas) and Dinobryon which makes colonies that look like trees of stacked wine glasses. A while ago we had bottled ciliates, and this time the Chrysophytes offer us a few bottled algae, especially the flask-shaped Lagynion.A happy(?) clump of photosynthetic flasks, of Lagynion. Source: Micro*scope.The lorica consists of organic material. The progeny following division are released as little zoospores bearing the ridiculously complicated flagella characteristic of ochrophytes (one of them too short to be easily visible). Then the zoospores settle down, become amoeboid and grow themselves a new flask. As far as I could gather, that's pretty much all there is to say about Lagynion at the moment. But it still looks pretty cool!1. Side view. Arrowheads indicated a rib structure surrounding the 'flask'. 2 and 3: top views of three Lagynion cells showing optical sections through the base and the neck regions, respectively. 4. TEM of 'flask'. Note the plastids (C) and the nucleus (N). V - peripheral vesicles. In short, plastids in a bottle. (O'Kelly & Wujek 2001 Eur J Protistol)In fact, there's a whole family of bottled, and often amoeboid, algae called Stylococcaceae (eg. see Nicholls 1987 J Phycol), but they are so obscure it's painful to find much literature on them, or even decent pictures. Especially since by the time they get digitised, a lot of the old images become completely illegible. But here's another member of the family bearing slightly different glassware, Chrysopyxis:Source: Micro*scopeNow to do real work and then write up some of the really exciting stuff I came across lately. And crush my writer's block with something sharp and heavy. Really annoying when you can't write anything because, well, you can't write anything. Wish brains came with instruction manuals...ReferencesNicholls, K. (1987). CHRYSOAMPHIPYXIS GEN. NOVA A NEW GENUS IN THE STYLOCOCCACEAE (CHRYSOPHYCEAE) Journal of Phycology, 23 (3), 499-501 DOI: 10.1111/j.1529-8817.1987.tb02537.xO'Kelly, C., & Wujek, D. (2001). Cell structure and asexual reproduction in Lagynion delicatulum (Stylococcaceae, Chrysophyceae) European Journal of Phycology, 36 (1), 51-59 DOI: 10.1080/09670260110001735198PS: Hardly relevant but kind of newsworthy: First Phaeophyte genome sequenced! (Cock et al. 2010 Nature) Until now, the only complete Stramenopile(=Heterokont) genomes were a couple diatoms and oomycetes. Ok, there's still many more to go but Phaeophytes can be interesting in terms of studying the evolution of multicellularity. Also, the ochrophyte clade is a phylogenetic mess; not that single whole genome data means much but could perhaps helps calm the harsh seas somewhat.... Read more »
Nicholls, K. (1987) CHRYSOAMPHIPYXIS GEN. NOVA A NEW GENUS IN THE STYLOCOCCACEAE (CHRYSOPHYCEAE). Journal of Phycology, 23(3), 499-501. DOI: 10.1111/j.1529-8817.1987.tb02537.x
O'Kelly, C., & Wujek, D. (2001) Cell structure and asexual reproduction in Lagynion delicatulum (Stylococcaceae, Chrysophyceae). European Journal of Phycology, 36(1), 51-59. DOI: 10.1080/09670260110001735198
- June 9, 2010
- 05:07 AM
- 205 views
Clearing up eukaryotic life histories
by Psi Wavefunction in Skeptic Wonder
I can still vaguely recall the horrid hell that was my second year "non-vascular 'plant'" course (valid contender for most polyphyletic course in existence...) - amid the poorly explained phylogenetic clusterfuck, we also had to cram life cycle diagrams from hell. Ever thought red algae looked cute? Not quite so much after realising you get three fundamental life cycle phases to plow through...the night before a final, as it always is. In hindsight, it actually makes a lot of sense, once you grasp some basic principles. Somehow, I missed those the first time around, and then wondered what the hell went wrong. Warning: This is a bit of a rant. For the meat, skip to the figure. The damnationOne of those key concepts is the haploid-diploid variation found in many, if not most (if not, secretly, all) eukaryotes. You know the whole thing with syngamy and meiosis and gametic vs. zygotic vs. sporic life histories. You may even wish I hadn't reminded you. Click here if you'd like to experience the wonderful feeling of intense confusion again. So basically, eukaryotes can be haploid or diploid. Typically they have ways of switching between the two phases: diploid -- haploid = meiosis (typically), haploid -- diploid = syngamy (again, roughly). To make things more fun, there may also be several distinct diploid and haploid stages, but let's ignore those for now. Now, it logically follows that there may be variation in how 'prevalent' a certain stage is for various organisms. Let's call it the 'dominant' stage, just for kicks. Now, how do you define 'dominant'? Well, for humans, it's obviously the part of your life you're an 'individual'. Ok this gets weird when said 'individuals' can clone themselves; also, a bit too philosophical. Let's reword that: It's obviously the stage in your life you're multicellular and big and stuff. Baker's yeast, for example... hang on, what's the big multicellular stage in yeast? Errr... scratch that. Ok, the stage an organism spends most of its time in. Great, works so far. Yeast is most usually haploid. What about moss? It's roughly equal (for the sake of the argument) in both haploid and diploid stages. So it's sporic. I admit to being a little slow at times, but that seriously confused the fuck out of me -- it seemed arbitrary! How exactly do you decide whether an organism has one or multiple "dominant" stages?We've been told to "look where meiosis happens". Now this is where it becomes absolute and total mindfuck, on steroids and LSD. Remember the 'gametic', 'zygotic' and 'sporic' life histories? You know what else they're officially(!) called? Gametic, zygotic and sporic...MEIOSES. That's right. We have gametic meiosis, zygotic meiosis and sporic meiosis. Now, sit back and savour the absolute chaos that this naturally incites in young minds yet to be protected by the hard-ass defensive shell your brain produces from years of bitter academic cynicism. Done? Borderline mental abuse, ain't it?Of course, while none of those terms have a single redeeming quality besides being physically pronounceable, the worst, by far, is 'gametic meiosis'. Last time I checked, there are no documented case of haploid cells consistently/normally undergoing meiosis. (allowing it has somehow been induced artificially in haploids - who knows) So that's absurd. Even speaking from a field where biological "laws" need not apply. I'm happy to know that someone with qualifications agrees with this, and also has a nice rant on the topic. Of course, I'd say we should do away with 'gametic', 'zygotic' and 'sporic' altogether, but more on that later. We've also been told "the big, obvious stage [presumably, multicellular] is dominant" Again, last time I checked, Chlamydomonas doesn't exactly jump out of the culture medium and grow before you into a giant... SuperChlamy... or something. That would be really cool for a cartoon character, but most life doesn't exactly strive to be visible to the human eye or anything. In fact, it's much better to not be...A slightly more sensible point was "look where feeding happens". Great, so sperm are now a dominant stage? If I recall, they do absorb nutrients. Are we gonna go as far as define what manner the nutrients must be obtained in? The lesser known life of Dictyostelium involves cuddling up with a mate, fusing, forming a cyst and then baiting unsuspecting haploid dictys with cAMP...to devour them! How about "the stage that can live freely"? Well, then many parasites now have no life, and are very sad. Or "the stage that lasts the longest". Well, many things can fuck, encyst, and hang out for what is an eternity compared to their mitotic cycles. Some organisms can spend more time in resting stages than in active ones - ever wondered how a puddle can come back to life as quickly as it dries up?In the end, I figured this was more of a fuzzy philosophical question, with ultimately everything being somewhat sporic-Salvation at last!-until randomly wandering across this neat little diagram today: A sensible summary of a) Haplontic, b) Diplontic and c)Haplodiplontic life histories. ( Houdan et al 2004 Syst Biodiv based on (and greatly improved from, IMO) Valero et al. 1992 TrEE)Do you see the difference? At last, a clear, crisp definition! The dominant stage is the one where mitosis occurs, duh! Perhaps it'd help to add 'reproductive' meiosis, to take care of those pesky little exceptions (some multicellular lineages). And personally, I prefer 'haplontic' vs. 'zygotic'. Zygotic sounds very diploid to me. That term owes me a nice chunk of my grade for that 'non-vascular plant' course. 'Haplodiplontic' is wonderful too as you don't have to sit there wondering what a 'spore' is. It's straightforward, concise and universally applicable. Humans? Diplontic - sperm and eggs don't reproduce mitotically. Dictyostelium? Haplontic - diploid stage quickly followed by meiosis without any mitotic divisions. Moss? Haplodiplontic - both haploid and diploid forms divide mitotically, in this case to form large multicellular organisms. Our favourite beer-making Saccharomyces? Haplodiplontic, actually - it can happily ... Read more »
Houdan, A., Billard, C., Marie, D., Not, F., Sez, A., Young, J., & Probert, I. (2003) Holococcolithophore-heterococcolithophore (Haptophyta) life cycles: flow cytometric analysis of relative ploidy levels. Systematics and Biodiversity, 1(4), 453-465. DOI: 10.1017/S1477200003001270
Valero, M. (1992) Evolution of alternation of haploid and diploid phases in life cycles. Trends in Ecology , 7(1), 25-29. DOI: 10.1016/0169-5347(92)90195-H
- May 25, 2010
- 08:09 AM
- 148 views
Sunday Protist -- Blue Mats of the deep sea: Folliculinopsis
by Psi Wavefunction in Skeptic Wonder
Far, far away, in the land of eternal darkness along the base of the deep sea hydrothermal vents of the Juan de Fuca Ridge lie stretches of surface covered by 'blue mats'.(Kouris et al. 2007 Mar Ecol)These blue mats are produced by yet another tube-forming denizen of the hydrothermal vents. To non-tube-dwellers like us they may even look vaguely reminiscent of the much more famous giant tube worms, and the concept is quite similar up until that point.However, if you look inside a tube with its live host, something distinctly non-annelid peers out:This creature is, in fact, a ciliate - a relative of the elegant Folliculina (referred to in the good ol' days as the "bottle-animalcule"), Folliculinopsis sp., a heterotrich like the giant Stentor:Folliculinopsis. The two long 'wings' or 'ears' sticking out are its peristomal lobes, which can be seen in the preceding SEM. (Ji et al. 2004 J Ocean Univ China)Folliculinopsis is host to countless bacterial symbionts; in fact so lushly the bacteria thrive on it that one can barely see the ciliate beneath them! Presumably, these bacteria may be involved in chemical defense, protection from the rather toxic surrounding environment or assist in metabolism. Symbiosis with prokaryotes seems to be fairly common for eukaryotes living awkward (extreme) environments, in large part because prokaryotes are simply amazing at biochemistry unlike their metabolically-challenged nucleated counterparts.SEMs and TEM of symbiotic bacteria on Folliculinopsis sp. The lorica is covered mostly with filamentous bacteria (top left) whereas the surface of the ciliate is entirely covered with coccoid and rod-shaped episymbionts (bottom two SEMs). Moreover, the inside of the ciliate is full of bacteria-containing vacuoles, as seen in the TEM (near the cortex). (Kouris et al. 2007 Mar Ecol) In another folliculinid, Eufolliculina, the surface of the peristomal lobes has a peculiar feature: short membrane-covered pins at the base of each cilium. Mulisch (1991 Cell Tissue Res) proposes these pins may act as sensory organelles, perhaps to transmit oriented mechanical stimuli. The cilia have a swelling at the level of the pin, filled with peculiar granular particles with potential involvement in calcium regulation (as you may recall from intro-level physiology, Ca2+ is quite popular in signaling systems). Similar cilium-pin complexes have also been found in other folliculinids, suggesting it may be a shared feature.Cilia with sensory pegs at the base (arrows). (Mulisch 1991 Cell Tissue Res)The cilium-peg complex reminds me of sensory hairs or sensilla on insects. Mulisch relates it to the hydrozoan cnidocil in the cnidocyst, or the stereocilia (microvili) at the base of the kinocilium in vertebrate sensory hair bundles. Perhaps this is yet another instance of ultimate convergence, as there is ultimately a finite number of ways particular functions can be performed, and evolution's random walks are bound to chance upon some more than once.The biology of protist sensory mechansims and overall behaviour is still vast, mysterious, murky territory desperately in need of serious investigation. Unicellular organisms have complex behaviours just like multicellular ones, and are no more 'mere automatic responders to stimuli' than we are (due to our cumbersome complexity, much more random noise tends to creep in; perhaps where creativity comes from...); somehow, without a brain or even a nervous system, many unicellular organisms are nevertheless quite capable of performing complex behaviours in response to various stimuli.This topic was quite popular in the early 20th century, but seems to have been largely abandoned today (in unicellular organisms). Considering the volumes of papers published daily on cell motility in tissue cultures, would it be too much to ask for some investigation of more intelligent cell types, ie. those that also act as entire organisms? Surely a ciliate must be much m... Read more »
Ji, D., Lin, X., & Song, W. (2004) Complementary notes on a ‘well-known’ marine heterotrichous ciliate, Folliculinopsis producta (Wright, 1859) Frauré-Fremiet, 1936 (Protozoa, ciliophora). Journal of Ocean University of China, 3(1), 65-69. DOI: 10.1007/s11802-004-0011-1
Kouris, A., Kim Juniper, S., Frébourg, G., & Gaill, F. (2007) Protozoan?bacterial symbiosis in a deep-sea hydrothermal vent folliculinid ciliate (Folliculinopsis sp.) from the Juan de Fuca Ridge. Marine Ecology, 28(1), 63-71. DOI: 10.1111/j.1439-0485.2006.00118.x
Mulisch, M. (1991) Ultrastructure and membrane topography of special ciliary organelles in the ciliate Eufolliculina uhligi (Protozoa). Cell and Tissue Research, 265(1), 145-150. DOI: 10.1007/BF00318148
- May 12, 2010
- 05:07 AM
- 136 views
Sunday Protist -- Tachyblaston: A suctorian parasite of suctorians
by Psi Wavefunction in Skeptic Wonder
[it's totally still Sunday in someone's mind somewhere...right?]Reading old protistology books can be quite a frustrating exercise: image you come across a really cool-looking organism, try to follow up on what happened to it since, and discover it's only been written up once in the distant past and neglected ever since. This happens to a very annoying percentage of organisms described in those older books (newer books tend to forget the phantom and near-phantom species). Now this organism in particular at least has a very detailed source behind it, but alas! ...in German. I saw it in Grell's (1973) Protozoology, and the original description comes from... Grell 1950 . The former I have an English copy of, the latter I do not. So don't expect much detail.Ecologists often lump microorganisms together as 'decomposers' (at least in undergrad courses); those of us living in a different scale of things beg to differ. From an intro ecology text, you get the idea that ecology somehow ceases to happen once you reach a certain size or phylum, and everything's just a part of this amorphous blob that exists to recycle nutrients so that the rest of us can live on. Shockingly enough, this amorphous blob has a whole ecosystem of its own, complete with predators and photosynthesisers and those who do both, as well as parasites and mutualist endosymbionts and saprophytes, etc. They interact with each other in ways not in the slightest less interesting than fluffy animals. In the microscopic world, cells become bodies that, just like ours, can get hunted, infected or benefited by some other organism. Or host a pile of commensals (who do exist, by the way, by similar arguments that Nearly Neutral Theory employs for mutations)*Zoological ecologists also tend to treat plants as 'those things that exist for animals to eat', which annoys the hell out of anyone dealing with plants. On the first day of ecology the instructor causally mentioned that 'plants don't do much in the way of behaviour', and thus the course will largely ignore them. I expressed disagreement after class, noting there is little fundamentally different between a plant biochemical response leading to, say, discharge of toxins or some regulatory change, and an animal biochemical response leading to observable [to our eye] mechanical change. Yeah, this is why I have difficulty talking to the more 'traditional' biologists sometimes...but that is completely off-topic. Remember how crabs can sometimes be covered in sea anemonies? Many smaller crustaceans can often be covered in organisms superficially resembling miniature sea anemonies - namely, Suctorians - highly derived (=weird) ciliates covered in miniature tentacles. Suctorians also reproduce by budding, as opposed to conventional symmetrical mitosis employed by the canonical ciliate. Just like sea anemonies and other cnidarians, suctorians also have stalked and swarming forms, like the polyp vs. medusa destinction in the former. Which is quite unsurprising, really, as aquatic sessile organisms usually use specialised free-swimming forms to spread. But still another cool bit of ultimate convergence discussed a couple posts ago.Top: A copepod covered in suctorians; an SEM of Ephelota gemmipara from the copepod. (Fernandez-Leborans et al. 2005 J Nat Hist) Bottom: Ephelota superba, suctorian episymbiont of Antarctic krill. Quite reminiscent of an anthozoan. (Stankovic et al. 2002 Polar Biol)Now, imagine a microscopic sea anemone being parasitised by another. I'm not sure whether there are any cnidarian parasites of other cnidarians (wouldn't be too surprised), so the analogy stops around here. The awesome does not, however: parasites are never truly simple. Tachyblaston's infancy consists of finding an Ephelota, attaching itself and piercing the cell membrane to leech off the cytoplasm. Over time, the entire cell can become filled with parasites. During this stage, the parasite buds to produce swarmers.Tachyblaston invading Ephelota cell body. Right: Tachyblaston budding. (Grell 1950 Z.Protistenk)Afterwards, the swarmers swim around and attach themselves to an Ephelota stalk, where they themselves form a stalked cup structure. There the parasite buds multiple times, yielding a cup full of Tachyblaston, which is subsequently emptied as the buds (this time with a single thick tentacle, according to Martin 1909) evacuate and crawl up the stalk toward the main cell body of Ephelota to infect it and start the cycle over.... Read more »
Fernandez-Leborans, G., Freeman, M., Gabilondo, R., & Sommerville, C. (2005) Marine protozoan epibionts on the copepod Lepeophtheirus salmonis , parasite of the Atlantic salmon. Journal of Natural History, 39(8), 587-596. DOI: 10.1080/00222930400001525
GONG, J., GAO, S., ROBERTS, D., AL-RASHEID, K., & SONG, W. (2008) n. sp. (Ciliophora, Phyllopharyngea, Cyrtophoria): Morphological Description and Phylogenetic Analyses Based on SSU rRNA and Group I Intron Sequences . Journal of Eukaryotic Microbiology, 55(6), 492-500. DOI: 10.1111/j.1550-7408.2008.00350.x
Grell, K. (1950) Der Generationswechsel des parasitischen Suktors Tachyblaston ephelotensis Martin. Zeitschrift f�r Parasitenkunde, 14(5). DOI: 10.1007/BF00260027
Martin, CH. (1909) Some Observations on Acinetaria: Part I.—The " Tinctin-kbrper " of Acinetaria and the Conjugation of Acineta papillifera. Quarterly journal of microscopical science, 53(2), 351-389. info:/
- May 11, 2010
- 05:57 AM
- 82 views
Tree of Roots
by Psi Wavefunction in Skeptic Wonder
Flagellar roots, that is. Tree of phylogenetic roots would be another fun project though...You know when you see a page full of diagrams and get overcome by this urge to map them onto some phylogeny just for the hell of it? Especially when your other option is to actually write up the results and discussion sections your supervisor's sort of waiting for? (wrote two whole paragraphs' worth today, so I can take the rest of the day off, right?) Anyway, here comes Sleigh 1988 BioSystems p279, modern phylogeny edition:Phylogeny of Sleigh representations of flagellar root structures. Diagrams from Sleigh 1988 BioSystems; phylogeny based on A Tree of Eukaryotes v1.2 (complete references therein). Sleigh came up with a way to represent the structure of flagellar root apparatuses in order to compare them between various groups. These diagrams are used today by people working with protist cytoskeletons, and are reportedly a pain in the ass to make (rather unkind on one's 3D imagination capabilities). The flagellar root was traditionally considered to be a reliable character for taxonomic work, although it seems to be rather dangerous in some cases, as morphological any traits often tend to be. The flagellar root apparatus is quite complicated, and very often is responsible for the organisation of the rest of the cell. An annoying thing about them is how little is often known about the biochemistry of the various root elements, as materials besides tubulin can be freely used. In fact, older literature is full of descriptions of various fibrillar systems that have yet to be followed up on with modern cell biology techniques.Luckily, I somehow resisted the temptation to add other people's Sleigh diagrams onto the tree; hopefully won't succumb any time soon as I actually have real work to do. Hopefully fate won't take me to Simpson 2003 anytime soon...Does anyone else find making diagrams quite...relaxing?(Sunday Protist on its way...keep on getting distracted while looking stuff up for it)ReferenceSLEIGH, M. (1988). Flagellar root maps allow speculative comparisons of root patterns and of their ontogeny Biosystems, 21 (3-4), 277-282 DOI: 10.1016/0303-2647(88)90023-8... Read more »
SLEIGH, M. (1988) Flagellar root maps allow speculative comparisons of root patterns and of their ontogeny. Biosystems, 21(3-4), 277-282. DOI: 10.1016/0303-2647(88)90023-8
- May 5, 2010
- 05:02 AM
- 141 views
Convergent evolution between shrunken animals and bloated protists
by Psi Wavefunction in Skeptic Wonder
Our invertebrate zoology textbook, being a good couple decades behind schedule as any textbook ought to, felt rather heavily biased against molecular phylogenetic analysis, and rather conservative in sticking to traditional taxonomy in spite of contradicting molecular data. In fact, towards the end somewhere the authors rather explicitly pointed out that molecular phylogenies are not to be trusted, especially when in disagreement with embryological data.Here we run into the age-old problem in evolutionary biology: how do you reconstruct the past is the models of evolution you use are based on your...reconstructions of the past? Hah, as with any other interesting problem in life, you have to do both simultaneously, devoid of simple algorithms. Dismissing molecular phylogenies because they disagree with your pet theories on morphological evolution is just stupid. The non-photosynthetic stramenopiles(=heterokonts), for example, include things that were once, based on morphology, considered as: yeast, filamentous fungi, 'heliozoa' (group now completely defunct) and ciliates. Molecular phylogenies, while definitely full of their own flaws, eventually resolved that mess.Curiously, it seems there may be a bit of a problem with bacterial phylogenies being overrated in spite of the organisms and their biology. So while traditional taxonomy fails there as well, it's as if the field got a little carried away with sequences. Part of the reason may be that there seems to be very little communication between cell and evolutionary bacteriologists, emphasised by the stark absense of organism in evolutionary discussions and evolution in organismal ones. Which is another thing that makes protistology a pretty awesome field - there appears to be at least some semblance of balance and sanity between organismal and evolutionary protistologists, perhaps because there's so few of them to begin with.Anyway, back to our invert zool text, one major drawback of clumping things together by morphology is that smaller things tend to go together that way. Obviously, sharing size does not imply any phylogenetic closeness; nor does the level of structural complexity. Plagued by past notions of a progression towards increased complexity, many taxonomists lumped the 'simpler' incertae sedis taxa together.One such example was the acoelomate/pseudocoelomate/coelomate concept, where the inner body cavity (coelom) became progressively more complex as proto-bilaterians evolved into acoelomate flatworms, then pseudocoelomate nematode-like intermediates and finally acheived the true coelom of arthropods and vertebrates. From the morphological perspective, that makes sense. However, along came molecular data and cast this neat little story into the rubbish pile, revealing that many of the acoelomates and pseudocoelomates have secondarily reduced coeloms, derived from a true coelom. Thus, Acoelomata and Pseudocoelomata kind of exploded all over the tree. Much like 'yeasts' and 'heliozoans' and 'rhizopods' (amoebae, forams, etc).Structural complexity is very dangerous, as evolution wanders about rather aimlessly and has little against losing complexity if it can. In fact, selective pressures tend to favour simplicity, and to put it crudely, reduction of complexity tends to be adaptive more often than bloating. I've rambled on about this before, but this is to emphasise that this concept is actually kind of important and useful, and not just idle philosophising. It is actually dangerous to assume some sort of adaptive search for complexity as shown in cases like those of Acoelomata and Archaezoa.This leads us to the next taxonomic 'clump' - small metazoans, or 'meiofauna'. Meiofauna include Loriciferans, Rotifers, Gastrotrichs and the rather adorable Tardigrades. Many of them weren't clumped together seriously as much as simply due to lack of any information about them, considering they sadly don't fare well in the charismatic megafauna beauty contest. Turns out that meiofauna tend to be secondarily miniaturised. There is only so many ways an organism can be shrunk and still viable, thus convergence becomes a rampant feature in miniaturisation, the central theme of Rundell & Leander 2010 BioEssays:Latest sketch of the metazoan phylogeny with representative meiofauna depicted in the images, where applicable. Very nice of them to put metazoa into the broader eukaryotic perspective in the top left corner! As meiofauna are quite widespread over the metazoan phyla, it is emphasised that a better understanding of these groups is crucial to properly reconstruct metazoan evolution and diversity. Microorganisms being important...another issue in need of reminders every five years or so? (Rundell & Leander 2010 BioEssays)Rundell & Leander focus on interstitial organisms (those of the intertidal zone) and note the prevalence and importance of convergent evolution between various independently reduced animals, such as adult loriciferans and larval priapulids; and adult vs. larval ostracods and barnacles, respectively:a) adult loriciferan b) larval priapulid c) adult ostracod d) barnacle larva (Cypris stage) Scalebars: a - 30um; b-d - 100um. (Rundell & Leander 2010 BioEssays)Of course the comparisons at this stage are superficial, but still a good lesson in the prominence of convergent evolution and the dangers of morphological lumping. Furthermore, they proceed to point out convergent features shared with some protistan representatives from the same environment: ciliates. Meiofaunal taxonomy is plagued by cases of well-trained zoologists failing to distinguish ciliates from rotifers and cryptic small metazoa (there was one cryptic species mentioned in the textbook that was obviously a ciliate based on the description, especially the 'dispersal by transverse fragmentation' part... can't find it at the moment, perhaps someone might know what I'm talking about? Name starts with a C or an S...), and there may be good reasons for that:a) A gastrotrich b) A [hypotrich] ciliate. Note the dorsal spines and dense ventral cilia on both. Incidentally, both are benthic, so this is rather unsurprising, but still cool considering the former is a case of size reduction whereas the latter is a case of a size increase. c-d) stalked rotiferConochilus e) stalked ciliate Epistylis. They are both capable of rapid contractions in a very similar manner. Again, only so many ways one can be a stalked colonial organism of this size and eco... Read more »
Rundell, R., & Leander, B. (2010) Masters of miniaturization: Convergent evolution among interstitial eukaryotes. BioEssays, 32(5), 430-437. DOI: 10.1002/bies.200900116
- April 26, 2010
- 12:20 AM
- 141 views
Sunday Protist -- Rostronympha and latest parabasalian taxonomy
by Psi Wavefunction in Skeptic Wonder
Since I just spent hours staring at onychophorans (instead of studying), gonna skimp out on the Sunday Protist this week. So here's a wonderful alien-looking freak with a proboscis, Rostronympha; I totally demand an SEM of this, by the way:Parabasalid Rostronympha. Image by Guy Brugerolle via Micro*scope.I can't find the original description at the moment, but vaguely recall having searched for it ambitiously once and failed miserably. It's supposed to be (Duboscq, Grassé & Rose, 1937), with a later mention in PP Grasse, A Hollande (1963) Ann. Sci. Natur. Zool. Ser "Les flagelles des genres Holomastigotoides et. Rostronympha". Might as well order it sometime...And now onto a really nice taxonomic summary of parabsalians by Cepicka, Hampl and Kulda 2009 in Protist:Recently revised parabasalian taxonomy.There are now six classes: Trichomonadea, Hypotrichomonadea, Cristamonadea, Tritrichomonadea, Spirotrichonymphea and Trichonymphea. This will be on the final AND your next weekly spelling test. More importantly, this is how they relate:Phylogenetic relationships between the six new classes.Ok, I must run...will definitely get back to parabasalians in much more detail later. Some people in our department happen to be rather obsessed with them, and obsession can be contagious. But for now, feel free to join me in salivating over that really sweet diagram!Right, finals...Source:Cepicka, I., Hampl, V., & Kulda, J. (2010). Critical Taxonomic Revision of Parabasalids with Description of one new Genus and three new Species Protist DOI: 10.1016/j.protis.2009.11.005... Read more »
Cepicka, I., Hampl, V., & Kulda, J. (2010) Critical Taxonomic Revision of Parabasalids with Description of one new Genus and three new Species. Protist. DOI: 10.1016/j.protis.2009.11.005
- April 25, 2010
- 08:28 AM
- 2,211 views
Social onychophorans!
by Psi Wavefunction in Skeptic Wonder
As much as I'm obsessed with protists, I'm a rather promiscuous type when it comes to academic relationships, and thus can find the occasional non-protist cute and interesting. Forgive me if that is 'immoral', but I'm not Christian and thus am not obligated to be intellectually monogamous. So there.Onychophorans (velvet worms) are fucking adorable. Now, whether they are more or less adorable than, say, hypotrich ciliates or Apusomonas proboscidea, is open to debate (I remain loyal to my tribal academic affiliations in that regard), but there's no way you can look at this wonderful creature and not think it's damn cute:Something about onychophoran morphology resonates quite nicely with our innate aesthetic senses...or maybe it's just me. Some of them have really pretty patterns too, or come in absolutely bizarre colours. (Mayer & Herzsch 2007 BMC Evol Biol)A while back someone was waxing poetic about social spiders in class, which led me on quite an adventure. Since I had something very important to do that night, like an exam the following day or something, I got a lot of procrastination done: read about various social spiders (who also have an interesting story of evolutionary dead ends and conflicting levels of selection; oh, and a species with observed cooperative transport of large prey -- apparently fairly rare in arthropods), made my way to social pseudoscorpions (some of them apparently disperse by riding large insects like bugs or beetles), and then I hit upon this paper:Social behaviour in an Australian velvet worm, Euperipatoides rowelli (Onychophora: Peripatopsidae) (Reinhard & Rowell 2005 J Zool)Social behaviour in onychophorans? Seriously!? On a second thought, why the hell not? And then came a complete overload of cute that could've only been enhanced by better images...velvet worms who cuddle!Awww =D Reinhard & Rowell 2005 J ZoolAs cuddly as they may seem, these guys also have a strict social hierarchy involving an alpha female. Reinhard and Rowell (2005) describe a feeding process where a cricket was thrown into the petri dish and attacked by the adult onychophorans (who trap their prey with sticky salivary secretions). After subduing the cricket, the first female fed on the prey for nearly an hour, biting and chasing off any other individual that would approach. After that hour, other females were allowed to feed, and then eventually males and juveniles. Most of the males were feeding after the females left. A feminist's paradise.The interactions between individuals were observed and classified into dominant vs. subordinate: biting and chasing were done by the dominant individual (with the subordinate fleeing) whereas climbing was done by the subordinate and up to the decision of the dominant whether or not to be tolerated:Juveniles were generally left alone and tolerated. Meanwhile, the adults were involved in a constant display of aggression and submission. Females were dominant to the males. When groups of onychophorans from different logs (thus, different social groups) were pairs, individuals of both groups acted aggressively to each other, and despite the males insisting on climbing, no aggregations were formed as they were ruthlessly rejected. Thus, the social groups are stable and at least these onychophorans seem to be capable of kin recognition.The dominance hierarchy seemed largely size-dependent, with smaller females almost always being subservient to the larger individuals. It is believed that as in many other instances of sociality, social behaviour here aids in the cooperative capture of large prey. Curiously, the strict hierarchy when it comes to feeding, with the alpha female hoarding the entire prey, is not known in any other invertebrate.Onychophoran behaviour doesn't receive much attention, perhaps at least partly due to the onychophoran's idea of a perfect habitat not coinciding all too well with that of an ethologist: velvet worms love cold, damp places. So it wouldn't be too surprising if an entire group of social species were eventually discovered, perhaps even with separate origins. In fact, Reinhard and Rowell (2005) state that it is not even known whether sociality may be common for onychophorans in general. On the topic of behaviour, despite their cute and almost fluffy appearance, onychophorans can also be quite vicious. This one devoured a spider bigger than itself:Sticky spit vs. sticky silk. Quite surprisingly, the spit won this battle. (while checking whether this spider actually produces silk, found out that apprently tarantulas secrete adhesive silk from their feet...)It is thought that in order to partake in such complex social behaviours, the onychophoran must have a fairly well-developed region for higher level sensory processing. (considering the complexity of the visual and olfactory cues likely involved in this case, it seems quite plausible. That said, there may well be fairly intricate social interactions out there that do not rely on complex neurology, by executing much simpler rules...) Curiously, they seem to have structures similar to 'mushroom bodies' in arthropods responsible for visual and olfactory processing and regulating complex behaviours. Actually, that was just an excuse to show this stunning image:Onychophoran nervous system. Pseudocoloured to reflect the nerve depth in the confocal projection. Parts of the nervous system arise in a segmented fashion (eg. leg innervation), parts are repeated but not in a segmented way, and they also lack segmental ganglia as those in arthropods. Thus, onychophorans are slightly segmented in some respects, if you will, but still quite different fr... Read more »
Dias, S., & Lo-Man-Hung, N. (2009) First record of an onychophoran (Onychophora, Peripatidae) feeding on a theraphosid spider (Araneae, Theraphosidae). Journal of Arachnology, 37(1), 116-117. DOI: 10.1636/ST08-20.1
Mayer, G., & Harzsch, S. (2007) Immunolocalization of serotonin in Onychophora argues against segmental ganglia being an ancestral feature of arthropods. BMC Evolutionary Biology, 7(1), 118. DOI: 10.1186/1471-2148-7-118
Mayer, G., & Whitington, P. (2009) Neural development in Onychophora (velvet worms) suggests a step-wise evolution of segmentation in the nervous system of Panarthropoda. Developmental Biology, 335(1), 263-275. DOI: 10.1016/j.ydbio.2009.08.011
Reinhard, J., & Rowell, D. (2005) Social behaviour in an Australian velvet worm, Euperipatoides rowelli (Onychophora: Peripatopsidae). Journal of Zoology, 267(01), 1. DOI: 10.1017/S0952836905007090
- April 21, 2010
- 07:02 AM
- 98 views
What songbirds can teach us about language: Does syntactic complexity require selection?
by Psi Wavefunction in Skeptic Wonder
[since I had to write this up elsewhere for a class, might as well double post this here anyway]Here's another story of how alleviated selective pressures can enable increased complexity, without said increase in complexity needing to be driven by positive selection; the paper later relates this to its implications for language evolution:Ritchie & Kirby 2005 Evol Ling Comm Selection, domestication, and the emergence of learned communication systems(Also see Ritchie & Kirby 2007 Emergence of Communication and Language) In a prior study, the Bengalese finch was found to have a more complex song syntax than its wild ancestor (the white-backed munia); furthermore, while the finches could learn the songs of munia, the latter could not effectively learn the complex songs of the finches, suggesting that a part of the capability was physiological. The author of that prior study, Okanoya (2002), argued that the song complexity in the Bengalese finch was driven through sex selection, as the more basic pressures (food and predation) were relieved by domestication, enabling sex selection to finally drive up the complexity; furthermore, this would have been an honest signal of the male’s fitness, as a fitter bird could produce a more complicated song. A competing hypothesis by Deacon agrees that song complexity is kept low in the wild munia through selective pressure, but claims that the lifting of basic selective pressures after domestication enabled the songs to get more complex through other means, namely drift. Thus, processes that previously paled in comparison with the selective pressures against excess song complexity became prominent, such as the effect of songs heard at an early age and mnemonic biases; that is, songs with a more regularised syntax may be easier to recall. Deacon further extends this concept to the evolution of human language; he calls the concept “selective masking”. In short, complexity may arise in the finches’ songs without being driven by direct selective pressure. Ritchie and Kirby set out to test the competing hypotheses through computational modeling; long story short, a bunch of learning filters are set up amid evolutionary models, and the simulation is run trough three phases: 1) Population is filtered to have a particular song type; variation is reduced (modeling the case among wild munia. 2) The population, having learned (and become “attached” to) a particular kind of song, is now bombarded with a bunch of random songs, and demonstrates resistance to be affected much by it: the simulated birds still learn the ‘correct’ song over incorrect ones. 3) Selective pressure is alleviated altogether by simply ceasing to calculate the fitness values. This simulates domestication. Population was once again bombarded with random songs. Complexity was initially defined by Okanoya as the number of unique song notes divided by the number of unique note-to-note transitions (aka ‘Song Linearity’); Okanoya found this ratio to be lower in the Bengalese finches than the wild munia, meaning their songs were more complex (less ‘linear’). Ritchie & Kirby’s simulation also yielded similar results; though they argue that a completely random song would have the maximum complexity by such measures. Additionally, they also used Grammar Encoding Length, or the number of bits required to describe a [in this case, Probabilistic] Finite State Machine, which was used to model song learning. [Now the structural linguistics and information theory loses me completely...]. Turns out, in phase 3, the grammar encoding length did increase and the linearity did go down, supporting the increase in song complexity after domestication. Most importantly, their simulation showed that song complexity can increase in the absense of direct selective pressure, as selection was eliminated altogether in phase 3. This suggests that [once again,] one need not necessarily evoke often-absurdly-complex selection stories (like sex selection and ‘honest signals’) to explain the song complexification in Bengalese finches. Furthermore, these results can be extrapolated further to linguistic evolution, suggesting that perhaps not all of syntax complexification requires selective pressures behind it. In fact, the eliviation of such pressures can allow more complex syntax to arise. As a sidenote, it has been observed that the rise of writing resulted in higher complexity of clause embedding, and this complexity also rose gradually, not immediately after writing systems first appeared (Karlsson in Sampson et al. 2009 Language Complexity as an Evolving Variable). This can also be seen as a case of the lifting (aka ‘masking’) of a selective constraint resulting in allevated complexity, in this case probably not particularly adaptive either. One can convey complex ideas just as well, and in some cases better, without the [ab]use of intricate clausal embedding… Ritchie and Kirby conclude with an idea that perhaps one mustn’t look for selective advantages of elaborate syntax found in human language, but instead investigate what may have prevented syntactic elaboration from arising in the past – what selective pressure may have been alleviated, and what may have caused them?Ritchie GRS, & Kirby S (2007). A Possible Role for Selective Maskingin the Evolution of Complex, LearnedCommunication Systems Emergence of Communication and Language, 387-401 DOI: 10.1007/978-1-84628-779-4_20(Ritchie + Kirby 2005 turns out to be a draft for the 2007 paper, and I'm far too sleepy to reference that properly as it's too complicated...)... Read more »
Ritchie GRS, & Kirby S. (2007) A Possible Role for Selective Masking in the Evolution of Complex, Learned Communication Systems. Emergence of Communication and Language, 387-401. DOI: 10.1007/978-1-84628-779-4_20
- April 12, 2010
- 12:00 PM
- 150 views
In defense of constructive neutral evolution - Part II
by Psi Wavefunction in Skeptic Wonder
Continued from Part I herePart I -Adaptationism vs. Neutralism -"Population genetics ignores reality!" -Existence of neutrality and near-neutralityPart II-Neutral evolution is relevant-Evolution lacks foresight; it can neither anticipate nor respond-Clarifying some terminology: two types of function, positive vs. negative selection-Rise of complexity through non-adaptive means-An example of constructive neutral evolution at work: loss of group I intron self-splicingPart III-Further examples of constructive neutral evolution-Discussion of what sparked this argument: Evolution of ciliate nuclear dimorphismNeutral evolution is relevantAgain, apologies for stating the obvious, but apparently even some prominent evolutionary biologists popularisers of evolutionary biology fail to grasp this simple concept. I've masticated this point to a fine mush by now, but selection and neutral processes act in tandem. Mutational bias and drift matter. So often in the literature you find people arguing over whether something is an adaptation or a spandrel. This gets even more absurd when the structure in question is as massive as the human language capacity. For example, in the landmark Pinker & Bloom 1990 paper signalling the revival of evolutionary linguistics, you find awful sentences like:"The key point that blunts the Gould and Lewontin critique of adaptationism is that natural selection is the only scientific explanation of adaptive complexity." [p.6; emphasis mine]First off, it's kind of cute that a couple psychologists seem to think they can so easily outright dismiss a point made by evolutionary biologists. I mean, seriously, I find it adorable. On that note, I'm now gonna write a book chapter debunking generative linguistics, because, well, my buddy says they're wrong. I wonder how much Pinker's evolutionary views have been shaped by Dawkins et al. Their camp is rather influential outside evolutionary biology, and while many claim that panadaptationism is a strawman -- and even in biology that point is debatable -- outside evolutionary biology, panadaptationism is alive and well. Part of the reason is that adaptationist stories are written in popular books, while pluralistic approaches largely remain hidden in the likes of Molecular Biology & Evolution, Biology Direct and Journal of Molecular Evolution. Researchers working in applied evolutionary fields have likely never heard of them.Back to Pinker & Bloom, first off it's quite a tautology to claim that adaptive complexity evolves through adaptation. Well, yes, you JUST labelled it adaptive. In the immortal words of 4chan, long cat is loooooong. Casting that aside, they've falled for a false dichotomy. You would think someone as smart as Steven Pinker and Paul Bloom wouldn't fall for it. But they did. Why does it have to be one or the other? Why adaptation or spandrel? Especially when we speak of highly complex systems -- is it not in the definition of complexity that they consist of multiple components? How likely is it that all of them are adaptive or neutral or maladaptive? Is it even remotely productive to reduce a system so drastically as to label it simply as an adaptation? What does that even mean, besides stating the obvious? 'Adaptation' has got to be one of the more utterly useless terms in evolution biology, at least the way it's abused today.Letting Pinker & Bloom speak further:"Adaptive complexity" describes any system composed of many interacting parts where the details of the parts' structure and arrangement suggest design to fulfill some function. The vertebrate eye is the classic example. The eye has a transparent refracting outer cover, a variable-focus lens, a light-sensitive layer of neural tissue lying at the focal plane of the lens, a diaphragm whose diameter changes with illumination level, muscles that move it in precise conjunction and convergence with those of the other eye, and elaborate neural circuits that respond to patterns defining edges, colors, motion, and stereoscopic disparity. It is impossible to make sense of the structure of the eye without noting that it appears as if it was designed for the purpose of seeing -- if for no other reason that the man-made tool for image formation, the camera, displays an uncanny resemblance to the eye. Before Darwin, theologians, notably William Paley, pointed to its exquisite design as evidence for the existence of a divine designer. Darwin showed how such "organs of extreme perfection and complication" could arise from the purely physical process of natural selection." [p.6 cont'd]Holy fucking crap, argument from design, for selectionism! Impressive. Yes, you guys just totally pwned Gould with the vertebrate eye. He was unaware of its very existence. Eyes don't preserve well in the fossil record, you see? Eyes look designed, therefore selection. Great. I'll let them finish..."The essential point is that no physical process other than natural selection can explain the evolution of an organ like the eye." [p.6]AFAIK, Gould never denied selection!!! He was a brilliant biologist who thoroughly understood evolution, unlike some recent drama queens. What Gould argues is that a) not everything is an adaptation and b) adaptation is neither the sole nor the most important 'force' in evolution (nor is it actually a 'force' of any sort...). Furthermore, while I am unaware of Gould's opinions about The Eye, and am currently too lazy to research the topic, to me it seems highly implausible that the vertebrate eye evolved solely through selection. In fact, considering that selection is a purifying, not driving, 'force' -- that is, selection simply removes the not sufficiently fit -- it is curious to see where Pinker & Bloom think the 'material' for the selective evolution of the eyes comes from. Surely they're not insane enough to believe that the thing evolved entirely through point mutations each making the eye progressively slightly better and better and suddenly, veeeery gradually, ta-da: The Eye!On that note, I wonder if there's a strong link between selectionism and gradualism. In a sense, one does kind of have to believe the above point-by-point scenario to explain how anything arises purely by selection. To anyone with the slightest inkling of how genes and genomes work, such a view is obviously absurd. Although considering how Dawkins has already enlightened us that molecular biologists may or may not be -reputable- biologists...I'm still amused by how remarkably cute it is of Pinker & Bloom to know so much about the details of evolution that they can make bold statements like the last sentence cited above. That's one strong statement!tl;dr Some rather reputable and smart people still fall for the false dichotomy where something is either purely adaptive or purely 'random'. Selection is not the sole source of order (Lynch 2007 PNAS; you... Read more »
Akins, R., & Lambowitz, A. (1987) A protein required for splicing group I introns in Neurospora mitochondria is mitochondrial tyrosyl-tRNA synthetase or a derivative thereof. Cell, 50(3), 331-345. DOI: 10.1016/0092-8674(87)90488-0
LAMBOWITZ, A., & PERLMAN, P. (1990) Involvement of aminoacyl-tRNA synthetases and other proteins in group I and group II intron splicing. Trends in Biochemical Sciences, 15(11), 440-444. DOI: 10.1016/0968-0004(90)90283-H
Lukes J, Leander BS, & Keeling PJ. (2009) Cascades of convergent evolution: the corresponding evolutionary histories of euglenozoans and dinoflagellates. Proceedings of the National Academy of Sciences of the United States of America, 9963-70. PMID: 19528647
Lynch, M. (2007) Colloquium Papers: The frailty of adaptive hypotheses for the origins of organismal complexity. Proceedings of the National Academy of Sciences, 104(suppl_1), 8597-8604. DOI: 10.1073/pnas.0702207104
Lynch, M. (2007) The evolution of genetic networks by non-adaptive processes. Nature Reviews Genetics, 8(10), 803-813. DOI: 10.1038/nrg2192
Pinker S, & Bloom P. (1990) Natural language and natural selection. Behavioral and brain sciences, 13(4), 707-784. info:/
Stoltzfus, A. (1999) On the Possibility of Constructive Neutral Evolution. Journal of Molecular Evolution, 49(2), 169-181. DOI: 10.1007/PL00006540
- April 12, 2010
- 08:05 AM
- 138 views
Sunday Protist -- Notodendrodes: giant tree forams
by Psi Wavefunction in Skeptic Wonder
Foraminifera are wonderful organisms. For a glimpse of their phylogeny, see this diagram, but keep in mind that the majority of forams are actually allogromiids, forams which build their walls of protein as opposed to scavenged material or depositing mineral substances. From the allogromiids there have been several independent origins of non-proteinaceous forams, many building their tests out of sand grains, remnants of prey or their own waste. Test-building is a complicated and highly regulated process (many forams actually select sand grains with the right properties for building their tests!), a topic I should get around to eventually (not with those dark menacing storm clouds rapidly approaching from the horizon signalling the inevitable Armageddon finals). Thus, I figured that for this superficial protist appreciation post one can't go wrong with Notodendrodes, a genus of forams that look like trees!Notodendrodes, like their sphaerical relative Rhabdammina, build their tests out of sand grains, especially quartz. Unlike Rhabdammina, they also have extensive "root" and "arborescent" structures sticking out of the sphaerical shell and into the sand and up in the air, respectively.Notodendrodes antarctikos from the deep sea, arborescent structure. Image from Bowser lab, shamelessly stolen from certain course slides.One must also note that forams extend far beyond their tests: they are surrounded by a complex network of extruded strands of cytoplasm forming the reticulopodia. These networks can be used to capture prey, absorb nutrients and, in some species, transport algal symbionts far outside the shell to harvest light energy. Notodendrodes lives too deep for housing photosynthetic symbionts; it is said to use its root pseudopodia for absorbing nutrients from the sediment and the arborescent network for sifting through the algal rain falling from the surface (Bowser Lab webpage on Notodendrodes ). Notodendrodes hyalinosphaira. Scalebars: A,B - 2mm; C - 1cm; D - 5mm (DeLaca et al. 2002 J Foram Res)These cells are quite sophisticated and should make great companions for cell biology research. The reticulopodia are able to move things along them (seems to be widespread feature among Rhizarians), and before you get the idea that these giant cells are docile and harmless, some forams can prey on small animals like copepods. There are some truly frightening micrographs in OR Anderson's Biology of Foraminifera. Notodendrodes is apparently uninucleate. Wonder what ploidy levels would be needed to sustain such a monster-sized cell...Anyway, this post fails to do justice to these organisms, but this week is simply awful for me, so I must leave it at that. My whole life is due this week. Also, I have three weeks left to finish wrapping up my current research project, and I'm having great difficulty focusing on it with all the course-related crap on top of it. Expect negligible blogging efforts in the next few weeks...By the way, Mystery Micrograph #20 feels neglected. Do you guys need a few more micrographs for help?Meanwhile, some random foram stuff to look at:Illustrated Glossary of Terms Used in Foraminiferal ResearchPretty SEMs: Forams as Bioindicators: Key tropical and Carribean taxaForam gallery at Microscopy UKBowser Lab page on foramsReferences Bowser, S. (1995). Larger agglutinated foraminifera of McMurdo Sound, Antarctica: Are Astrammina rara and Notodendrodes antarctikos allogromiids incognito? Marine Micropaleontology, 26 (1-4), 75-88 DOI: 10.1016/0377-8398(95)00024-0DeLaca, T. et al. (2002). NOTODENDRODES HYALINOSPHAIRA (SP. NOV.): STRUCTURE AND AUTECOLOGY OF AN ALLOGROMIID-LIKE AGGLUTINATED FORAMINIFER The Journal of Foraminiferal Research, 32 (2), 177-187 DOI: 10.2113/0320177... Read more »
DeLaca, T. et al. (2002) NOTODENDRODES HYALINOSPHAIRA (SP. NOV.): STRUCTURE AND AUTECOLOGY OF AN ALLOGROMIID-LIKE AGGLUTINATED FORAMINIFER. The Journal of Foraminiferal Research, 32(2), 177-187. DOI: 10.2113/0320177
- April 9, 2010
- 07:26 AM
- 208 views
Irremediable Complexity: Notes from Ford Doolittle's seminar talk
by Psi Wavefunction in Skeptic Wonder
While I work on polishing up Part II of the Neutral Evolution series, thought I'd write up and post my four pages of notes from Ford Doolittle's seminar talk today yesterday, while I can still remember what my scribbles were supposed to mean. As there's no unpublished data there, and a long-awaited paper on the subject has just been submitted, I believe it should be fair game for blogging. Coming from a vicious field (Arabidopsis, sigh...), I'm generally rather cautious about blogging department talks and such, but Constructive Neutral Evolution is a subject in need to spreading, and not a particularly competitive area at the moment...Rosie has another summary of today's yesterday's talk, with an executive summary therein; she tried to scoop me, so clearly this means I must outdo her in length and verbosity =P[If anything doesn't make sense, it's very likely an error on my part]-----Irremediable Complexity - Ford Doolittle, 07 Apr 2010[paraphrased from notes; own comments in grey]- Is each step in the evolution of a complex machine useful?Irremediable complexity involves three factors: Tinkering, small populations, ratchets (Constructive Neutral Evolution). [prior to that, must discuss common views on complexity first]Common views on complexity- Directionality: 19th century - divine forces guide evolution; 20th century - orthogenesis - evolution exhibits a drive towards perfection (and complexity)- Progress: Life started off being simple and became increasingly complexBut is there necessarily a trend?(Gould 1996 Full House) The Drunkard's Walk: if one starts off at a limit that cannot be passed, random steps will eventually lead away from this limit. Presumably, life began more or less at the lower limit of complexity (specialised parasites aside), so it's bound to get more complex as it's the only way to go.In fact, complexity is increased only in a few lineages, which also happen to be the ones we really like to look at.So is the evolution of multicellular animals and plants from choanoflagellate-like and chlamydomonas-like organisms, respectively, a drunkard's walk or driven by something (eg. selection)?Selectionist explanations- Accumulation of specific adaptations results in complexity (eg. The Eye)Another example: larger genome size is an adaptation for more gene regulation which is required in more complex organisms. [Note: C-value paradox, etc] Molecular biologists have an obsession with 'mystery DNA' having regulatory roles...- Arms races, sexual selectionGreater biodiversity/more competition between organisms stimulates greater complexity, eg through niche specialisation and sex selection- Evolving evolvabilityOutdoing one's environmental changes by evolving faster. Eg. Exon shuffling as a function of introns: introns space out exons allowing more novel combinations of these exons to occur, which may be adaptive.Caveat with evolvability -- it's a clade-selection level trait, not individual level.Neutral forces - should be our null hypotheses- Tinkering (François Jacob) -- will still have traces of an apparatus' past functions along with new ones -- life is full of Rube Goldberg machines.- Small population size -- mildly deleterious traits more likely to be fixed in smaller populations (Michael Lynch; more info in Part I of my Neutral Evolution series) Eukaryotes are a case of smaller population size relative to prokaryotes.- Ratchets -- 1. Maynard-Smith & Szathmary's Major Transitions; 2. Stoltzfus & Covello's Constructive Neutral EvolutionMajor Transitions: There are steps in evolution that are difficult or impossible to reverse -- act as ratchets.Constructive Neutral Evolution: a previously fortuitous (non-functional) interaction can enable an otherwise-deleterious mutation to occur, resulting in a dependency upon this interaction. [a diagram is in the making]More interactions evoke more opportunity for Constructive Neutral Evolution to drive (via ratchetting) an increase in complexity. [thus, the result would be an explosion of complexity past a certain threshold]The dependency can be built up by other mutations, thus further solidifying the requirement for a given interaction.Note that no positive selection is required at any step [only purifying], would also be more drastic in smaller populations where more deleterious mutations are fixed by drift. That said, positive selection can still play a role in parallel.Examples:Lambowitz's maturase-requiring group I self-splicing intron. [will be discussed in further detail in impending post] A derived Neurospora lineage requires a maturase for the splicing of group I introns whereas nearby relatives do not. Lambowitz later (2006) argues that maturase-mediated splicing evolved in response to the splicing problem, as opposed to enabling it to arise. This is putting the cart before the horse.kDNA editosome (Trypanosomes et al.) [Can be summed up in one interjection: whyyyyyyyyyyyyy???]In summary, genes coded by the mitochondrial genome are non-sensical, and right after transcription the pre-mRNAs are edited by the complicated process involving templates and inserting various U's where they are needed.There are several explanations that have been proposed:- relic of the RNA world -- for starters, tryps are derived. - to correct pre-existing mutations -- backwards logic again (cart before the horse)- regulation[Digression to discuss the two oft-conflated meanings of function]1. Selected function -- how a trait got to be there2. Current function -- what happens if trait is removedExample from Maynard-Smith: Stiff back of the horse. Removal thereof would prevent humans from riding it, but no one can argue that the horse's back evolved so that humans could ride it in the future!How editing really arose -- CNE [see Stoltzfus 1999 JME and Lukes et al 2009 PNAS(and subsequent correspondence)]: once the process started, it couldn't be reversed, thus complexity reached an absurd level."Absurdly complex spliceosome"- if you think about it, it's "incredibly stupid" to have such a complex machine for removing introns- cites "Five Easy Pieces" Sharp 1991 Science laying out a hypothesis for the evolution of group II introns- see Lambowitz example for how the spliceosome may have arisen through initially-neutral protein interactionsRibosomeAlso by CNE. Roughly put, the RNA does most of the enzymatic work in the ribosome, with the proteins taking on more of a structural function. Presumably, initially the ribosome could've been entirely a ribozyme, picking up various proteins for supporting structural roles, like the Lambowitz intron, with the help of constructive neutral evolution.Cited TW O'Brien 2003 IUBMB Life paper: the mammalian mitochondrial ribosome is smaller than that of its host (eukaryotic) yet larger than the prokaryotic counterpart; furthermore, many of the extra mitochondrial ribosomal proteins do not come from the eukaryote! This is a great example of convergence between the two separate... Read more »
O'Brien, T. (2003) Properties of Human Mitochondrial Ribosomes. IUBMB Life (International Union of Biochemistry and Molecular Biology: Life), 55(9), 505-513. DOI: 10.1080/15216540310001626610
Sharp PA. (1991) "Five easy pieces". Science (New York, N.Y.), 254(5032), 663. PMID: 1948046
Stoltzfus, A. (1999) On the Possibility of Constructive Neutral Evolution. Journal of Molecular Evolution, 49(2), 169-181. DOI: 10.1007/PL00006540
- March 31, 2010
- 06:16 AM
- 101 views
In defense of constructive neutral evolution - Part I
by Psi Wavefunction in Skeptic Wonder
Caution: What follows is mostly an opinion piece by an undergrad. While said undergrad has done a fair amount of reading on the topic, the post is still subject to many errors. Tread carefully. [/disclaimer]I won't go into an all-out discussion of neutral evolution here: I'm neither qualified enough nor have enough spare time at the moment. However, some issues seem to crop up multiple times, both here and on other blogs. I figured I'd try to briefly adress some of them, although do take my discussion with a grain of salt. That said, while neutral theory require a certain amount of effort to grasp properly (just like any other aspect of evolutionary biology), it is not something worth dismissing. In fact, if you consider how horribly misunderstood evolutionary biology is on the whole (even among grad students: Gregory & Ellis 2008 BioScience), the neutral elements of evolution seem to be understood by a very small fraction of biologists even.Perhaps part of the problem is that adaptive evolution is just...flashier. It makes for fun and fairly simple stories: Eg. the peacock has a huge tail to signal to the females that it has nice genes that would compensate for the problems it causes. This "Good Genes" theory is actually taught in first year curricula, and makes very little sense upon further examination, and definitely does not survive Occam's Razor. A simpler explanation would, of course, entail something like runaway sexual selection (ie. female happened to prefer flashy tail, males with flashier tails outcompete their dimmer counterparts, tail gets longer) or that the tail may have a more important function, like scaring away predators. In any case, the adaptive approach very often results in what is mostly a story-telling exercise, and one that is very difficult to deal with experimentally. Worst of all, those stories very easily make sense upon first glance, and thus the field becomes cluttered with poorly thought out theories that sound reasonable.This post became way too long, so I broke it up into three parts; table of contents here:Part I-Adaptationism vs. Neutralism-"Population genetics ignores reality!"-Existence of neutrality and near-neutralityPart II-Neutral evolution is relevant-Evolution lacks foresight; it can neither anticipate nor respond-Rise of complexity through non-adaptive means-Further examples of constructive neutral evolutionPart III-Discussion of what sparked this argument: Evolution of ciliate nuclear dimorphismAdaptationism vs. NeutralismOf course, none of what I said is new by any margin: the famous Gould and Lewontin 1979 Spandrels of San Marco (free access) paper does a nice job at pointing out many of the fallbacks of panadaptationism. And I don't find it much of an 'attack', as it is often described by diehard adaptationists, but perhaps that's just me. Since so many before me have pointed out the fallbacks of the 'adaptationist programme', I won't bother dwelling on it any further. Besides, this type of thing causes a great polarising effect on the community, with people being either hardcore adaptationists or hardcore neutralists. This seriously fucks up any progress on the topic, because biology hardly tolerates dichotomies. In fact, the truth in this case does not even lie 'somewhere in the middle', but in the fact that both adaptive and neutral processes work in tandem.Let me reiterate that: Selective and neutral mechanisms work in tandem. Simultaneously. In some situations (eg. large effective population sizes, in bacteria; Lynch 2007 PNAS, Yi 2005 Bioessays), adaptive processes are more dominant; in some cases, adaptive 'forces' are negligible compared to neutral phenomena (small effective population sizes). Considering some specific structure, parts of its evolutionary history have been driven more by drift and mutational bias, interspersed with parts dominated by selective pressures. It's not like selection takes a nap for a while, and then gets back to work while drift, bias et al. chill out. There is no point to dismiss one or the other, like so many tend to do.Curiously, I've heard numerous times that "Well, maybe selection is less important for bacteria, but it is the dominant force in vertebrates". How hilarious is it that any population geneticist will tell you the exact opposite: bacteria are under overwhelming selective pressure due to their freaking massive effective pop sizes, meaning that drift is much less effective in that situation relative to selection. Vertebrates are actually an awesome example of selection going rather easy: being a large multicellular thing with a backbone is a damn stupid way to copy your genes. Seriously!Now, you may wonder why should anyone who's not an evolutionary biologist care about any of this? For a cell or developmental biologist, why not assume everything is there for a reason?Because this leads to rather convoluted explanations for things. Take signalling pathways, for example. Is there any particular reason you have tens of genes required to turn on a particular behaviour in the end when you could've 'designed' it instead to use only one or two? Here we have again a problem with the adaptationist approach: you can pretty much always think of some reason why something is 'useful' or adaptive. That doesn't make it right. What if some features of these pathways originally evolved as a form of adaptively-neutral 'bloating' of the system? See Lynch 2007 PNAS, Lynch 2007 Nature Rev Genet for more on non-adaptive processes in evolution of genetic pathways. (Or just stop reading this post and go through this short list instead ;-))."Population genetics ignores reality!"Now, there's some complaints that popgen kind of fails at taking reality into account. For some work in the field, that is true -- just like in any other field. Did you seriously think everyone, to the last moron, is in touch with reality in your field? If so, I'd love to hear! (no philosophers need apply, heh... although to be fair, there are some 'fringe lunatics' there who actually make sense by our standards.) That said, mathematical modeling requires simplifications to be made to get somewhere. If you have a problem with that, note all those humanities scholars who are sneering at us because we make simplifications as scientists! They wisely take the easy way out and conclude that reality is a social construct and understanding is actually impossible and thus not worthy losing sleep over...Good mathematical biologists note their simplifications, keep track of them, and know when to simplify what, and what the limitations of their models are. Even better mathematical biologists test their models empirically, thereby producing work that is truly relevant to the rest of us. In my [admittedly still quite inexperienced] opinion, Michael Lynch belongs to that category. Seriously, I despised and dismissed the entire field of population genetics as well, and thanks to some of his papers realised it's probably not a very good idea to do that. In a field as messy as biology, any tidbit of information, even if it comes from simulations, is not only valuable, but essential to the very hope of sorting stuff out. We, that is -- all biologists -- are in no position to discard entire fields because of our petty tribalistic snobbery. Tread with caution -- yes. Dismiss without a second thought -- absolutely not.Existence of neutrality and near-neutralityTo touch on the existence of 'true' neutrality, let me show you a few diagrams. The first one outlines the history of selectionist and neutral theories:... Read more »
Bernardi, G. (2007) The neoselectionist theory of genome evolution. Proceedings of the National Academy of Sciences, 104(20), 8385-8390. DOI: 10.1073/pnas.0701652104
Gregory, T., & Ellis, C. (2009) Conceptions of Evolution among Science Graduate Students. BioScience, 59(9), 792-799. DOI: 10.1525/bio.2009.59.9.11
Lynch, M. (2007) Colloquium Papers: The frailty of adaptive hypotheses for the origins of organismal complexity. Proceedings of the National Academy of Sciences, 104(suppl_1), 8597-8604. DOI: 10.1073/pnas.0702207104
Lynch, M. (2007) The evolution of genetic networks by non-adaptive processes. Nature Reviews Genetics, 8(10), 803-813. DOI: 10.1038/nrg2192
Ohta, T. (1992) The Nearly Neutral Theory of Molecular Evolution. Annual Review of Ecology and Systematics, 23(1), 263-286. DOI: 10.1146/annurev.ecolsys.23.1.263
Ohta, T. (2002) Inaugural Article: Near-neutrality in evolution of genes and gene regulation. Proceedings of the National Academy of Sciences, 99(25), 16134-16137. DOI: 10.1073/pnas.252626899
Stoltzfus A. (1999) On the possibility of constructive neutral evolution. Journal of molecular evolution, 49(2), 169-81. PMID: 10441669
Yi, S. (2006) Non-adaptive evolution of genome complexity. BioEssays, 28(10), 979-982. DOI: 10.1002/bies.20478
- March 30, 2010
- 06:47 AM
- 90 views
MM17 Answer - Spironucleus: double cells with twisted nuclei
by Psi Wavefunction in Skeptic Wonder
Really need to take care of the long lineup of overdue Mystery Micrographs. And clean up a bit of this huge drafts pile that has accumulated lately. Because I'm lazy, let's do Spironucleus first, from MM17. It goes well with laziness as not very much is known about it, which means there isn't too much to write about it. Shit, now you know why I blog about obscure organisms like those various protists...my secret is out!SEMs of diplomonad fish parasite Spironucleus vortens. cr - compound lateral ridge.lpr + rpr - left and right peripheral ridge, respectively. Note their rope-like form. pp - posterior papillum. Note flagellar pockets in (4). r - recurrent flagellum. 5 - an atypical specimen with transposed posterior structures. 6 - laterla view of posterior end. A fairly complicated flagellate! (Sterud & Poynton 2002 JEM)To clarify the complicated morphology:Drawings of the 'double-celled' Spironucleus vortens. The two recurrent flagella pass inside the cell and emerge at the posterior end. (Poynton et al. 1995 JEM)Spironucleus may strike you as being particularly symmetrical. In fact, it very well is a 'double cell', containing two nuclei (slightly wrapping around each other helically, hence Spironucleus), and two sets of flagella. The path of the recurrent flagella makes sense when considering that the single cells of the group have three flagella pointing one way, and the fourth pointing another. These double cells are case of the two cells being 'stuck together' at the side of the recurrent flagellum. Here's a TEM to show the elongate nuclei and the flagella passing between them:Top: longitudinal section at the anterior end of the flagellate. n - nuclei; k - kinetosomes. Bottom: cross-section of the anterior end. Note the recurrent flagella (r; circled in red) passing between the nuclei. (Poynton et al. 1995 JEM)Here's another species of Spironucleus, S.berkhanaus, in arctic char blood:Parasitic Spironucleus barkhanus in the blood of arctic char, as well as in isolation. Note that it's a different species from the one above, which may explain the lack of lateral ridges.(Sterud et al. 2003 Dis Aquatic Organisms)Note how the two species seem a bit different from each other. This shows the morphological diversity in the group. In fact, Spironucleus seems to be a bit polyphyletic or paraphyletic at best (Jørgensen & Sterud 2007 Protist; Kolisko et al. 2008 BMC Evol Biol).Phylogeny of Spironucleus. This poor genus seem to be ruthlessly strewn all over Diplomonadida. Note position of S.vortens and S.berkhanus. (Jørgensen & Sterud 2007 Protist)Diplomonads have an interesting tale involving cell cycle defects and duplications of the nucleus and flagella, but I'll leave you in suspense for a while. That's a bigger topic, and I should probably introduce our cute friend Giardia first (cute friend in SEM, and horrible foe in the intestine...). Giardia is a independent case of cell 'doubling', and is organised quite differently. Further discussion of diplomonads should happen...eventually. Feel free to nag me about it if you're really interested!ReferencesJORGENSEN, A., & STERUD, E. (2007). Phylogeny of Spironucleus (Eopharyngia: Diplomonadida: Hexamitinae) Protist, 158 (2), 247-254 DOI: 10.1016/j.protis.2006.12.003... Read more »
JORGENSEN, A., & STERUD, E. (2007) Phylogeny of Spironucleus (Eopharyngia: Diplomonadida: Hexamitinae). Protist, 158(2), 247-254. DOI: 10.1016/j.protis.2006.12.003
POYNTON, S., FRASER, W., FRANCIS-FLOYD, R., RUTLEDGE, P., REED, P., & NERAD, T. (1995) Spironucleus vortens N. Sp. from the Freshwater Angelfish Pterophyllum scalare: Morphology and Culture. The Journal of Eukaryotic Microbiology, 42(6), 731-742. DOI: 10.1111/j.1550-7408.1995.tb01625.x
Sterud E, Poppe T, & Bornø G. (2003) Intracellular infection with Spironucleus barkhanus (Diplomonadida: Hexamitidae) in farmed Arctic char Salvelinus alpinus. Diseases of aquatic organisms, 56(2), 155-61. PMID: 14598991
STERUD, E., & POYNTON, S. (2002) Spironucleus vortens (Diplomonadida) in the Ide, Leuciscus idus (L.) (Cyprinidae): a Warm Water Hexamitid Flagellate Found in Northern Europe. The Journal of Eukaryotic Microbiology, 49(2), 137-145. DOI: 10.1111/j.1550-7408.2002.tb00357.x
- March 28, 2010
- 03:49 AM
- 181 views
Sunday Protist -- Trichotokara nothriae: Guitar-shaped gregarine
by Psi Wavefunction in Skeptic Wonder
This post turned into a bit of a hodgepodge of various gregarine-related trivia. Proceed with caution.Gregarines are a group of apicomplexans (='Sporozoa', a vastly diverse group famous for the malarial parasite Plasmodium and the behaviour-altering Toxoplasma) characterised by a monoxenous (single host) lifestyle that is quite different from that of other 'apis'. Christopher Taylor wrote a nice post about them here.Apicomplexa are alveolates along with ciliates and dinoflagellates; you can find them on the left side of this tree . The apicomplexan phylogeny is a complete mess at the moment; the old coccidian-haematozoan-gregarine divisions aren't too well-supported and the relationships of stuff within them are even murkier. As an aside, many apis have an 'apicoplast', or a relic plastid of red algal origin -- their ancestors were once photosynthetic! In fact, a paraphyletic group of organisms basal to apicomplexa (Chromera et al.) are currently photosynthetic, further supporting the photosynthetic ancestry of these weird mostly-intracellular parasites, most of whom rarely ever see the light of day!Gregarines are typically invertebrate parasites and unlike other apicomplexans, tend to spend most of their lives extracellularly; in fact, their cellular penetration consists of attaching themselves to a cell via the mucron (holdfast-like structure). You can read more about their biology and life cycle on their ToLWeb page. (also a review in Tr Parasitol: Leander 2007) If you want to see some for yourself, kidnapping and slicing up an earthworm is an easy way to do so: Monocystis is a parasite of earthworm seminal vesicles (feeds on sperm), and a rather abundant one. It may actually be quite easy to find various apicomplexan parasites in insects -- it is estimated that most of them may have an api specialised in parasitising them, which hints at the total apicomplexan diversity being something outrageously vast! Such a project would also be a good excuse to learn insect anatomy, which I find to be quite complicated.Right, you wanted to see a new genus of guitar-shaped gregarines: Trichotokara from the intestine of an onuphid tubeworm. a-e: trophozoites (feeding forms). M - mucron ('holdfast'), CB - cell body. Arrow - junction between mucron and cell body, which can be seen extending further into the mucron in (e; arrowheads). f: gamonts in syzygy, or gregarine sex. Scalebars: a-e 10um; f 25um. (Rueckert & Leander 2010 J Invert Pathol)By the way, if anyone asks you for a six-letter word in English 'devoid of any vowels', keep 'syzygy' in mind. Technically it does have vowels, as any phonologist would tell you, but most people insist on equating letters with sounds, and y 'is not a vowel'. Regardless, it's still a really awesome word. Syzygy!More gregarine awesomeness. Note how the cell surface seems to strive for increased surface area, especially in the mucron which gets inserted into a cell:SEM of Trichotokara. b - close-up of hair-like projections of the mucron. c - junction between mucron and cell body. d - folds along the cell body. Scalebars: a - 10um; b-d - 1um. (Rueckert & Leander 2010 J Invert Pathol)This gives me an excuse to mention a paper on proximate vs. ultimate convergence by the senior author on the above gregarine paper: Leander 2008 JEM (free access). Among several other examples of ultimate convergence between multicellular and unicellular organisms inhabiting similar environments, gregarines and nematodes are compared in terms of their structural organisation. While nematodes have longitudinal muscles just beneath the elastic epidermis, gregarines have subpellicular bands of longitudinal microtubules running just underneath the elastic cortex (although used differently -- see gliding motility below). Curiously, in both cases the result is a sinusoidal (wiggling) pattern of movement. Additionally, tapeworm and Haplozoon (dinoflagellate) surface morphology are noted to be similar (covered with microvili), for the obvious purpose of increasing surface area. It's probably not much of a stretch to add gregarine surface structure to that list. (see Leander et al. 2003 J Parasitol for more gregarine surfaces) Interesting case of structural ultimate convergence between nematodes and gregarines. Purple - bands of muscle and microtubules, respectively. Blue - elastic epidermis and tri-layered cortex, respectively. The three cortical layers consist of the plasma membrane at the very surface, with two alveolar membranes immediately below. (Leander 2008 JEM)Before we proceed to a digression on apicomplexan motility, oblicatory phylogeny of Trichotokara and relatives. Note its extremely diverged SSU sequence resulting in a hellishly long branch:ML tree of SSU rDNA sequences. Probably wouldn't trust its exact placement among the gregarines just yet... (Rueckert & Leander 2010 J Invert Pathol)Apicomplexans are generally aflagellate in their trophic stage (I say 'generally' just in c... Read more »
Baum, J., Papenfuss, A., Baum, B., Speed, T., & Cowman, A. (2006) Regulation of apicomplexan actin-based motility. Nature Reviews Microbiology, 4(8), 621-628. DOI: 10.1038/nrmicro1465
G. E. Gates. (1926) Preliminary Note on a New Protozoan Parasite of Earthworms of the Genus Eutyphœus. Biological Bulletin, 51(6), 400-404. info:/
LEANDER, B. (2008) Marine gregarines: evolutionary prelude to the apicomplexan radiation?. Trends in Parasitology, 24(2), 60-67. DOI: 10.1016/j.pt.2007.11.005
LEANDER, B. (2008) A Hierarchical View of Convergent Evolution in Microbial Eukaryotes. Journal of Eukaryotic Microbiology, 55(2), 59-68. DOI: 10.1111/j.1550-7408.2008.00308.x
Molino, P., & Wetherbee, R. (2008) The biology of biofouling diatoms and their role in the development of microbial slimes. Biofouling, 24(5), 365-379. DOI: 10.1080/08927010802254583
Purvis, A., & Hector, A. (2000) Getting the measure of biodiversity. Nature, 405(6783), 212-219. DOI: 10.1038/35012221
Rueckert, S., & Leander, B. (2010) Description of Trichotokara nothriae n. gen. et sp. (Apicomplexa, Lecudinidae) – an intestinal gregarine of Nothria conchylega (Polychaeta, Onuphidae). Journal of Invertebrate Pathology. DOI: 10.1016/j.jip.2010.03.005
Soldati, D., & Meissner, M. (2004) Toxoplasma as a novel system for motility. Current Opinion in Cell Biology, 16(1), 32-40. DOI: 10.1016/j.ceb.2003.11.013
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