Bioavailability = solubility (for the most part) To discuss heavy metals (lead, nickel, mercury, cadmium, silver, copper, and so on) and how they can be detrimental to the environment or toxic to people, plants, or animals, we have to first posses a vague understanding of bioavailability and bioaccessibility. These terms describe whether or not the [...]... Read more »
SAYER, J., RAGGETT, S., & GADD, G. (1995) Solubilization of insoluble metal compounds by soil fungi: development of a screening method for solubilizing ability and metal tolerance. Mycological Research, 99(8), 987-993. DOI: 10.1016/S0953-7562(09)80762-4
Marc Kirschner pointed me to this interesting recent paper about the evolvability of proteins (Philips et al. 2010. Robustness and evolvability in the functional anatomy of a PER-ARNT-SIM (PAS) domain, PNAS PMID: 20889915). What’s evolvability? It’s a term used to indicate the qualities of a molecule or organism that allow it to evolve effectively; the [...]... Read more »
Philip AF, Kumauchi M, & Hoff WD. (2010) Robustness and evolvability in the functional anatomy of a PER-ARNT-SIM (PAS) domain. Proceedings of the National Academy of Sciences of the United States of America, 107(42), 17986-91. PMID: 20889915
Last Friday I wrote about a new study by paleontologist Phil Senter that revised the arrangement of bones in the front feet of Stegosaurus. Despite being only a distant relative of the sauropod dinosaurs, Stegosaurus had convergently evolved a semi-circular pattern of bones which would have given it semi-tubular forefeet similar to that of sauropods [...]... Read more »
Senter, P. (2010) Evidence for a sauropod-like metacarpal configuration in ankylosaurian dinosaurs. Acta Palaeontologica Polonica. DOI: 10.4202/app.2010.0041
Describes a gene encoding a protein in the neurexin family, Caspr2, that's involved in myelination and distribution of ion channels along axons. Disruptions of this gene have been associated with autism, epilepsy, Tourette syndrome, intellectual disability, schizophrenia and other neurodevelopmental disorders.... Read more »
Arking, D., Cutler, D., Brune, C., Teslovich, T., West, K., Ikeda, M., Rea, A., Guy, M., Lin, S., & Cook Jr., E. (2008) A Common Genetic Variant in the Neurexin Superfamily Member CNTNAP2 Increases Familial Risk of Autism. The American Journal of Human Genetics, 82(1), 160-164. DOI: 10.1016/j.ajhg.2007.09.015
Bakkaloglu, B., O'Roak, B., Louvi, A., Gupta, A., Abelson, J., Morgan, T., Chawarska, K., Klin, A., Ercan-Sencicek, A., & Stillman, A. (2008) Molecular Cytogenetic Analysis and Resequencing of Contactin Associated Protein-Like 2 in Autism Spectrum Disorders. The American Journal of Human Genetics, 82(1), 165-173. DOI: 10.1016/j.ajhg.2007.09.017
Poliak S, Gollan L, Martinez R, Custer A, Einheber S, Salzer JL, Trimmer JS, Shrager P, & Peles E. (1999) Caspr2, a new member of the neurexin superfamily, is localized at the juxtaparanodes of myelinated axons and associates with K channels. Neuron, 24(4), 1037-47. PMID: 10624965
Poliak, S., & Peles, E. (2003) The local differentiation of myelinated axons at nodes of Ranvier. Nature Reviews Neuroscience, 4(12), 968-980. DOI: 10.1038/nrn1253
Much of my work involves studying fish genomes. Over time I've gotten to know them pretty well and I can only conclude that fish are incredible and inordinately interesting creatures. Unfortunately fish have an undeservedly low standing in the eyes of the general public, as well as many researchers in more mammal-oriented fields, often being referred to as "lower vertebrates" in the great evolutionary story that led to "higher vertebrates" like mammals. In fact, more than half of all vertebrate species are fish, not "higher vertebrates", and fish encompass the great majority of all vertebrate diversity. In most senses fish are the "typical" vertebrates. Their origin set the whole stage for vertebrate development, anatomy and physiology and the fair view of vertebrate evolution should be that reptiles, birds and mammals, basically everything that lives on land, are a subgroup of highly specialized fish, an interesting "side-step" rather than the "crown" of evolution.
So why this preface in defense of fish? I have found a little story that more than anything I've read lately highlights the deep connection between fish and mammals and does a very good job at blurring the distinction between what's considered typically mammal and what fish are capable of. Plus, it relates to my own research.
Discus fish (Symphysodon aequifasciatus). Ref: Flickr.
Behold the discus fish.
The three discus fish species of the Amazon basin in the genus Symphysodon are something out of the ordinary in that they exhibit parental care behaviors and feed their fry with a special mucus secreted from both parents' skin. The fry start nibbling from the parents' skin a few days after hatching and continue for a up to 3 weeks before being "weaned off", in a phenomenon akin to mammal lactation. Not only does the composition of the mucus change as the fry grow in a way that mirrors the changes in the composition of milk in mammals, it also seems that there are shared mechanisms in the stimulation of discus fish mucus production and milk production in mammals. Discus fish are not the only fish species that have these qualities, but they have become the typical example, not least because they have been appreciated as aquarium fish for a long time. You can find and abundance of videos showing discus fish parental behaviors on YouTube.
The composition of non-parental skin mucus and parental skin mucus in discus fish is different. During breeding the mucus contains many antimicrobial proteins and factors that stimulate the regeneration of skin cells; this is to protect the parents from infections due to the fry's excessive nibbling. But the mucus also contains antibodies and factors that are thought to contribute to the fry's immunity during the very first period of life, akin to mammal milk. In another parallel, the levels of antibodies and proteins are at their peek around the time of hatching (birth) and decrease when it's time for "weaning".
In mammals the hormone prolactin, as the name indicates, regulates the production of milk through the prolactin receptors that are expressed on milk gland cells. However prolactin is a very old hormone (fish have prolactin too!) and probably the hormone that has the most known functions in all of endocrinology. In fish it mostly acts on the gills, the intestines and the kidneys to control the regulation of water balance in the body. This is probably one of the original roles of prolactin in the first vertebrates a few hundred million years ago. However, in both mammal and fish, including the discus fish, prolactin has been shown to stimulate parental care indicating that the effect on behavior also is old. Lactation on the other hand seems to be a relatively new function for prolactin and thus the name "promotor of lactation" is a misnomer if there ever was one. Or is it?
Ref: Khong et. al. (see reference below)
Studies of the expression of the prolactin receptor in the discus fish skin reveal that it's expressed in significantly increased numbers during the parental phase, as you can see in the figure above, indicating that it's prolactin that stimulates mucus production! What an incredible parallel! It's the closest thing to breast-feeding fish that you will ever find. The prolactin receptor also seems to mediate the creation of new mucous cells in the skin, further increasing mucus production and counteracting the effects of the fry's nibbling. The mucous cells of the skin are a kind of epithelial cells, so are the milk gland cells in mammals and the sweat gland cells that they share an origin with. So are the cells in the fish intestine and gills that are involved in water balance regulation. Do you see the pattern? Milk secretion, mucus secretion, sweating, the transport of water across a barrier are variants on the same theme.
The similarities between mammal lactation and discus fish parental mucus production could all be incidental, the result of convergent evolution, but the involvement of prolactin receptors in both processes speaks for there being a deep ancestral mechanism shared between lactation in mammals and mucus production in fish.
Buckley, J., Maunder, R., Foey, A., Pearce, J., Val, A., & Sloman, K. (2010). Biparental mucus feeding: a unique example of parental care in an Amazonian cichlid Journal of Experimental Biology, 213 (22), 3787-3795 DOI: 10.1242/jeb.042929
Khong, H., Kuah, M., Jaya-Ram, A., & Shu-Chien, A. (2009). Prolactin receptor mRNA is upregulated in discus fish (Symphysodon aequifasciata) skin during parental phase. Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 153 (1), 18-28 DOI: 10.1016/j.cbpb.2009.01.005
... Read more »
Buckley, J., Maunder, R., Foey, A., Pearce, J., Val, A., & Sloman, K. (2010) Biparental mucus feeding: a unique example of parental care in an Amazonian cichlid. Journal of Experimental Biology, 213(22), 3787-3795. DOI: 10.1242/jeb.042929
Khong, H., Kuah, M., Jaya-Ram, A., & Shu-Chien, A. (2009) Prolactin receptor mRNA is upregulated in discus fish (Symphysodon aequifasciata) skin during parental phase. Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 153(1), 18-28. DOI: 10.1016/j.cbpb.2009.01.005
A couple weeks ago, I wrote about a study involving mice...and circadian rhythms: too much low light (day or night ) or insufficient bright light (during the day) can mess with circadian rhythms and cause bodily fatigue, jet lag, seasonal effective disorder, whatever you want to call it. It made me glad I walk to work in the bright sunshine every day and sad that my bedroom wall has big floor-to-ceiling windows.
This week, I read another study involving hamsters...and circadian rhythms: too much low light at night causes specific changes in the brain AND symptoms of depression (i don't know how precise you can get at judging whether a hamster is depressed.) Researchers exposed one group of the furry fellow to low light every night for 8 weeks, and found the hamsters hippocampus changed, though there was no change in the level of cortisol, a stress hormone. That made researchers pretty sure the changes were a result of the light and not the lab conditions. In the hippocampus, scientists actually observed fewer hairlike growths, used to make chemical connections, on brain cells.
Both studies are quick to relate extreme fatigue and depression to low light exposure during the night. I wonder if this will pan out in clinical tests of humans. If so, I'm gonna totally rethink my sleeping schedule, buy some blackout curtains, and never take the red-eye.
Altimus CM, Güler AD, Alam NM, Arman AC, Prusky GT, Sampath AP, & Hattar S (2010). Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities. Nature neuroscience, 13 (9), 1107-12 PMID: 20711184 casey on twitter click here... Read more »
Altimus CM, Güler AD, Alam NM, Arman AC, Prusky GT, Sampath AP, & Hattar S. (2010) Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities. Nature neuroscience, 13(9), 1107-12. PMID: 20711184
Postdoc Gio da Silva is our Featured Scientist of the Month. Read on to find out more about his passion for the sciences and love of teaching as well as valuable tips about choosing a Postdoc lab and maintaining organization in the lab.... Read more »
Tay WM, Epperson JD, da Silva GF, & Ming LJ. (2010) 1H NMR, mechanism, and mononuclear oxidative activity of the antibiotic metallopeptide bacitracin: the role of D-Glu-4, interaction with pyrophosphate moiety, DNA binding and cleavage, and bioactivity. Journal of the American Chemical Society, 132(16), 5652-61. PMID: 20359222
da Silva GF, Lykourinou V, Angerhofer A, & Ming LJ. (2009) Methionine does not reduce Cu(II)-beta-amyloid!--rectification of the roles of methionine-35 and reducing agents in metal-centered oxidation chemistry of Cu(II)-beta-amyloid. Biochimica et biophysica acta, 1792(1), 49-55. PMID: 19061952
When craftsman Ken Walker decided to reconstruct an Irish elk for the “recreations” category of the 2005 World Taxidermy Championships, he did not rely on bones alone. Skeletons of the extinct Pleistocene mammal – technically called Megaloceros giganteus – were in no short supply as references, but there are some things that bones just can’t [...]... Read more »
ANTÓN, M., GARCÍA-PEREA, R., & TURNER, A. (1998) Reconstructed facial appearance of the sabretoothed felid Smilodon. Zoological Journal of the Linnean Society, 124(4), 369-386. DOI: 10.1111/j.1096-3642.1998.tb00582.x
Gould, S. (1997) The exaptive excellence of spandrels as a term and prototype. Proceedings of the National Academy of Sciences, 94(20), 10750-10755. DOI: 10.1073/pnas.94.20.10750
LISTER, A. (1994) The evolution of the giant deer, Megaloceros giganteus (Blumenbach). Zoological Journal of the Linnean Society, 112(1), 65-100. DOI: 10.1006/zjls.1994.1034
REUMER, J., ROOK, L., VAN DER BORG, K., POST, K., MOL, D., & DE VOS, J. (2003) LATE PLEISTOCENE SURVIVAL OF THE SABER-TOOTHED CAT HOMOTHERIUM IN NORTHWESTERN EUROPE. Journal of Vertebrate Paleontology, 23(1), 260-262. DOI: 10.1671/0272-4634(2003)23[260:LPSOTS]2.0.CO;2
Previously, on NeuroDojo...
(M)igration causes brain size to reduce, rather than the other way around.
The quote might be a bit misleading, though, because that was in reference to bird migration. All manner of animals migrate, and it is possible that birds face pressure other creatures don’t.
A good first place to look for a comparison would be bats. Because despite being separate by several hundred millions years of evolution, bats have one very obvious similarity to birds: they fly. And, like birds, they migrate, though their migration tends to be shorter than birds. So you would expect some of the same patterns of brain size to happen in bats as in birds.
McGuire and Ratcliffe decided to take this a step further, not only looking at overall brain size, but the size of the hippocampus. The hippocampus is deeply involved in learning about your position in space, and it has been shown repeatedly in many species that those with heavier demands on their spatial memory (say, from having a larger home range tend to have a larger hippocampus). You might expect migrating bats to have a larger hippocampus than those that don’t.
One of the recurring problems with trying to figure out these sorts of questions, though, is what data you use. Generally, you can’t go out and get new brains, and do detailed measurements of how much each bat species migrates. You have to go back into published reports on migration.
There are biases both ways: people might not realize a species migrates (bats being nocturnal). And for those bats that don’t migrate, it might not get explicitly mentioned, because it’s “normal” for bats, which means you get no information. And within one species, some individuals will migrate and others won’t. Still, they ended up with a list of over 300 bats species for which they had some brain and behaviour data.
Migrating bats indeed had smaller overall brain sizes for their size – just like the birds. This supports the idea that brains are expensive, and so is flying, and the combination of the two is incredibly difficult to fit into the energy budget.
I’d be interested to see if there were differences in the brains of migrating and non-migrating invertebrates, like butterflies. They tend to have smaller nervous systems relative to their body size than vertebrates, so would they also have the same energetic costs to shave off neurons here and there? Or vertebrates that migrate without flying?
More surprising was that the hippocampus showed no difference between the migrating and non-migrating bats. McGuire and Ratcliffe suggest there are just too many confounding factors for any signal to rise above the noise. What we need are some bat neuroethologists (and I know you’re out there) to do some studies on how bats use the hippocampus in a controlled lab setting.
McGuire L., & Ratcliffe J. 2010. Light enough to travel: migratory bats have smaller brains, but not larger hippocampi, than sedentary species. Biology Letters: In press. DOI: 10.1098/rsbl.2010.0744
Photo (Myotis myotis) by Jan Svetlík on Flickr; used under a Creative Commons license.... Read more »
McGuire L., & Ratcliffe J. (2010) Light enough to travel: migratory bats have smaller brains, but not larger hippocampi, than sedentary species. Biology Letters. DOI: 10.1098/rsbl.2010.0744
Scientists thought they had a pretty good handle on the social interactions of bottlenose dophins (Tursiops). They've used the term fission-fusion dynamics to describe dolphin (and non-human primate) society and so far it has served researchers well. Fission-fusion societies among dolphins are characterized by two levels of social hierarchy: groups of two or three related males ("first-order alliances") which work together to guard one or more females from other males, and larger teams comprised of multiple related first-order alliances ("second-order alliances") which cooperate to "steal" females from other groups. Since the individuals in first- and second-order alliances are related and therefore share genes, this sort of cooperation can be explained by kin selection.
For six years, Richard Connor and his team studied the social interactions among the bottlenose dolphins of a six hundred square kilometer portion of Shark Bay, Australia. In a paper recently published online in Biology Letters, they describe a new third level of social hierarchy among bottlenose dolphins: a set of alliances among second-order alliances, that they describe as second-order "super-alliances" ("third-order alliances"). The groups which combine to form these third-order super-alliances were often comprised of individuals who were not related, and therefore kin selection can not be applied to these relationships.
To test if there was any predictable way in which the different dolphins cooperated with each other, the researchers conducted an analysis on the thirty-four male dolphins on which they had data regarding third-order alliance interactions. It is particularly important to note that all third-order alliance interactions occurred only during conflicts over females and not, for example, during foraging or hunting expeditions.
Results of cluster analysis. Click to enlarge. Groups are WC (green), KS (brown), PD (blue) and RHP (purple).
Consider the following interactions, which were observed in 2002 and 2006. RHP is a first-order alliance of three individuals, PD is a second-order alliance of seven individuals, and KS is a second-order alliance of fourteen individuals.
2002: Three KS males were approached by the seven PD members and the three RHP males. One PD trio had a female and the other took the female from the KS males.
2006: Four KS males attacked three PD males with a female and immediately the four other PD males and seven of the eight KS males in the area joined the group for totals of seven PD males and eleven KS males. One of the KS trios that joined had a female throughout the skirmish. Aggression (vocalizations and movement) escalated 20 min later when two RHP males (who had a female) entered the group. Four members of the RR alliance and a few immature unallied males were in the immediate vicinity and may have participated. Six minutes after the RHP males joined, the KS males split off but continued to follow the RHP and PD males, who remained together. The following day we encountered a resting group of three PD males and eight KS males. The three PD males still had the same female and the group included the four KS members that initiated the conflict the day before.
But another observation in 2006 showed PD and KS teaming up against WC, a second-order alliance:
2006: The fight between 12 KS, three PD and eight WC males was joined in progress. After the fight, the WC males left with a female, and the KS and PD males remained together travelling.
In two interactions between PD and KS, RHP always aligned with PD, allowing PD to prevail both times. But then when WC launched an attack on KS, PD showed up to help KS defeat WC. A theory of dolphin sociality that was based on reciprocity would not predict that KS and PD would work together, given their history of antagonism. Dolphin friendships, then, appear to be more about alliance formation than about reciprocal altruism. What this comes down to is that males tend to team up with other males in a consistent, predictable way, depending on who else is around and not solely based on prior interactions. And this is critical, as these dolphin brawls have important implications for reproductive success. If this sounds complicated, it's because it is. Not only must each dolphin rank the relative importance of his friendships, but he must also be able to predict how the other dolphins rank him.
Sociogram of all dolphin alliances in Shark Bay. Note that PD has a relationship with RHP and KS, though their relationship with RHP is stronger than with KS.
Connor and colleagues note that Only humans and Shark Bay bottlenose dolphins are known to have multiple-level male alliances within a social network. It is unlikely a coincidence that humans and dolphins also have in common the largest brains, relative to body size, among mammals. Our evidence for a third level of alliance formation in the dolphins should refocus attention on the potential cognitive burdens for individuals embedded in such a system, where decisions at one level may have impacts at other levels.
Is there evidence that human friendships have parallels to dolphin friendships? One prevailing theory in social psychology suggests that people choose their friends on the basis of homophily, which is the notion that people associate with others who are similar to them. This is not a new idea: Aristotle wrote that people "love those who are like themselves," and Plato noted that "similarity begets friendship." C.S. Lewis mused, "Friendship is born at that moment when one person says to another: 'What! You, too? Thought I was the only one.'" The other main theory in social psychology predicts that people choose their friends on the basis of propinquity, or geographical closeness.
The social alliances described by Connor et al. are really complicated, requiring big dolphin brains to navigate the subtle social nuances of multi-level dolphin culture. In contrast, the leading social psychological theories of friendship are strikingly simple. Is dolphin society really that much more complex than ours, or are the prevailing theories of human friendship insufficient?
The majority of human friendships occur between individuals who are not related, nor between sexual partners, ruling out kin selection as the underlying mechanism. Reciprocal altruism, as you might expect, is the oft-employed explanation for human friendship formation. In this model, individuals in a friendship each receive benefits in a tit-for-tat, you-scratch-my-back-and-I'll-scratch-yours system of exchange. But social psychologists have found that people do not keep score in close friendships, nor do they resist helping their friends when repayment is unlikely. An evolutionary theory for friendship needs to account for more than just reciprocity.
A new model of human friendship was recently proposed in PLoS ONE, by Peter DeScioli and Robert Kurzban. Participants were asked to list the initials of their ten closest friends (excluding family members and sexual partners), and then to rank them from first to tenth on the basis of closeness. Then, they were asked to divide and distribute one hundred points among each of their ten friends. In the "public" condition, individuals were asked to do so on the assumption that their friends would find out their allocations; in the "private" condition, the allocations would be kept secret.
Allocations in the private condition (left), percent change between private and public conditions (right).
In the private condition, individuals gave the most points to their best friend, the next highest amount of points to the second-best friend, the third highest among of points to the third-best friend, and so on. In the public condition, the allocations were made uniformly. The differential allocation patterns between conditions suggests that humans maintain awareness of the implications of the short- and long-term repercussions of the way they interact with others. And the variable that best predicted how the participants ranked their friends? How they assumed their friends would rank them. That is, Carl woul... Read more »
Connor RC, Watson-Capps JJ, Sherwin WB, & Krützen M. (2010) A new level of complexity in the male alliance networks of Indian Ocean bottlenose dolphins (Tursiops sp.). Biology letters. PMID: 21047850
Many studies of the evolution of music concern the question of what defines music Can birdsong, the song structure of humpback whales, a Thai elephant orchestra, or the interlocking duets of Gibbons be considered music? The answer is of course a simple ‘yes’. A definition of music can easily be stretched to include all types of sound, noises and even plain silence. As such it makes the discussion of what is and what is not music one of the most noticeable pitfalls in the study of music and evolution. An alternative is to separate between the notions of ‘music’ and ‘musicality’, with musicality as a natural, spontaneously developing trait based on and constrained by our cognitive system, and music as a social and cultural construct based on that very musicality. Of course this definition of musicality is still too general to be useful. The challenge is to define what precisely makes up this trait we call musicality. What are the cognitive mechanisms that are essential to perceive, make and appreciate music? Only when we have identified these fundamental mechanisms are we in a position to see how these might have evolved. In other words, the study of the evolution of music cognition is conditional on a characterization of the basic mechanisms that make up musicality.Furthermore, it is important to separate between the biological (or genetic) and cognitive (or functional) aspects that might contribute to musicality. While it is common to assume that there is a mapping between specific genotypes and specific cognitive traits, more and more studies show that genetically distantly related species can show similar cognitive skills; skills that more genetically closely related species fail to show. For example, more and more studies show that humans and certain bird species share their musicality up to a certain level, whereas humans and chimpanzees do not.de Waal, F., & Ferrari, P. (2010). Towards a bottom-up perspective on animal and human cognition Trends in Cognitive Sciences, 14 (5), 201-207 DOI: 10.1016/j.tics.2010.03.003Honing, H., & Ploeger, A. (submitted). Cognition and the evolution of music: pitfalls and prospects. Topics in Cognitive Science (TopiCS)..... Read more »
de Waal, F., & Ferrari, P. (2010) Towards a bottom-up perspective on animal and human cognition. Trends in Cognitive Sciences, 14(5), 201-207. DOI: 10.1016/j.tics.2010.03.003
When you see the lovely images on the cover of a journal, you can be sure that those images are the tip of the iceberg for a cell biologist's “portfolio” of images. Today’s image complements the cover and accompanying paper in this month’s Journal of Biological Chemistry and deserves its own spotlight (yes, I’m referring to HighMag as a “spotlight”). The myosin family of actin motors is large and diverse. One myosin, Myo3A, is found in the stereocilia of the inner ear and has an unconventional structure. Quintero and colleagues recently found that the kinase domain of Myo3a autophosphorylates the motor domain, which alters the localization of Myo3A and decreases the formation of actin protrusions called filopodia in cultured cells. The authors suggest that the function and localization of Myo3A in other bundled actin structures, like stereocilia, are regulated by this auto-inhibition mechanism. Image above shows the actin-binding protein espin (purple) and a mutant form of Myo3A that lacks the kinase domain (white) in a cultured cell. Quintero, O., Moore, J., Unrath, W., Manor, U., Salles, F., Grati, M., Kachar, B., & Yengo, C. (2010). Intermolecular Autophosphorylation Regulates Myosin IIIa Activity and Localization in Parallel Actin Bundles Journal of Biological Chemistry, 285 (46), 35770-35782 DOI: 10.1074/jbc.M110.144360... Read more »
Quintero, O., Moore, J., Unrath, W., Manor, U., Salles, F., Grati, M., Kachar, B., & Yengo, C. (2010) Intermolecular Autophosphorylation Regulates Myosin IIIa Activity and Localization in Parallel Actin Bundles. Journal of Biological Chemistry, 285(46), 35770-35782. DOI: 10.1074/jbc.M110.144360
Which nation is more sustainable: Albania or Angola? Before you place your bet, you might want to consult a new mathematical model that tries to improve efforts to grade countries on how they manage their resources for the long-term.
Although even experts don’t agree on exactly what “sustainability” means, there have been numerous efforts to […] Read More »... Read more »
Phillis, Y., Grigoroudis, E., & Kouikoglou, V. (2010) Sustainability ranking and improvement of countries. Ecological Economics. DOI: 10.1016/j.ecolecon.2010.09.037
For the first time ever, antimatter has been trapped by a magnetic field allowing it to be studied in detail. The 38 atoms were antihydrogen, theoretically the same as hydrogen but having the opposite charge. Where hydrogen is made of one proton, one electron, antihydrogen is made with an antiproton and a positron. Antihydrogen was [...]... Read more »
GPCRs could be a conversation starter over a Thanksgiving Dinner conversation.... Read more »
On the evening of June 5 in 1990, six fishermen prepared a meal of baked fish, boiled rice, boiled potatoes and boiled blue mussels that they had harvested themselves off the coast of Nantucket. An hour after finishing the meal, their mouths started to tingle. Their face, arms, legs and tongue soon went numb. These [...]... Read more »
Murray SA, Mihali TK, & Neilan BA. (2010) Extraordinary conservation, gene loss and positive selection in the evolution of an ancient neurotoxin. Molecular biology and evolution. PMID: 21076133
Now I am not going to try to pretend this entire Nature article. But I read about this as a small article on ScienceNow and decided it might be worth mentioning. Noah Planavsky and his colleagues recently reported in Nature about the evolution of the marine phosphate reservoir, and surmised that phosphate enrichment after the earth . . . → Read More: “Snowball Earth” triggered animal evolution?... Read more »
That is the question, and tentatively answered in the affirmative according to a new paper in The American Journal of Physical Anthropology. A new subclade of mtDNA haplogroup C1 found in icelanders: Evidence of pre-columbian contact?:
Although most mtDNA lineages observed in contemporary Icelanders can be traced to neighboring populations in the British Isles and Scandinavia, [...]... Read more »
Ebenesersdóttir SS, Sigurðsson A, Sánchez-Quinto F, Lalueza-Fox C, Stefánsson K, & Helgason A. (2010) A new subclade of mtDNA haplogroup C1 found in icelanders: Evidence of pre-columbian contact?. American journal of physical anthropology. PMID: 21069749
(with apologies to William Blake). A grain of sand represents many things to a baby turtle. While still within the egg, sand represents a roof over your head, protection from the desiccating sun and from predators, and a blanket to keep you warm and level until its your turn to break free of the nest and do that mad nocturnal dash down the beach to the safety (yeah, right!) of the sea. From the moment of hatching, however, sand presents a range of obstacles to a baby turtle, and believe it or not, the way they overcome those obstacles tells scientists a lot about how things can and should move through and across granular substrates, and maybe offers a few solutions to human problems of this kind too. That’s because, while they look like little clockwork toys ceaselessly flapping their way to some unseen destination, they’re actually engaging in several different types of locomotion, and adapting them on the fly to best suit the substrate they happen to be on. Discovered by Nicole Mazouchova and Nick Gravish from Daniel Goldman’s biomechanics lab at Georgia Tech, these adaptations show us that baby turtles are much cleverer than perhaps we gave them credit for, and they may even explain to some degree why turtles nest on some beaches and not others.
Immediately after hatching a foot or more below the surface of the beach, a baby turtle must get to the surface to draw breath and begin its journey down to the water. That high up a beach, the sand is usually dry and loosely packed. Governed by the laws of physics, sand of this type can act either as a liquid or as a solid, depending on the force applied to it. (if you ever want to see what I mean, add a little water to some corn starch in the palm of your hand until its like whipping cream, and then rub the surface with your other finger. If you rub slowly, your finger will wet, but if you rub fast, the surface will appear dry and your finger will slide right across). To move across this kind of sand, the turtle reaches forward with its front flipper and places it flat on the sand, then digs the leading edge down until the flipper is perpendicular to the surface and mostly buried. By pushing back with just the right amount of force, the sand behind the flipper doesn’t yield, but solidifies like the corn starch in your hand, providing a solid point of leverage against which the turtle can gain traction and push further forward. It then repeats the process on the other side, lurching forward one push at a time with alternating strokes, rather like a rock climber makes progress up a wall. The key thing is that if the turtle pushes too hard or fast, the sand will fluidise and the flipper will pass through it like a liquid, producing no traction; they have to push just the right amount for the physics of the sand to work in their favour. Nick, Nicole and Dr. Goldman observed this in wild loggerhead hatchlings, then showed why this is mathematically, and then created robot turtles that recreated exactly the scenario in the lab to confirm their mathematical model (what, you mean you don’t have a robot turtle hatchling in your lab?). You might think that this kind of motion is pretty inefficient since you effectively stop after each push, but it works well for the hatchlings; they can move three body-lengths per second or more across the sandy surface. That’s the equivalent of a human running at a full sprint, and they’re doing it on dry sand. Good luck matching that effort!
Farther down the beach, the turtle meets a different kind of sand. Wetted and a sorted by the tide, this sand is flat and compacted and the hatchling would be unable to dig its flipper in, so it changes strategy. Instead of digging in and pushing against a block of solidified sand, it jams just the claw on the leading edge of its flipper into the surface like a spike and (with some help from the back flippers) pushes off it, rotating around the point as a pivot, to jam the next point in a little further ahead, just like a skier planting their stocks in the snow as the pivot point for turns.
Farther still, the turtle meets the water. At this critical point, the game changes completely. Instead of moving across a granular surface, the hatchling is now supported by a liquid medium that will never solidify or allow them to gain traction like thy did on the beach. That’s OK, though, because now the turtle gets the benefit of “inertial movement”. That is, it can build up momentum from repeated strokes, unlike on the sand, where as soon as you stop pushing, you stop moving. Movement through this sort of medium requires a totally different motion, so the turtle switches again, this time to the familiar symmetrical flapping that it will use for the rest of its life, creating lift and thrust with every stroke of the paired front flippers.
These biomechanical adaptations to different substrates may have a role to play in why turtles nest on some beaches and not others. That’s because not every sand behaves so predictably. Sands where all the grains are of similar size behave differently from those where the grains vary; and well sorted sands behave differently from poorly sorted sands. You know this is you’ve ever walked on a “squeaky” beach - those sounds come from the friction of sand grains all being the same size (try squeezing a bag of marbles and you’ll see what I mean). Taken together, these adaptations show a remarkable flexibility of locomotion for an animal just in its first hours of life. It must be working well for them, though, because the sea turtle lineage has been doing just fine on this planet for over 200 million years. To borrow from Blake once more:
Every night and every mornSome to misery are born,Every morn and every nightSome are born to sweet delight.
Mazouchova, N., Gravish, N., Savu, A., & Goldman, D. (2010). Utilization of granular solidification during terrestrial locomotion of hatchling sea turtles Biology Letters, 6 (3), 398-401 DOI: 10.1098/rsbl.2009.1041
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Mazouchova, N., Gravish, N., Savu, A., & Goldman, D. (2010) Utilization of granular solidification during terrestrial locomotion of hatchling sea turtles. Biology Letters, 6(3), 398-401. DOI: 10.1098/rsbl.2009.1041
A friend and I were recently taking a stroll down memory lane—remembering elementary school in our respective cities in the Midwest (USA). We were comparing notes on having to read aloud to our classmates—remember that? It was a small group activity, and embarrassing when you came across a word you’d not read or pronounced before. [...]... Read more »
Dehaene S, Pegado F, Braga LW, Ventura P, Filho GN, Jobert A, Dehaene-Lambertz G, Kolinsky R, Morais J, & Cohen L. (2010) How Learning to Read Changes the Cortical Networks for Vision and Language. Science (New York, N.Y.). PMID: 21071632
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