The paper calculates several indices for link importance and site exposure for the Swedish road network, based on the increase in generalized travel cost when links are closed. [ ... ]... Read more »
JENELIUS, E., PETERSEN, T., & MATTSSON, L. (2006) Importance and exposure in road network vulnerability analysis. Transportation Research Part A: Policy and Practice, 40(7), 537-560. DOI: 10.1016/j.tra.2005.11.003
Hammond et al. (2010) challenge the assumption that the more a man aligns himself with (traditional) masculine ideals, the less likely he will be to engage with preventative health services.... Read more »
Hammond, W., Matthews, D., Mohottige, D., Agyemang, A., & Corbie-Smith, G. (2010) Masculinity, Medical Mistrust, and Preventive Health Services Delays Among Community-Dwelling African-American Men. Journal of General Internal Medicine. DOI: 10.1007/s11606-010-1481-z
Think about standing in line to the bus. If everyone cooperates, we get on the bus faster, but some of us may be forced to stand. On the other hand, shoving your way to the beginning of the line will assure you a good seat, albeit at the expense of glares from your fellow-passengers, and maybe a few altercations along the way. In evolutionary terms, selfishness seems like a sounder strategy than cooperating. After all, if you manage to gain a better position for yourself in life’s pecking order, you pass those genes that enable that to your progeny, and further down the line. Why cooperate or act selflessly in the first place? Why let someone else share the gene pool with you when you can have it all to yourself?... Read more »
smith, J., Van Dyken, J., & Zee, P. (2010) A Generalization of Hamilton's Rule for the Evolution of Microbial Cooperation. Science, 328(5986), 1700-1703. DOI: 10.1126/science.1189675
Within the constellation of Ursa Major, about 134 million light years away, an almighty collision is occurring between two galaxies. As the clouds of gas and dust are swirled together an intense burst of star formation is triggered, but is that all that’s been awoken? Has this galactic merger also provided a hidden central black [...]... Read more »
Perez-Torres, Miguel A.; Alberdi, Antxon; Romero-Canizales, Cristina; Bondi, Marco. (2010) Serendipitous discovery of the long-sought AGN in Arp 299-A. Accepted for publication in Letters to Astronomy and Astrophysics. info:/1008.4466
Animal visual systems are evolutionarily tuned to exploit environmental light towards the purposes of spatial perception, navigation, and intraspecific communication. We predominately experience visual information based on variations in the intensity and the wavelengths of incoming light; perceived as brightness and colors. Other animals however, especially the arthropods, also rely on an additional visual modality with which to perceive their world. They are capable of detecting and discriminating different polarizations of light waves.
I've previously discussed how most arthropods detect linearly polarized light (LPL), and last week I summarized the research making mantis shrimp the first animal known to be capable of detecting and discriminating an additional flavor of polarized light, circularly polarized light (CPL). Now, new research has brought a challenger, a jewel scarab beetle (Chrysina gloriosa), into contention for the exclusive CPL sensitivity club. Let's find out how strong the beetle's case is, and weather the mantis shrimp is going to have to share (begrudgingly, I'm sure) the spotlight. ... Read more »
Brady, P., & Cummings, M. (2010) Differential Response to Circularly Polarized Light by the Jewel Scarab Beetle . The American Naturalist, 175(5), 614-620. DOI: 10.1086/651593
Today we’re going to do something a little different. I’ve been posting a lot about reaching movements, because that’s what I’m most interested in, but it may surprise you to learn that humans do actually have the capacity to move other parts of their bodies as well. I know, I’m as shocked as you are… so! The paper I’m going to cover is about the regulation of step variability in walking. It’s a little longer and more complex than normal, so strap yourselves in.Walking is a hard problem, and we’re not really sure how we do it. Like reaching, there are many muscles to coordinate in order to make a step forward. Unlike in arm reaching, these coordinated steps need to follow one another cyclically in such a way as to keep the body stable and upright while simultaneously moving it over terrain that might well be rough and uneven. Just think for a moment about how difficult that is, and what different processes might be involved in the control of such movements.One question that remains unanswered is how we control variability in walking. It’s a simple matter to control average position or velocity, but the variation in these parameters between steps is still unexplained. It is pretty well established that over the long-term people tend to try to minimize energy costs while walking – hence the gait we learn to adopt over the first few years of life. But there’s evidence that such a seemingly “optimal” strategy is not the whole story.Consider walking on a treadmill. What’s the primary goal of continuous treadmill walking? Well, it’s to not fall off. The researchers in the article took that idea and reasoned that because the treadmill is moving at a constant speed, the best way not to fall off is to move at a constant speed yourself. That’s not the only strategy of course – you could also do something a little more complicated like make some short, quick steps followed by some long, slow ones in sequence, which would also keep you on the treadmill.To test how the parameters varied, the researchers used five different walking speeds. You can see this in the figure below (Figure 3 in the paper):Human treadmill walking data with speed as percentage of preferred walking speed (PWS)L is stride length, T is stride time and S is stride speed. So A-C in the figure show how these values change with the five different treadmill speeds – length increases, time decreases and speed increases. D-F show the variability (σ) in these different parameters. G-I show something slightly more complex: a value called α that is defined as a measure of persistence, i.e. how much or little the parameters were corrected on subsequent strides. Values of α > ½ mean that there was less correction, whereas values < ½ mean that there was more correction. So panels G-I show that variability in stride length and time were not generally corrected quickly, but that variations in stride speed were.Read that last paragraph through again to make sure you get it. It will be important shortly!So: now we have a measure of human walking parameters. The question is, how are these parameters produced by the motor control system? That is, what does the system care about when it initiates and monitors walking? Well, one thing we can get from the data here is that the system seems to care about stride speed, but doesn’t care about stride time and stride length individually. And if that’s the case, then as long as the coupled length and time lie on a line that defines the speed, the system should be happy. A line a bit like this (figure 2B in the paper):Human stride parameters lie along line of constant speedThe figure shows the GEM (which stands for Goal Equivalent Manifold, essentially the line of constant speed) plotted against stride time and stride length. The red dots show some data. Right away you can see that the dots generally lie along the line. Ignore the green arrows, but do take note of the blue ones – they’re showing a measure of deviations tangent to (δT) and perpendicular to (δP) the line. Why is δT so much bigger than δP? Because perpendicular variations push you off the line and thus interfere with the goal, whereas tangential variations don’t. So the system is either not stepping off the line much in the first place or correcting heavily when it does.Here’s one more figure (Figure 5C and D in the paper) showing the variability (σ) and persistence (α) for δT and δP :Variability and persistence of deviationsYou can see that δT is much more variable than δP, as you might expect from the shape of the data shown in the second figure. You can also see something else, however: the persistence for δP is less than ½, whereas the persistence for δT is greater than ½. Thus, the system cares very much about correcting not just stride speed but the combination of stride time and stride length that take the stride speed away from the goal speed.Great, you may think, a lot of funny numbers to tell us that the system cares about maintaining a constant speed when it’s trying to maintain a constant speed! What do you scientists get paid for anyway? The cool thing about this paper is that the researchers are trying to figure out precisely how the brain produces these numbers. It turns out that if you just use an ‘optimal’ model that corrects for δP while ignoring δT, you don’t get the same numbers. So that can’t be it. How about if you specify in your model that you have to keep at a certain speed – say the same average speed as in the human data? That doesn’t work either. The numbers are better, but they’re not right.The solution that seems to work best is when the deviations off the GEM line (i.e. δP) are overcorrected for. This controller is sub-optimal, so basically efficiency is being sacrificed for tight control over this parameter. Thus, humans don’t appear to simply minimize energy loss – they also perform more complex corrections depending on the task goal.I’ve covered in a previous post the inkling that this might be the case; while we do tend to minimize energy over the long term, in the short term the optimization process is much more centred around the particular goal, and people are very good at exploiting the inherent variability in the motor system to perform the task more easily. This paper does a great job of testing these hypotheses and providing models to explain how this might happen. What I’d be interested to see in the future is an explanation of why the system is set up to overcorrect like that in the first place – is it overall a more efficient way of producing movement than just a standard optimization over all parameters? Time, perhaps, will tell.---Dingwell JB, John J, & Cusumano JP (2010). Do humans optimally exploit redundancy to control step variability in walking? PLoS computational biology, 6 (7) PMID: 20657664Images copyright © 2010 Dingwell, John & Cusumano... Read more »
Dingwell JB, John J, & Cusumano JP. (2010) Do humans optimally exploit redundancy to control step variability in walking?. PLoS computational biology, 6(7). PMID: 20657664
Over the past decade evolutionary geneticist Mike Lynch has been articulating a model of genome complexity which relies on stochastic factors as the primary motive force by which genome size increases. The argument is articulated in a 2003 paper, and further elaborated in his book The Origins of Genome Architecture. There are several moving parts [...]... Read more »
Whitney KD, & Garland T Jr. (2010) Did Genetic Drift Drive Increases in Genome Complexity?. PLoS Genetics. info:/10.1371/journal.pgen.1001080
A recent paper provides the groundwork to establish a way for exercise to diminish appetite. Or, more likely, for sedentary behavior to increase appetite. Read the rest of this post... | Read the comments on this post...... Read more »
Ropelle, E., Flores, M., Cintra, D., Rocha, G., Pauli, J., Morari, J., de Souza, C., Moraes, J., Prada, P., Guadagnini, D.... (2010) IL-6 and IL-10 Anti-Inflammatory Activity Links Exercise to Hypothalamic Insulin and Leptin Sensitivity through IKKβ and ER Stress Inhibition. PLoS Biology, 8(8). DOI: 10.1371/journal.pbio.1000465
In the last of this series on peace and conflict, we are looking at the question, How can an intractable conflict be resolved or at least transformed into a benign conflict? The attempt here is to use dynamical systems theory or chaos theory to look at the question of intractable conflicts. As mentioned before, an [...]... Read more »
Vallacher, R., Coleman, P., Nowak, A., & Bui-Wrzosinska, L. (2010) Rethinking intractable conflict: The perspective of dynamical systems. American Psychologist, 65(4), 262-278. DOI: 10.1037/a0019290
Figure 1: A mother hyena with her cubs.
Early developmental experiences can have significant implications for the growth, behavior, survival, and reproductive success of an individual. In many species, one of the most important factors that affects an individual's early development is the maternal environment. However, mothers not only provide an environment for their offspring, but also half of their genes, making it difficult to separate the effects of nature and nurture when investigating developmental outcomes in the offspring. Moreover, because male mammals usually disperse from the social groups into which they were born, it is difficult to determine how the maternal environment might influence the reproductive success of sons.
In species with marked sexual dimorphism, such as the red deer (Cervus elaphus), male fitness is related to overall body size and fighting ability. In this case, it is somewhat obvious that a mother of high social status who is able to provide her sons with more resources will result in larger, stronger males. However, in species with less sexual dimorphism, in which male reproductive success is not determined on the basis of body size or fighting ability, it is not clear whether the social status of the mother provides any real benefit to the son, in terms of his future reproductive success. The spotted hyena (Crocuta crocuta) is one such species.
The spotted hyena is a large carnivorous species that lives in "highly structured, female-dominated social groups called clans," in which access to resources is determined on the basis of social status. For that reason, females of high status have higher reproductive value and success than low-status females. In these clans, females generally spend their lives in the group into which they were born, which daughters acquiring a position in the dominance hierarchy close to and below that of their mother. They retain their social status into adulthood, as long as they retain the support of a close female relative. By contrast, male offspring typically leave the clan into which they were born after some time, and immigrate into another clan. However, they do not bring their social status with them. Instead, they must start at the bottom of the social ladder, and as higher-ranking males emigrate to other clans, or die, their social status can increase.
While female reproductive success is ultimately based on the social status of the mother, male reproductive success is dependent on how well the males conform to the preferences of the females. Indeed, females have complete control over who gets to mate with them.
Given the particular features of the social structure of these hyenas, the mechanism by which maternal social status affects the reproductive status of the daughters is quite clear. However, what is less clear is whether the social status of the mother can affect the reproductive status of her sons, especially since his privileged status does not transfer with him to his new clan upon emigration. Previous research of juvenile hyenas raised by adoptive mothers found no evidence of direct maternal genetic effects on the social rank of adopted offspring at adulthood. If a hyena was adopted by a high-ranking mother, he or she retained the high status of the mother irrespective of genetics. Thus, direct genetic effects were ruled out, and the researchers turned to environmental mechanisms.
Using data from a fourteen year study of all members of eight hyena clans resident in the Ngorongoro Crater in Tanzania, a group of researchers from Germany and the UK tested whether maternal social status influenced a number of factors: (1) the growth rate of the suns during infancy and early childhood, (2) their likelihood of immigration into the optimal clan in terms of potential reproductive success, (3) their age at first reproduction, and (4) the duration of residency in the new clan after immigration. They also investigated whether females preferred to mate with sons of high-ranking mothers. Their overall finding was that maternal social status did significantly contribute to the reproductive success of sons. But how?
Read the rest of this post... | Read the comments on this post...... Read more »
Höner, O., Wachter, B., Hofer, H., Wilhelm, K., Thierer, D., Trillmich, F., Burke, T., & East, M. (2010) The fitness of dispersing spotted hyaena sons is influenced by maternal social status. Nature Communications, 1(5), 1-7. DOI: 10.1038/ncomms1059
If you want to know about the life and habitat of a woolly mammoth, there is scarcely a better place to look than in its dung. Found frozen in the permafrost or extracted from the intestines of well-preserved specimens, mammoth coprolites are fecal records of the plants which existed in the animal's local environment and [...]... Read more »
VANGEEL, B., APTROOT, A., BAITTINGER, C., BIRKS, H., BULL, I., CROSS, H., EVERSHED, R., GRAVENDEEL, B., KOMPANJE, E., & KUPERUS, P. (2008) The ecological implications of a Yakutian mammoth's last meal. Quaternary Research, 69(3), 361-376. DOI: 10.1016/j.yqres.2008.02.004
van Geel, B., Guthrie, R., Altmann, J., Broekens, P., Bull, I., Gill, F., Jansen, B., Nieman, A., & Gravendeel, B. (2010) Mycological evidence of coprophagy from the feces of an Alaskan Late Glacial mammoth. Quaternary Science Reviews. DOI: 10.1016/j.quascirev.2010.03.008
This is the fourth in a series of five posts looking at aspects of murder and antisocial behavior. The first post provided an overview of the topic. The second examined relevant epidemiologic research and the third focused on recent genetic research. This post will look at recent brain imaging research.Brain Tutor Screenshot of Orbitofrontal CortexKey brain areas in violent behavior include the frontal lobe and the amygdala. The inferior portion of the frontal lobe is vulnerable to brain trauma. Some victims of traumatic brain injury develop irritability and aggressive behavioral problems. Structural brain imaging has identified several brain volume differences in antisocial personality disorder including:Reduced prefrontal cortex volumesChanges in the right anterior cingulate cortexChanges in the left dorsolateral prefrontal cortexReduction is size (15%) in the right and left amygdalaIncreases in the volume of the striatumThe frontal cortex is key in resisting impulsive behavior and reduced function may modulate the disinhibition found in antisocial personality disorder.Functional brain imaging research is beginning to provide additional information about antisocial personality disorder. A summary of the findings from the functional MRI research literature includes:Reduced amygdala activation to sad or fearful face stimuliDecreased orbital frontal cortex response to emotionally provocative stimuliHyperreactive responses in the mesolimbic dopamine reward systemsReduced task activation in the dorsolateral frontal cortexIncreased task activation in the anterior cingulate and orbitofrontal cortexReduced prefrontal cortex glucose metabolism in PET imagingRight and Left Amygdala in Blue from 3D Brain ScreenshoCrowe and Blair from the NIMH recently published a summary of the functional neuroimaging studies in those with conduct disorder and antisocial personality disorder. They note that aggression can be divided into reactive and instrumental aggression. Reactive aggression involves behavior in response to a threat, while instrumental aggression. Reactive aggression is typically found in children with conduct disorder or oppositional defiant disorder when concurrent mood or anxiety disorders are present. Reactive and instrumental aggression is found in the more classical psychopathic individuals.Crowe and Blair's summary concludes:"FMRI studies have consistently implicated the amygdala and vmPFC (ventromedial prefrontal cortex) in the pathology of individuals with psychopathic tendencies. Dysfunction in this circuitry may relate to the suggestion that the core impairments occurring in this population result from atypical stimulus-reinforcement learning and the representation of outcome information. Such impairments would, in turn, interfere with moral socialization and decision-making." Further brain imaging research holds the promise of increased understanding of violent behavior and the potential for behavioral and pharmacologic interventions. In the next post I will look at the current state of knowledge in the treatment of antisocial behavior.Readers who are interested in the Brain Tutor and 3D Brain iPhone, iPad and iPod Touch application can find a review of these applications in one of my previous posts here.Crowe SL, & Blair RJ (2008). The development of antisocial behavior: what can we learn from functional neuroimaging studies? Development and psychopathology, 20 (4), 1145-59 PMID: 18838035... Read more »
Crowe SL, & Blair RJ. (2008) The development of antisocial behavior: what can we learn from functional neuroimaging studies?. Development and psychopathology, 20(4), 1145-59. PMID: 18838035
As an evolutionary biologist, I’m very familiar with the idea of kin selection. When I saw a paper titled “The evolution of eusociality” in the table of contents of Nature, and read the abstract saying, “Kin selection? Don’t need it,” I thought to myself, “Ooooh, this is big.”
I’ve read blog posts about it on Plektix and Wired. I listened to first author Martin Novak being interviewed on the Nature podcast.
Novak does a good job of explaining why kin selection is invoked to invoke the evolution of sterile castes. I’ll also buy his argument that kin selection needs special conditions to work. But I have yet to read or hear a decent summary for how natural selection can pull off this feat. Novak seems to be saying that mathematically, they are the same.
The Wired article suggests that they are resorting to revived form of group selection. Third author, E.O. Wilson, has certainly been suggesting that group selection should be revived for some time (his co-author on that piece, David Sloan Wilson, is quoted in the Wired article.)
I understand that it can be hard to convey mathematical propositions verbally. But I am currently very unsatisfied with the explanations I’ve heard so far. I may not be along in this.
I am not going to have a chance to read the full paper for a while yet. The first day of our fall semester is Monday, and our library only has a subscription to the print edition of Nature.
So here is a challenge to you, fellow science bloggers! Can anyone explain the gist of this paper and how it shows natural selection explains eusociality – and do it without resorting to equations?
Nowak M, Tarnita C, Wilson E. 2010. The evolution of eusociality Nature 466(7310): 1057-1062. DOI: 10.1038/nature09205... Read more »
Could our growing thirst for biofuels swamp efforts to restore Europe’s wetlands? Not necessarily, finds a complex new analysis of how conservation, energy and farm policies can collide. But exactly how policymakers set the rules may make a big difference to the cost and effectiveness of efforts to protect and expand mires, marshes and bogs. […] Read More »... Read more »
Schleupner, C., & Schneider, U. (2010) Effects of bioenergy policies and targets on European wetland restoration options. Environmental Science . DOI: 10.1016/j.envsci.2010.07.005
The phases of the cell cycle, particularly that of mitosis, were taught in college as part of my studies in biology. The cell cycle is a fundamental process for all organisms and constantly happens within our bodies. While cells generally spend most of the time in interphase, many scientists focus on what happens as the [...]... Read more »
Baker, N., Zeitlin, S., Shi, L., Shah, J., & Berns, M. (2010) Chromosome Tips Damaged in Anaphase Inhibit Cytokinesis. PLoS ONE, 5(8). DOI: 10.1371/journal.pone.0012398
What are the different types of vaccines and how are they made? There are a number of different types of vaccines and each have been developed for different reasons, to prevent different types of disease and to do specific jobs once inside the body. I’ll talk more about the body’s response next week but for now we can just look at the vaccines.... Read more »
Graves PM, Deeks JJ, Demicheli V, & Jefferson T. (2010) Vaccines for preventing cholera: killed whole cell or other subunit vaccines (injected). Cochrane database of systematic reviews (Online). PMID: 20687062
Dhillon S. (2010) DTPa-HBV-IPV/Hib Vaccine (Infanrix hexa): A Review of its Use as Primary and Booster Vaccination. Drugs, 70(8), 1021-58. PMID: 20481658
Once more, we return to those wonderful, phenomenally successful, charismatic beasts.... the toads. As you'll know if you've read the previous articles in the toads series, it seems that most basal divergences within crown-Bufonidae happened in South America. So far as we can tell right now, crown-toads are ancestrally South American, and all of their early history happened on this continent [Rhaebo blombergi image below from here].
All of the basal toads looked at so far - the relatively small, slender-limbed, shallow-snouted members of the clades Melanophrynicus, Atelopus, Osornophryne, Dendrophryniscus, Truebella, Andinophryne, Oreophrynella and Frostius - look rather different from the 'typical' stout-bodied toads that we're more familiar with. Indeed, some authors have suggested that most or all of these 'basal toads' should be grouped together in a toad subfamily termed Atelopinae (recent phylogenetic studies generally agree that no such monophyletic entity exists, however). Having gotten the 'atelopines' out of the way, we now start looking at the more 'typical' toads. As we'll see below (and later), toads in this enormous clade are different in many important respects from 'atelopines' and might be regarded as 'Bufonidae ver 2'. Read the rest of this post... | Read the comments on this post...... Read more »
Van Bocxlaer I, Loader SP, Roelants K, Biju SD, Menegon M, & Bossuyt F. (2010) Gradual adaptation toward a range-expansion phenotype initiated the global radiation of toads. Science (New York, N.Y.), 327(5966), 679-82. PMID: 20133569
Earlier this week, I caught an article in the New York Times covering a rare occurrence: 24 members of a high school football team in Oregon developed rhabdomyolysis (muscle breakdown) from an intense workout with limited water in very hot temperatures. Rhabdomyolysis … Continue reading →... Read more »
Buford TW, Kreider RB, Stout JR, Greenwood M, Campbell B, Spano M, Ziegenfuss T, Lopez H, Landis J, & Antonio J. (2007) International Society of Sports Nutrition position stand: creatine supplementation and exercise. Journal of the International Society of Sports Nutrition, 6. PMID: 17908288
Dalbo VJ, Roberts MD, Stout JR, & Kerksick CM. (2008) Putting to rest the myth of creatine supplementation leading to muscle cramps and dehydration. British journal of sports medicine, 42(7), 567-73. PMID: 18184753
According to some reports, bariatric surgery is now the second most common abdominal surgical procedure performed in the US.
However, despite the well-documented beneficial outcomes, critics continue to question the safety of this treatment option for severe obesity. There is also oft-cited concern about the quality of treatment provided across centres.
These questions were now addressed in [...]... Read more »
Birkmeyer NJ, Dimick JB, Share D, Hawasli A, English WJ, Genaw J, Finks JF, Carlin AM, Birkmeyer JD, & Michigan Bariatric Surgery Collaborative. (2010) Hospital complication rates with bariatric surgery in Michigan. JAMA : the journal of the American Medical Association, 304(4), 435-42. PMID: 20664044
In the absence of GPS, a compass is the best option to find your way around. However, although the earth’s magnetic field is a great way to find your own position, doing the reverse, measuring magnetic fields with a high accuracy — on an atomic scale — remains a challenge. Sure, there are electron microscopes, which are [...]... Read more »
Park, H., Baskin, J., & Zewail, A. (2010) 4D Lorentz Electron Microscopy Imaging: Magnetic Domain Wall Nucleation, Reversal, and Wave Velocity. Nano Letters, 2147483647. DOI: 10.1021/nl102861e
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