Category Archives: science

Ecological complexity breeds evolutionary complication

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Photo by futureatlas.

ResearchBlogging.orgCross-posted from Nothing in Biology Makes Sense!

It is a truth universally acknowledged in evolutionary biology, that one species interacting with another species, must be having some effect on that other species’ evolution.

Actually, that’s not really true. Biologists generally agree that predators, prey, parasites, and competitors can exert natural selection on the other species they encounter, but we’re still not sure how much those interactions matter over millions of years of evolutionary history.

On the one hand, groups of species that are engaged in tight coevolutionary relationships are also very diverse, which could mean that coevolution causes diversity. But it could be that the other way around: diversity could create coevolutionary specificity, if larger groups of closely-related species are forced into narower interactions to avoid competing with each other.

Part of the problem is that it’s hard to study a species evolving over time without interacting with any other species—how can we identify the effect of coevolution if we can’t see what happens in its absence? If only we could force some critters to evolve with and without other critters, and compare the results after many generations …

Oh, wait. That is totally possible. And the results have just been published.

A team of evolutionary microbiologists has performed exactly the experiment I outlined above. The study’s lead author is Diane Lawrence, a Ph.D. student in the lab of Timothy Barraclough, who is listed as senior author.

For the experiment, the team isolated five bacterial species, of very different lineages, from pools of water at the bases of beech trees—ephemeral pockets of habitat for all sorts of microbes that break down woody debris, dead leaves, and other detritus. They cultured the bacteria on tea made from beech leaves, in vials containing either a single species, or all five species, and let them evolve for eight weeks—several dozens of bacterial generations. In a particularly clever twist on standard experimental evolution methods, they also used nuclear magnetic resonance (NMR) to identify the carbon compounds in sterilized tea that had been “used up” by the bacterial cultures, and compared the compounds in fresh beech tea to determine what the bacteria were eating.

The base of a beech tree. Photo by -nanio-.

And, maybe not surprisingly, the bacterial species’ evolution with company turned out to be quite a bit from their evolution alone. Left alone, most of the species evolved a faster growth rate. This is a common result in experimental evolution, because the process of transferring evolving bacteria to fresh growth medium—”serial transfers” that were performed fifteen times over the course of the experimetn—can create natural selection that favors fast-growing mutants. But, grown all together in the same tube, species that had evolved faster growth rates in the solo experiment evolved slower growth instead.

To find out what had evolved in the multi-species tubes, the team tested the growth of the bacterial species on beech tea that had been used to grow one of the other species, then sterilized. The original, ancestral strains of bacteria generally had negative effects on each others’ growth—they lived on similar compounds in the beech tea, and so their used tea wasn’t very nourishing for the other species. The same thing occurred with the strains that had evolved alone, only stronger, which makes sense in light of the increased growth rates, which would’ve depleted the growth medium faster.

But the interactions among the strains of the different bacterial species that had evolved together was strikingly different. Many of them actually made the tea more nutritious for other species in the evolved community. That is, some of the bacteria had evolved the capacity to eat the waste products of another species that was evolving with them. Using the NMR method to track changes in the presence of different carbon compounds in the tea before and after use provided confirmation that the co-evolved species were using, and producing, complementary sets of resources.

In short, the evolving community didn’t simply become more diverse—it evolved new kinds of mutually beneficial relationships between species that began as competitors.

Beech leaves—yum? Photo by Colin-47.

That evolutionary shift toward mutual benefit had a significant impact on the bacterial community as a whole, too. Lawrence et al. assembled new communities of bacteria extracted from the end-point of the group evolution experiment, and compared their carbon dioxide production, a proxy for overall metabolic activity, to that of a community assembled from bacteria extracted from the end point of the solo-evolution experiments. The community of co-evolved bacteria produced significantly more carbon dioxide, suggesting they were collectively able to make more use out of the growth medium.

So that’s a pretty nifty set of results, I have to say. But I’m also left wondering what it tells us more generally. In both Lawrence et al.‘s paper, and in accompanying commentary by Martin Tucotte, Michael Corrin, and Marc Johnson, there’s a fair bit of emphasis on the unpredictability of the result. Lawrence et al. write, in their Discussion section,

The way in which species adapted to new conditions in the laboratory when in monoculture—the setting assumed for many evolutionary theories and experiments—provided little information on the outcome of evolution in the diverse community.

And, as Corrin et al. note,

These results imply that predictions constructed from single-species experiments might be of limited use given that most species interact with many others in nature.

So … evolution went differently under different conditions? That isn’t exactly a shocking revelation. The fact that this is one of the study’s major conclusions is a symptom of how little experimental work has actually tested the effects of multiple species on evolution. One experiment I’ve discussed here previously, focused on the joint effects of predators and competitors on microbes that live in pitcher plant pitfalls, similarly emphasized the fact that it wasn’t possible to predict the evolutionary effects of predators and competitors together based solely on their individual effects. Work in this line of inquiry is hanging at the point of establishing that complex conditions lead to complex results.

What I’d really like to know—and I think all the authors of both the paper and the commentary would agree with me on this—is how we can begin to make general predictions about community evolution beyond, “it depends what we put in at the start.” It may be that we’ll need a lot more studies like this current one before we can start to identify common processes, and more interesting trends.◼

References

Turcotte, M., Corrin, M., & Johnson, M. (2012). Adaptive evolution in ecological communities. PLoS Biology, 10 (5) DOI: 10.1371/journal.pbio.1001332

Lawrence, D., Fiegna, F., Behrends, V., Bundy, J., Phillimore, A., Bell, T., & Barraclough, T. (2012). Species interactions alter evolutionary responses to a novel environment. PLoS Biology, 10 (5) DOI: 10.1371/journal.pbio.1001330

Tell the White House: Make government-funded research open-access

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As J.B.S. Haldane put it, “I think … that the public has a right to know what is going on inside the laboratories, for some of which it pays.” He was referring to the need for scientists to explain their work in popular media—which, amen, brother Jack!—but the point holds with regard to access to original scientific articles, too.

It doesn’t make much sense that U.S. citizens, whose taxes fund most of the basic science in this country, are then expected to pay upwards of $50 for a single PDF copy of a journal article presenting government-funded research results. The National Institutes of Health already requires that research it funds be archived online and accessible to the general public free of charge—why not expand that to all government-funded research? And hey, there’s a way to suggest exactly that out to the man in charge: a petition on WhiteHouse.gov.

We believe in the power of the Internet to foster innovation, research, and education. Requiring the published results of taxpayer-funded research to be posted on the Internet in human and machine readable form would provide access to patients and caregivers, students and their teachers, researchers, entrepreneurs, and other taxpayers who paid for the research. Expanding access would speed the research process and increase the return on our investment in scientific research.

The highly successful Public Access Policy of the National Institutes of Health proves that this can be done without disrupting the research process, and we urge President Obama to act now to implement open access policies for all federal agencies that fund scientific research.

It needs 25,000 virtual signatures within 30 days before it’ll get any meaningful attention, so sign this thing and then start badgering all your online “friends” about it, why don’t you? Especially the jerks who keep filling your update stream with branded product promotions and/or time-sucking adorable cat videos and/or news about how they’ve just spent real money for a virtual cow—post this directly on their “walls,” if those are even still a thing, with or without a witty and/or pleading comment appended.

I mean, it’s Monday morning; it’s not like you’re going to get do anything else for the benefit of humanity in the next minute or two, you slacker.◼

Science online, AC/DC edition

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A moonwalk during the Apollo 11 mission. Photo by NASA.

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The living rainbow: “Masculine” is actually “territorial” in electric fish

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ResearchBlogging.orgOne of the most interesting ideas in Joan Roughgarden’s book Evolution’s Rainbow is that across the animal kingdom, many behaviors that we associate with gender—aggressiveness in males, nurturing of young by females—do not line up with biological sex as cleanly as we might think. One good example I’ve discussed before is white-throated sparrows, a species in which either the male or the female in a mated pair can take the aggressive role of defending the pair’s nesting territory.

That principle is echoed in a paper recently published in the journal Behavioral Ecology and Sociology. This time the subject is not birds, but electric fish. Electric fish generate, and can sense, weak electric fields, which they use to navigate their environment—and for social signalling.

Here’s video of a male and female of the species Brachyhypopomus pinnacaudatus interacting, via the website of Philip Stoddard, the senior author on the new study. The fishes’ electric fields are made audible in the soundtrack, as sort of scratchy noises.

Male and female electric fish typically generate detectably different electric signals. However, Stoddard’s team have found some evidence that “masculine” electrical signals may be more generally associated with aggressive social interaction for eletric fish of both sexes—in more crowded conditions, female electric fish start to signal more like males.

The team recorded electric signals from the electric fish Brachyhypopomus gauderio in both a natural population in Guatemala, where population density varied over several sampling periods, and in the lab, under experimentally varied population densities. In both the field and the lab, female fish generated signals with greater amplitude—a “masculine” signal trait—when the population density was higher. Females also generated signals of longer duration—another “masculine” trait—when the ratio of females to males in the population was greater.

Blood tests on female fish in the field study found increased levels of testosterone—which has previously been connected to more “masculine” electrical signals—associated with a higher female-to-male ratio. However, this wasn’t replicated in the lab study.

So it looks like the female fish in this study use the same kind of signalling for aggressive social interaction that males do. That suggests the general differences between male and female signals are more due to differences in how often each sex interacts aggressively than because of physiological differences between the sexes per se.◼

Reference

Gavasa, S., Silva, A., Gonzalez, E., Molina, J., & Stoddard, P. (2012). Social competition masculinizes the communication signals of female electric fish. Behavioral Ecology and Sociobiology DOI: 10.1007/s00265-012-1356-x

The Best Online Science Writing 2012 is now available for pre-order

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For instance, over at Powell’s Books.

This edition includes my long piece on natural selection and human sexual minorities, alongside many other, arguably more worthy, selections from last year’s crop of online science writing, including top-notch work by Crystal D’Kosta, Kate Clancy, Carl Zimmer, Deborah Blum, and Steve Silberman, among many others.

Thanks to Eric M. Johnson, whose great and timely essay “Freedom to Riot” is included in the collection, for the head’s up!◼

Science online, colony collapsing crocodiles edition

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Bees: still not doing well. Photo by net_efekt.

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Nothing in Biology Makes Sense: Making sense of polar bears’ origins

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Polar bear. Photo by ucumari.

This week at the collaborative blog Nothing in Biology Makes Sense, contributor Noah Reid goes in-depth on the recent study pinpointing the historical origins of polar bears, and why it’s taken the most recent systematic methods to correctly pinpoint them.

From 2008 to 2010, a series of algorithms were published that could take data from multiple genes and infer the history of whole populations, a drastic improvement over previous methods that could only identify the history of single genes (e.g. mtDNA). With these methods in mind, a group of researchers gathered data from 14 nuclear genes for multiple extant brown and polar bear populations (Hailer 2012). … the new data analyzed with the new method suggested that polar bears diverged far earlier than previously thought (around 600 thousand years ago) and that they were no longer closely related to the southeast Alaska population, but rather to the common ancestor of all brown bear populations.

For more details, including a nice brief explanation of why it can be important to use multiple genes in reconstructing relationships among species, go read the whole thing.◼

Evolution is undirected, political evolution doubly so

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Pioneering gay rights activist Frank Kameny, at a White House event to commemorate his work. Photo from the White House photo stream.

To everyone wringing their hands over the Obama Administration’s weird collective dance around the question of marriage equality: You do know that evolution is an inherently undirected, frequently random, ultimately goal-less process, right? In which case, the President’s description of his position as “evolving” is an exceptionally apt fit for the inefficient waffling, contradictory signals, and even reversal of previous positions that we’ve observed over the last several years.

See, doesn’t that make you feel better?

Yeah, me neither.

How about this as a kicker instead: evolutionary changes that appear to be directionless over short periods of time may eventually turn out to be part of much longer-term trends.◼

And another thing …

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Regarding that adaptive fairytale about the “runner’s high”—over at Distributed Ecology, Ted Hart points out that it doesn’t make much sense in phylogenetic context, either.

What would be really interesting is to see where this trait maps across the phylogeny. Is it a conserved trait that was selected for in some ancestor? That would point to the fact that maybe it has nothing to do with running. The authors are mute about phylogeny, but eCB’s could alternatively be the ancestral character state, and really the interesting question is why did ferrets evolve the loss of this state? On the other hand maybe the trait evolved multiple times, and that also is really interesting to ask how that happened. But either phylogenetic scenario undermine the central thesis of Raichlen.

You’ll want to read the whole thing, natch.◼

Dr. Pangloss runs a marathon

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Runners in the 2009 New York Marathon. Photo by Whiskeygonebad.

ResearchBlogging.orgThis just came over Twitter (hat tip to @DLiancourt): NPR is running a story claiming that the “runner’s high” some of us feel after a good workout is an adaptation to prompt us to keep fit, or something.

When people exercise aerobically, their bodies can actually make drugs—cannabinoids, the same kind of chemicals in marijuana. [University of Ariona anthropologist David] Raichlen wondered if other distance-running animals also produced those drugs. If so, maybe runner’s high is not some peculiar thing with humans. Maybe it’s an evolutionary payoff for doing something hard and painful, that also helps them survive better, be healthier, hunt better or have more offspring.

So, in a study [$a] pubished in The Journal of Experimental Biology, Raichlen tested this adaptive hypothesis by comparing the levels of these “endogenous cannabinoids” in the blood of humans, dogs, and ferrets after running on a treadmill. The idea being that the ancestors of dogs, like ours, made a living by running—chasing down prey—while ferrets don’t.

So it’s kind of nice to see that Raichlen and his coauthors did, indeed, find that humans and dogs both had higher levels of endogenous cannabinoids in their blood after a run, and the ferrets didn’t. That’s a useful evolutionary data point: it suggests that whatever physiological system prompts endogenous cannabinoid production in connection with exercise dates to (at least) the common ancestor of dogs and humans, and that its preservation in both species may be linked to our shared ability to run long distances.

But it really doesn’t show that this cannabinoid response is an adaptation to reward us for putting in our daily miles.

To really show that the runner’s high is an adaptation, of course, we’d need data that showed (1) observed variation in the runner’s high response has a genetic basis, and (2) people who had get stronger runner’s highs have more babies. But even apart from that, the understanding of what is good for us today—getting off our butts and going for a run—isn’t particularly that well connencted to the lives of our proto-human ancestors. Does Raichlen really think that early humans (or dogs, or any other animal that chases down prey) would just sit around and go hungry if we didn’t have a cannabinoid payoff at the end of the hunt?

And then, in the text of the very same NPR article, an orthopedic surgeon is quoted saying that the “runner’s high” can actually be a problem:

[Dr. Christina] Morganti treats runners for injuries and she says they’re the worst patients. “The treatment is to stop running,” she says. “They won’t. They don’t want to. A lot of the behavior is not unlike the patients we have who are seeking drugs. It’s really similar. It’s an addiction.”

So … a physiological response that prompts some of us to run even when running is likely to exacerbate injury is a good thing? How, exactly, would giving yourself shin splints lead to greater reproductive fitness if you’re making a living hunting gazelles on the savannah? I’m going to go out on a limb and say it wouldn’t.

Here’s an alternative hypothesis, which I freely admit is no better supported by the available data: the endogenous cannabinoid response isn’t a “reward” for running. Instead, it helped our ancestors tolerate the stress of running when they needed to, by letting them ignore minor pains and press on after that one elusive, tasty antelope. For our ancestors, dinner was the reward for running, not the cannabinoids. In the modern world, where we don’t run for our dinners, we’ve re-purposed the pleasant persistance of those cannabinoids as a motivation to replace that original life-or-death need.

Whatever the actual evolutionary origins of the “runner’s high,” the idea that it’s an adaptive reward for exercise is nothing more than adaptive storytelling filtered through the lens of our modern, very unnatural, lives. Don’t get me wrong—I love to run, and in fact I’m a month away from my fourth marathon. But I’m not going to pretend that I’ll be running those 26.2 miles because natural selection wants me to.◼

Reference

Raichlen, D., Foster, A., Gerdeman, G., Seillier, A., & Giuffrida, A. (2012). Wired to run: exercise-induced endocannabinoid signaling in humans and cursorial mammals with implications for the ‘runner’s high’ Journal of Experimental Biology, 215 (8), 1331-6 DOI: 10.1242/jeb.063677