Category Archives: science

Released from predators, guppies reshape themselves—and their environment

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A (domestic) male guppy. Photo by gartenfreuden.

ResearchBlogging.orgConsider a population of guppies living in the Aripo River in Trinidad. They have a happy existence, as far as guppies can be happy, but their lives are shaped by the constant threat of larger, predatory fish. The river runs clear over a colorful gravel bed, and guppies who stand out against that background are eaten quickly. Even guppies whose coloration helps them blend in have to be ready to make a break for it if a predator shows up. All in all, a guppy’s chances of surviving to mate depends most on its ability to hide from bigger fish, and to swim quickly when it can’t hide.

Then one fine day a biologist comes along, scoops up a couple hundred guppies, and moves them to a pool in a tributary of the river. The pool is separated from the mainstream by a series of waterfalls, so larger fish can’t swim up—the guppies are now free from their most dangerous predators. They can be fruitful and multiply. In this new habitat, camouflage and evasive maneuvers don’t matter so much. What does matter is finding enough food to make some babies in the midst of a whole bunch of other guppies who are also not particularly worried about predators.

John Endler started the experiment I’ve just described back in 1976 to see whether guppies’ coloration helps them hide from predators [PDF]. The guppies he moved to a predator-free stream have continued to evolve, though, and three decades later, new studies are showing how release from predators changed the guppies—and how those changed guppies could be changing the living community around them.

Since the 1976 introduction, Endler and other biologists have tracked the Aripo River guppies’ response to the change in natural selection he created. Release from predators is considered one of the classic sources of ecological opportunity that can free a population to evolve new traits and behaviors, and explore new ways of making a living. At the same time, a sudden lack of predators means that competition within the population can become stronger.

Points of measurement for guppy body and head shape, illustrated on a stained specimen. Image from Palkovacs et al, fig. 1.

In one study just published by PLoS ONE, Eric Palkovacs and two colleagues compared the body shape of guppies from the experimental population with guppies from the source stream. (Endler had noted changes in body shape along with changes in coloration in his original paper.) First, Palkovacs and his coauthors gauged how rapidly female guppies taken from each site snapped up standardized food. Then they killed the test fish, treated them with stain, and measured their body and head shape. Fish from the site with lower predation ate faster, and they had bigger mouths and deeper bodies than fish from the site with more predators.

Palkovacs and his coauthors also observed that the guppy populations at the experimental site were denser—without predators thinning them out, the fish are probably most limited by their food supply. A study published last year in PNAS suggests that this denser guppy population might reshape its own environment. The paper’s authors created artificial ponds stocked with algae and small invertebrates, then introduced guppies from the high-predation source site or from the low-predation experimental site. They also controlled for the differences in guppy population density associated with predator pressure, maintaining the fish at either the high density observed with low predation, or the lower density observed with high predation.

Where the guppies came from made a significant difference in the artificial ecosystems, and these differences were in some cases exaggerated by the increased population density caused by predator release. Guppies from the “released” site ate less selectively than guppies from the site experiencing higher predation, who favored invertebrates over algae. As a result, guppies from the released site were associated with less algae growth, and higher invertebrate population density. Probably because they ate more plant matter, guppies from the released site also excreted less nitrogen, reducing the nutrient’s availability for plant growth.

These results echo a study I discussed last year, which used a very similar approach to show that speciating sticklebacks can change their environment. It’s another reminder that evolutionary change can feed back to change the environmental conditions that prompted change in the first place—that natural selection operates in the midst of continuous change.

References

Bassar, R., Marshall, M., Lopez-Sepulcre, A., Zandona, E., Auer, S., Travis, J., Pringle, C., Flecker, A., Thomas, S., Fraser, D., & Reznick, D. (2010). Local adaptation in Trinidadian guppies alters ecosystem processes. Proc. Nat. Acad. Sciences USA, 107 (8), 3616-21 DOI: 10.1073/pnas.0908023107

Endler, J. (1980). Natural selection on color patterns in Poecilia reticulata. Evolution, 34 (1), 76-91 DOI: 10.2307/2408316

Palkovacs, E., Wasserman, B., & Kinnison, M. (2011). Eco-evolutionary trophic dynamics: Loss of top predators drives trophic evolution and ecology of prey. PLoS ONE, 6 (4) DOI: 10.1371/journal.pone.0018879

Tipping your online science writers

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Tip jar. Photo by burningkarma.

I woke up this morning to learn that Ed Yong liked my post about quasi-carnivorous plants so much that he’s willing to pay for it. That is, Ed’s included my post in his monthly collection of online science writing worthy of a sort of collective tip jar—he pledges £3 to each of the selected authors, and collects donations from his readers to divvy up amongst the authors at the end of the month. It’s a cool initiative that’s been underway for a couple months, so it’s a mite embarrassing that I’m only mentioning it now that I’ve been included.

In any event, I’m pretty sure this marks the first time I’ve been paid for a piece of writing—certainly the first time I’ve been paid for a post to Denim and Tweed—and I’m honored to be included in a list alongside top-notch science writers like Brian Switek, Jonah Lehrer, and Maryn Mckenna. I strongly encourage you to read them all, and consider putting something in the tip jar.

Carnival of Evolution, May 2011

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Carnival. Photo by Mastery of Maps.

What has two thumbs and forgot to submit to the Carnival of Evolution this month? This guy. But not to fear—lots of other great science writers remembered the deadline, and the new edition of the blog carnival collecting online writing about evolution and its implications is now online at Lab Rat’s blog. Go check it out!

Science online, harm-reducing space squid edition

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It’s not easy being green. Photo by Twin Peaks.

Today’s save the frogs day—donate, cut your pesticide use, build a backyard pond, or maybe help an amorous amphibian cross the road.

  • Two (thousand) drifters, off to see the world/ there’s such a lot of world to see … Fire ants cross bodies of water by forming themselves into a raft.
  • Worse than fashion mags. Seriously. Want to give your teenager body image issues? Subscribe to a fitness magazine.
  • Orchids will do anything for pollination. An orchid’s brown-spotted leaves and rotten odor convince flies that the flower is dying from a fungal infection, so they’ll pick up pollen while trying to feed on the fake decay.
  • Babies are smarter than we thought. A classical developmental psychology test turns out not to document a bug in the way human infants think about the world, but a feature of social learning.
  • Harm reduced. The city of Vancouver has dramatically reduced overdose death rates by opening Insite, a facility that allows addicts to use drugs under medical supervision.
  • Cephalopod: A Space Odyssey. NASA will send squids into space on the final flight of the shuttle Endeavour.
  • Introspection with your natural history. Brian Switek muses on the future of science writing.

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The road ahead

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Minneapolis, one of my two new hometowns. Photo by jby.

So, now that I’ve defended my dissertation, there’s really not much of grad school left for me. I have to turn in a final, committee-approved version of the dissertation text, and then on May 14 I’ll put on some Hogwarts-worthy getup and accept my diploma from the University of Idaho. I also have some final grading to deal with (Whose bright idea was it to add an independent reading report to the lab curriculum? Oh, right. Mine.) and I’d like very much to get my last Joshua tree paper ready for submission. But, after all that—what’s next?

As it happens, I’ve known that for some time, but there didn’t seem to be a good opportunity to cover it here before now: I’m going to Minnesota.

Specifically, I’ll be starting a post-doctoral position with Peter Tiffin’s lab at the University of Minnesota, Saint Paul. I’m going to be joining a project studying the population genetics of the interaction between plants and nitrogen-fixing bacteria, using the legume Medicago truncatula as an experimental model. It’s a big, multi-lab, multi-institution collaboration, working with genomic data for both Medicago and the bacteria it hosts, Sinorhizobia.

My new favorite plant, Medicago truncatula. Photo by Minette Layne.

So I’ll be studying a mutualism that might work a bit like yucca pollination—but then again, it might not. The plant-rhizobium interaction is much more widespread than obligate pollination mutualism, and has probably played a big role in the diversification of land plants. Plus, I’ll be working with genome-scale data—it’s all on a totally different scale from anything I’ve done before. There are possibilities for experiments and analyses that we’ll never be able to do with Joshua trees—ye gads, greenhouse experiments!—and it’ll be a learning experience at every step. And, equally importantly, my new collaborators at the Tiffin lab and the other research groups involved in the Medicago genome project are a smart, friendly bunch—I’m looking forward to working with them. All in all, it’s exactly what I want in a postdoc.

Saint Paul and Minneapolis look like a pretty nice place to spend the next couple years, too. It’s not just that they’re cities after six years in small-town Idaho—they’ve got solid mass transit and they’re ranked alongside Portland, Oregon for bicycle-friendliness. One of my new senators will be Al Franken. The Twin Cities are the home turf for Public Radio powerhouse American Public Media. Minneapolis was even named the gayest city in America by the Advocate, and I don’t think that was meant as some sort of elaborate joke.

It’s hard to complain about the new neighbors, either: My new U of M colleagues will include George Weiblen, an expert on the other classic obligate pollination mutualism; G. David Tilman, who’s done pioneering work on the ways competition and other species interactions structure natural communities; and Ruth Shaw, who helped lay the foundation for the ways we measure natural selection today. On the science blogging front, none other than P.Z. Myers will be another U of M colleague (at the Morris campus), and BoingBoing’s science guru Maggie Koerth-Baker is in town.

Of course, as I’ve learned from years of Garrison Keillor exposure, winter in Minnesota does not mess around. Fortunately I’m moving immediately after graduation in mid-May, so I’ll have some time to brace myself. Apartment-hunting priorities include covered parking.

All of this is a long and digressive way of saying, yet again, that I’m making some pretty major changes in the next few weeks. Expect further irregularities in posting, and maybe even a radical reconsideration of how D&T fits in my schedule—I don’t yet know what my life will look like once I’ve settled into postdoc-hood, though I’m excited to find out.

Deprived of pollinators, flowers evolve to do without

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Who needs pollinators? Not monkeyflowers—at least not after a few generations of evolution. Photo by Brewbooks.

ResearchBlogging.orgThe loss of animal pollinators poses a potentially big problem for plants. However, many plant species that rely on animals to move pollen from anther to stigma have the capacity to make due if that service goes undone—and, as a new study released online early by the journal Evolution demonstrates, such plants can rapidly evolve to do without pollinators [$a] if they must.

The paper’s authors, Sarah Bodbyl Roels and John Kelly, demonstrate this using a simple greenhouse experiment with the monkeyflower Mimulus guttatus, a wildflower native to western North America, and a member of a genus rapidly developing into a major model system for studying the evolution of ecological isolation and floral evolution.

Mimulus species vary in their reliance on animal pollinators—some grow minimalistic flowers, with the anther so close to the stigma that pollen transfers without any assistance. In natural populations, M. guttatus is usually pollinated by bees, but individual plants vary in the distance between anther and stigma, and this variation has a genetic basis. So a population of M. guttatus deprived of pollinators would have the raw material to evolve a solution—natural selection would favor plants that are better able to self-pollinate. As the population evolved to be more self-fertilizing, it might also evolve to look more like self-pollinating Mimulus species, losing the bright petals that attract pollinators.

To see whether this could actually happen, Bobdyl Roels and Kelly challenged an experimental population of Mimulus guttatus to do without pollinators, and tracked its response.

The authors raised seeds derived from a natural wild population of Mimulus guttatus in greenhouses under two trial conditions: control populations were provided with hives of bumblebees to pollinate them when their flowers were ready for servicing; and experimental populations were left to produce what seed they could without pollinators. The authors collected the seeds produced by each population, and planted them to form the next generation.

A bumblebee digs for nectar in flowers of Mimulus moschatus. Photo by Mollivan Jon.

Early on in the experiment, the experimental populations deprived of pollinators fared badly. Without pollinators, the average plant produced two seeds or fewer by the end of the generation, compared to eight or ten seeds per plant in the population provided with bees. By the fifth generation, however, this was starting to improve—plants in both populations without pollinators were producing more seeds, and one of the two experimental populations produced nearly as many seeds as the control plants.

Examining the traits of plants produced by this final generation (actually, the grand-offspring of the fifth generation, to control for effects of inbreeding), the authors found that the average distance between the pollen-producing anther and the pollen-receiving stigma had shrunk significantly in plants from the experimental population. Across all the treatments, plants with a shorter distance between stigma and anther produced more self-pollinated seeds. There was no evolved change in other floral measurements, however—plants in the no-pollinators treatment had petals as big and showy as plants evolved with bumble bees.

In a natural population of Mimulus guttatus, the drop-off in seed production created by loss of pollinators should have much the same effect as in this experiment, creating a strong selective advantage for individual plants that can make more seeds on their own. The fact that the experimental plants did not evolve reduced petals could mean that in the cushy conditions of a greenhouse, there wasn’t much need to stop spending resources making showy flowers. Or maybe, when the major source of natural selection is the need to make any seeds at all, selection to save resources on flower production is relatively weak and correspondingly slow-acting.

As the authors point out, one of many changes humans are making to natural communities around the world is to disrupt pollination relationships. In a sense, experiments like theirs are being carried out worldwide, on hundreds of plant species—and each species will adapt, or fail to adapt, in its own way.

Reference

Bodbyl Roels, S., & Kelly, J. (2011). Rapid evolution caused by pollinator loss in Mimulus guttatus. Evolution DOI: 10.1111/j.1558-5646.2011.01326.x

Science online, back online edition

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Suck it, tigers. Photo by Billtacular.

I didn’t do a linkfest last week, what with having other things on my mind, so this list may be longer than average. You should read them all.

  • Converging … on poison! Both bird’s foot trefoil and the burnet moth caterpillars that eat it have independently evolved the ability to synthesize two cyanide-based toxins.
  • Not what you want to read the week you defend your Ph.D. A guy who anticipated two previous economic bubbles thinks that the next one to burst could be higher education.
  • Born free, but do they want to stay free? Whether animals are happier in the wild depends on what kind of life they could have in captivity.
  • Better offense and better defense. How “natural” resistance to HIV infection works, on a cellular level.
  • “Third gender” ≠ “gay.” The many ways modern cultures grapple with human sexual diversity shed light on the “gay” non-caveman.
  • Also less cute, in my opinion. When you consider their respective ecological roles, tigers are less important than warblers.
  • Unhappy anniversary. A year after the Gulf of Mexico oil spill, we still don’t know what effects the oil and chemical dispersants may have on sea life—but there are plenty of reasons to worry.
  • Your wardrobe, under the microscope. Anthropological consideration of why women (and men) wear high heels, as well as why those heels might be black.
  • Shakespeare, evolution, and Kubrick’s Space Odyssey: brilliant. Brutish, aggressive chimpanzees have long been the assumed model for earlier humans—but more peaceful bonobos might be closer to the truth.
  • Might as well give up on drug development right now. Masturbation (or, rather, orgasm) has been found to relieve restless leg syndrome.

And there was much rejoicing

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As already noted in other venues, yesterday I passed my dissertation defense. There has been what I’d call an appropriate amount of celebration (as a result of which I’m taking it slow today) and I’ve been overwhelmed by congratulations in multiple media—thanks, everyone!

What’s in that dissertation, anyway?

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About to take the plunge. Photo by jby.

So, what with getting my sparrows in a row for my dissertation defense on Friday, I haven’t written any new science post for this week. But! As it happens, I have written about most of the component chapters of my dissertation—so in lieu of something new this week, why not check out those posts?

  • The first chapter of my dissertation is a literature review about the phenomenon ecologists call ecological opportunity, and how it may or may not explain big, rapid evolutionary changes. I’ve also written about this topic for the Scientific American guest blog.
  • The second chapter uses phylogenetic methods to reconstruct what yucca moths were like before they were yucca moths.
  • The third chapter presents a mathematical model of coevolution between two species, and determines what kind of interactions—predation, parasitism, mutualism, competition—can cause those species to evolve greater diversity.
  • The fourth chapter is the latest work on my lab’s big study of Joshua trees and their pollinators. The material I’m including in this chapter hasn’t been reviewed and published yet, but you can read the most recent Joshua tree post to learn what we know so far, and what kinds of questions we still want to answer.

Regular posting resumes next week, provided that I pass my defense and the celebrating afterward doesn’t interfere with my blogging capacity.

Science online, bracing for impact edition

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Ho-hum. Photo by v1ctory_1s_m1ne.

A week from today, I defend my dissertation. Fortunately, Eric Michael Johnson pointed out to me that the most worrisome possible question has been answered. So I’m all set!