#evol2010 day 1: In which chromosomes invert and sources sink

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ResearchBlogging.orgThe first day at Evolution 2010 has been a great one. The location in Portland is proving to be great in stereotypical ways: great beer from Rogue Ales, conference t-shirts by American Apparel. There’s pretty good chatter on Twitter this year under the hashtag #evol2010, and in a first for Evolution meeting coverage, there will be daily wrap-up audiocasts (in which I’ll be participating) at the blog Evolution, Development, and Genomics.

Amusingly, we’re sharing the Oregon Convention Center with a “Christian” homeschooling conference, but so far this has led to neither disruptions nor learning experiences.

Some highlights of the talks I’ve attended so far:

  • Jeffrey Feder proposed a new means by which chromosomal inversions might evolve, via a period of allopatric population isolation that allows a locally adaptive inversion to spread, followed by secondary contact during which gene flow creates selective pressure to reduce recombination that could break up the inversion.
  • Simone Des Roches presented new evidence that three lizard species, which have colonized a region of white sand in the New Mexican desert and subsequently evolved “blanched” coloration [PDF], are experiencing ecological release and density compensation. (Simone and her labmate Kayla Hardwick recently discussed their work in blog format.)
  • Chelsea Berns demonstrated that, alone among North American temperate hummingbirds, Ruby-throated hummingbird males have differently-shaped bills from Ruby-throated females.
  • Joel Sachs described the natural frequency and origins of rhizobial bacteria that “cheat” on their host plants.
  • Sheina Sim described host shifts in the apple maggot fly, Rhagoletis pomonella: the fly originally shifted from its native host, hawthorn, to domestic apples [PDF] when they were introduced to North America—now the fly has been introduced to the Pacific Northwest via transport of apples, and some populations have shifted back to hawthorns.
  • The American Society of Naturalists Vice Presidential symposium presented a large volume of work towards discovering the reasons for species’ range boundaries, including great syntheses of population genetic and experimental data for the wildflowers Mimulus cardinalis and Clarkia xantiana—one emerging theme is the importance of the balance of gene flow from healthy populations in the center of ranges to poorly-adapted populations at the edges.

Update, 1950h: The first Evolution 2010 audiocast is now live for download here.

Primary literature referenced

Feder, J., Chilcote, C., & Bush, G. (1988). Genetic differentiation between sympatric host races of the apple maggot fly Rhagoletis pomonella. Nature, 336 (6194), 61-64 DOI: 10.1038/336061a0

Rosenblum, E. (2006). Convergent evolution and divergent selection: lizards at the White Sands ecotone. The American Naturalist, 167 (1), 1-15 DOI: 10.1086/498397

Science online, Portland-bound edition

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Just two days after I get back to Moscow from that Santa Barbara, I’m off again to Portland, for Evolution 2010. As in previous years, I’ll try to post daily notes about cool talks I see at the meeting, and maybe some photos of Portland, where the weather is allegedly going to be warm and sunny. In the meantime, here’s what’s been going on in the science blogosphere this week:

Never again? Photo by Vern and Skeet.
  • Still gushing. Earlier this week, BP removed the containment cap on the Gulf of Mexico oil gusher following a mishap with an underwater robot, but it’s back for now. Internal documents suggest that, early on in the disaster, BP knew a lot more oil was flowing than they told the federal government. Hydrology experts are considering how existing flow control structures might be able to use the Mississippi River itself to protect coastal wetlands from oil.
  • Reconsider that sashimi. An environmentalist group is petitioning to protect bluefin tuna, which spawn in the Gulf of Mexico, under the Endangered Species Act. (NY Times)
  • Meanwhile, in even longer-running fossil fuel disasters. In Pennsylvania coal country, underground mine fires burn unchecked. (SEED Magazine)
  • Walk like a man. A newly-discovered fossil of Australopithecus afarensis—the same species as “Lucy”—has a ribcage more like a human’s than an ape’s, suggesting that it stood upright. (A Primate of Modern Aspect)
  • Why did the moose cross the road? Larger mammals with broader home ranges and lower reproductive rates are at greater risk of becoming roadkill. (Conservation Maven)
  • No word about preference for rock’n’roll, though. Attitudes about sex are better predictors of attitudes about drug use and religion than “abstract political ideologies.” (Blag Hag)
  • Wait, there’s software to do that? You never know when the Methods section of an otherwise obscure paper is going to turn up something useful. (NeuroDojo)

And now, a video of aggregating ladybugs.

How I spent (the first weekend) of my summer not-quite-vacation

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Phylogeny of the Prodoxidae, the family of the yucca moths, with a (very basic) reconstruction of pollinator life habits. Image by jby.

Late last night I made it back to Moscow from (mostly) sunny Santa Barbara, California, where I was lucky enough to attend a summer short course in phylogenetic comparative methods using R, sponsored by NESCent, hosted by NCEAS, and helmed by Luke Harmon and Mike Alfaro. I came into the seminar as a big fan of the programming language R already, and it was great to learn about a whole new range of tools available for the platform. It was even better to learn about those tools in a group of really smart colleagues, all of whom were thinking about how best to use R in their own projects. It was like a warm-up for the Evolution meetings, which start this Friday.

Like the meetings, one of the principal pleasures was learning about everyone else’s study organisms, the best example being the wrinkle-faced bat, which has the strangest trait I think I’ve ever seen in a mammal: a bald face, and a “mask” of furry skin it can pull over said face. Flickr has photos! I’ll put one below the fold in deference to the squeamish.

Eat your heart out, George Lucas. Photo by Evets Lembek.

With conspecifics like these, who needs predators?

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Update, 19 July 2011: More than a year after this study was published, some important objections have been made about very basic assumptions of the experiment presented. Also, I’ve fixed the first link the original article.

ResearchBlogging.orgThere’s something special about islands. After moving to islands, plants adapted to rocky outcrops evolve to grow in rainforests and alpine meadows, and finches evolve to behave like woodpeckers. But why? Islands contain new food sources and habitats, they often lack predators, and they can provide more geographic barriers to generate reproductive isolation—to name just a few possibilities. A newly published ecological experiment now provides evidence that one group of island lizards diversfied because islands are crowded [$a].

There’s something about islands. Photo by Storm Crypt.

Diversification on islands may be related to density compensation, the frequently-observed principle that islands often support fewer species than mainland sites of the same area, but contain more individuals of each species—that is, island populations are usually at higher density than their mainland counterparts [$a]. Density compensation seems to arise both from lack of predators on islands, and because island populations have fewer competitor species. This may mean that, compared to mainland populations, island populations are under weaker natural selection from other species, and stronger selection from competition with other members of their own species.

A somewhat strained analogy

How could that difference in selective regimes spur diversification? Imagine two towns, one surrounded by other settlements, the other on its own in the middle of the wilderness. The town in densely-populated country is probably best off doing one thing well—to have, say, most of its inhabitants working at a factory making (to pick a product at random) sausages for trade with other towns. People living in this first town might want to start up a factory making a different product, but odds are good there’s strong competition from another town nearby, so it’s hard to get the new business off the ground—it’s really just better to invest in the existing factory.

On the other hand, the inhabitants of the town in a lightly-populated district might need more products made locally because it costs too much to import. A businesswoman in the isolated town is probably better off starting a factory that makes a product no-one is making locally—if sausages are already accounted for, there might be a market for (to pick another product at random) pharmeceuticals.

In this scenario, competition from outside exerts economic pressure to do one thing well; competition from within exerts pressure to do many different things. Both kinds of competition are present in each town, but outside competition is stronger in the town surrounded by other towns, and competition from within is stronger in the isolated town.

Anole vs. anole

The density compensation hypothesis proposes that something similar happens on islands. With fewer predators or competitor species, island populations are able to maintain higher densities of individuals. That increased density means that competition within the species becomse stronger, creating natural selection that favors individuals who can use new food resources or live in new habitats.

Density compensation seems likely to be responsible for the diversification of anole lizards on the islands of the Caribbean. In the course of colonizing Caribbean islands, anoles have repeatedly evolved into a handful of different niche specialists [PDF] called “ecomorphs,” ranging from “giant” species that live high in the forest canopy, to small species that can navigate and perch on fine twigs, and intermediate species that live on and around tree trunks. Anoles on the mainland of Central America are no less diverse than their Caribbean congeners, but they haven’t evolved mini-radiations of replicated ecomorphs—and their population densities are much lower than those of the island species.

Anolis sagrei, the brown anole. Photo from WikiMedia Commons.

If release from predators, and the ensuing increase in population density, drove the diversification of island anoles, then we might expect that natural selection from predators has less effect on the traits that differentiate the anole ecomorphs than natural selection from other anoles. Testing that hypothesis experimentally is ambitious to say the least, but that’s what the new study attempts to do.

The authors, Calsbeek and Cox, identified six very small, similar islands off the coast of the Bahamian island Greater Exuma, and introduced varying numbers of brown anoles (Anolis sagrei) onto them at the beginning of the summer. The islands were small enough that Calsbeek and Cox could selectively exclude birds by enclosing the islands in netting; by introducing predatory snakes onto some islands, they could then generate three selective regimes: no predators, birds only, and birds plus snakes. Before introducing them into these experimental setups, the authors measured each anole’s body size, hind-leg length, and running stamina, and marked each lizard so they could estimate selection acting on the three traits based on which lizards survived to be recaptured at the end of the season. (The experiments were carried out over two years, with both years’ results compiled at the end.)

The results suggest that competition makes a bigger difference for the experimental populations than predation—while the strength of natural selection acting on all three traits increased with the anoles’ population density, it didn’t change when predators were allowed access to the islands. If the levels of predation simulated on the micro-islands accurately reflect what anoles experience throughout the Caribbean, then the result is, I’d say, pretty good evidence that competition is the most important evolutionary force acting on island anoles.

I should note that, although Calsbeek and Cox’s raw result is suggestive, it’s not clear that their sample size is big enough to support all the statistical analyses they perform on the data. On balance, I think they deserve a lot of credit just for tackling this question experimentally.

References

Calsbeek, R., & Cox, R. (2010). Experimentally assessing the relative importance of predation and competition as agents of selection. Nature, 465 (7298), 613-6 DOI: 10.1038/nature09020

Givnish, T., Millam, K., Mast, A., Paterson, T., Theim, T., Hipp, A., Henss, J., Smith, J., Wood, K., & Sytsma, K. (2009). Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae). Proceedings of the Royal Society B: Biological Sciences, 276 (1656), 407-16 DOI: 10.1098/rspb.2008.1204

Losos, J. (1990). Ecomorphology, performance capability, and scaling of West Indian Anolis lizards: an evolutionary analysis. Ecological Monographs, 60 (3), 369-88 DOI: 10.2307/1943062

MacArthur, R., Diamond, J., & Karr, J. (1972). Density compensation in island faunas. Ecology, 53 (2) DOI: 10.2307/1934090

Pinto, G., Mahler, D., Harmon, L., & Losos, J. (2008). Testing the island effect in adaptive radiation: rates and patterns of morphological diversification in Caribbean and mainland Anolis lizards. Proceedings of the Royal Society B: Biological Sciences, 275 (1652), 2749-57 DOI: 10.1098/rspb.2008.0686

Science online, southward bound edition

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I’ll take the high road, you take the low road … Photo by gwgs.
  • Still gushing. The Deepwater Horizon well is still not contained. Wednesday BP agreed to set aside $20 billion for an independent reparations fund.
  • Got ’em coming and going. Even if they escape being soaked in oil themselves, seabirds are at considerable risk of eating oil-soaked prey. (Deep Sea News)
  • Me, I just turn left by default. Given a choice between a southern route and a northern route of equal length, people will choose the southern route—apparently because it feels easier. (Wired Science)
  • Who doesn’t want a view of the park? The conservation benefits of protected land can be offset if nearby real estate becomes popular. (Conservation Maven)
  • This is why I’m not a neurologist. Remember all those papers based on fMRI brain scans? Yeah, apparently we’ve only just discovered what fMRI scans actually mean. (Neurotopia)
  • Looking for an open alternative to MatLab? Try Python. (U+003F)
  • What is “forty-two,” Alex? IBM’s next advance in artificial intelligence centers on teaching a supercomputer to answer “Jeopardy” questions. (NY Times)

This week’s video from BBCEarth: David Attenborough says “boo” to a sloth.

Memo to Solid Rock Church, Monroe, Ohio:

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When you rebuild the enormous Jesus-idol that just burned to the ground after being struck by lightening, it probably wouldn’t make it any more sacrilegious if you add a couple of lightening rods.

The graven image, before it experienced the wrath of static electricity. Photo by DRust.

“It sent goosebumps through my whole body because I am a believer,” said Levi Walsh, 29. “Of all the things that could have been struck, I just think that that would be protected. … It’s something that’s not supposed to happen, Jesus burning,” he said. “I had to see it with my own eyes.”

“I can’t believe Jesus was struck,” said his brother, who noted the giant Hustler Hollywood sign for the adult store across the street was untouched. “It’s the last thing I expected to happen.”

Whether jostled by the incident, or ready to call out zingers, all agreed the statue is what makes that stretch of I-75 in front of the church special.

Via Dan Savage, who correctly identifies the violation of the second commandment; and Slacktivist, who implicates Zeus.

And here we have Idaho

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So let’s review how my soon-to-be-Alma Mater, the University of Idaho, has earned national media coverage in the last couple months:

  • U of I scientists discover the allegedly giant Palouse earthworm is actually about eight inches long.
  • This American Life helps a stutter-prone U of I student send a message to the jerks at the local Pizza Pipeline. In a rerun. From 2002.*
The campus water tower. Photo by jby.

———–
* And TAL refers to the student as going to Idaho State, which is located not in Moscow, where the Pizza Pipeline is said to be (and there is one here), but in Pocatello, at the other end of the state. Which is confusing, and additionally vexing given that no one has bothered to correct the discrepancy since 2002.

Not just babble: Cooperating birds talk it through

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ResearchBlogging.orgFor cooperation to work, everyone involved needs to know what the others are willing to contribute in order to decide what she will contribute. You might think that only humans can achieve that kind of back-and-forth negotiation, but a paper recently published online by Proceedings of the Royal Society suggests otherwise. In it, ornithologists decode the negotiations [$a] that allow sociable birds to share the task of watching for predators.

The southern pied babbler, Turdoides bicolor. Photo by Blake Matheson.

Pied babblers (Turdoides bicolor) are sociable South African songbirds, which live and forage for food in groups. During foraging, some adult babblers act as sentinels, perching above the ground to scan for predators, and alerting the rest of the foragers if any danger shows up. Sentinel behavior is cooperative—sentinels free the rest of the group to concentrate on feeding, but sentinels themselves cannot forage. The study’s authors, Bell et al. hypothesized that sentinels might communicate how long they’re willing to stand watch to the rest of the group, so as to prompt new birds to take up watch and given the current sentinels a break to feed.

The authors first established that how hungry a babbler is determines how long he or she is willing to stand watch, which they did by feeding the birds with meal worms immediately after they concluded a period of sentinel duty. Babblers receiving ten worms returned to duty faster than those receiving just one, and stayed on duty longer. Further feeding experiments and observations established that both foragers and sentinels called to each other less frequently when they were well fed, that sentinels called more frequently the longer they stayed on watch, and that sentinels who ultimately stayed on watch the longest also called the least frequently in their first minute on watch.

So call frequency is the babblers’ signal for how badly they want to forage—foragers hearing higher-frequency calls from sentinels should take them as a call for relief; and sentinels hearing lower-frequency calls from foragers should take them as permission to leave the watch and start foraging. To test this hypothesis, the authors played recorded calls to foragers and sentinels, and found that the birds responded as I’ve just described. The apparent babble of the babblers, then, is actually a perpetual negotiation about who should be on sentinel duty—sentinels complaining when they get hungry, and foragers telling the sentinels, “Not yet! I just need to catch a few more worms.”

Reference

Bell, M., Radford, A., Smith, R., Thompson, A., & Ridley, A. (2010). Bargaining babblers: vocal negotiation of cooperative behaviour in a social bird. Proc. Royal Soc. B DOI: 10.1098/rspb.2010.0643

Science online, phylogenetically distant edition

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Louisiana Fish and Wildlife staff rescue an oil-coated pelican. Photo by The News Hour.

As of Thursday night, the Gulf of Mexico oil gusher is capped, but still gushing—and new reports suggest even more oil than previously thought has escaped. Plumes of oil are spreading under the surface of the Gulf. Reports from the American Birding Association are pessimistic at best. On the bright side, an environmental law expert told NPR earlier in the week that criminal prosecution arising from the spill will be “a slam dunk.” Southern Fried Science has compiled the best online sources for oil spill news, including this salty primer on oil containment with booms. I’d add ProPublica’s excellent coverage to the list—and you should go hear ProPublica’s Abrahm Lustgarten tell Terry Gross about BP’s dismal safety record in case you feel your outrage flag.

In non-catastrophic science news:

  • Darwin was right. Again. Confirming a prediction made in The Origin of Species, a recent study shows that bacterial strains are better able to invade cultures of distantly-related strains than closely-related ones. (The EEB & flow)
  • Surprising it’s not higher, really. A survey of marine biology papers suggests that about 25 percent of literature citations are “inappropriate”—but apparently considers citing review articles “inappropriate.” (Neurodojo)
  • Because men are shallow, whatever our orientation. Gay men are 50 percent less likely to be obese than straight men; the reverse is true for women. (Slog)
  • Really, it’s a shame to waste so much neck. Contrary to the current prevailing thinking among paleontologists, at least one sauropod species seems to have used its long neck to reach high-up foliage. (Dinosaur Tracking)
  • Somewhere in here is an episode of Star Trek. Unlike males, female jumping spiders will fight to the death in confrontations over territory—especially if they’re almost ready to lay eggs. (EcoTone, Wired Science)
  • Accidental complexity in the genetic code. Introns, snippets of non-protein-coding DNA interspersed within protein-coding DNA, may have originated as “selfish genes” in our bacterial ancestors. (Wired Science)

This week’s video: BBC footage of aphids’ peculiar lifestyle.

I need to rewatch Starship Troopers

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At the AV Club, Scott Tobias describes in detail how the blockbuster space opera undermines militarism with its own tropes. He also picks up on something I haven’t, embarrassingly enough:

In the scheme of Starship Troopers, it’s important that the actors be pretty and vacuous, and their characters’ romantic dilemmas of the most banal variety imaginable. Hence the casting of Van Dien and Richards in the lead roles, instead of Hollywood stars with more history and substance, who might have torpedoed the film with any hint of self-awareness. (Neil Patrick Harris, as a brainy military intelligence officer who struts around arrogantly in a Gestapo-like trenchcoat, is the only young cast member who seems in on the joke.) … Their shallow conflicts give the film shape and direction, but it’s obvious Verhoeven and Neumeier find them petty and stupid. (One bizarre example: When Van Dien comes to blows with his romantic rival, [director Paul] Verhoeven mutes this grand melodramatic moment by flooding the soundtrack with the dreamy Mazzy Star single “Fade Into You.”)

The propaganda videos interspersed through Troopers are where Verhoeven really tips his hand—they undercut the whiz-bang sci-fi action with moments that should make any thoughtful person squirm. This one uses some imagery that, as Tobias points out, is amazingly prescient for a film made in 1997. (Caution: contains depiction of human-on-alien violence, bitter irony, and Neil Patrick Harris.)