Updated, 2010.06.30: Publish in haste, revise at leisure. I’ve gone back and added some links to original papers mentioned in the talks, and a note on another talk I meant to include (the first in the list, now). And again, 2010.07.02: Added a specific link to the EvoDevoGeno audiocast, and to Vincent Calcagno’s professional page.
The final day of Evolution 2010 featured a fantastic series of talks in the ASN Young Investigators Symposium, and marked the premiere of the iEvoBio sister conference, which ran concurrently today. Perhaps not surprisingly, the #ievobio tag quickly outran the #evol2010 tag on Twitter.
Calcagno, V., Dubosclard, M., & de Mazancourt, C. (2010). Rapid exploiter‐victim coevolution: The race is not always to the swift. The American Naturalist DOI: 10.1086/653665
Duckworth, R., & Kruuk, L. (2009). Evolution of genetic integration between dispersal and colonization ability in a bird. Evolution, 63 (4), 968-77 DOI: 10.1111/j.1558-5646.2009.00625.x
Johnson, M., Smith, S., & Rausher, M. (2009). Plant sex and the evolution of plant defenses against herbivores. Proc. Nat. Acad. Sci. USA, 106 (43), 18079-84 DOI: 10.1073/pnas.0904695106
McGlothlin, J., Jawor, J., & Ketterson, E. (2007). Natural variation in a testosterone‐mediated trade‐off between mating effort and parental effort. The American Naturalist, 170 (6), 864-75 DOI: 10.1086/522838
How do you know it’s getting to be the end of the Evolution 2010 meetings? Because I didn’t get to this until this morning, in the back rows of the SSE symposium on evolutionary prediction. But the third day of the meetings were great, with cool natural history and a great address by SSE president H. Allen Orr.
Ian Pearse presented evidence that introduced oak species were more likely to be attacked by a native herbivore if they were more closely related to native oak species.
Finally, H. Allen Orr capped the day with an SSE presidential address that focused on what we know—and what we don’t—about how reproductive isolation evolves and creates new species. Orr concluded with three conjectures:
Extrinsic postzygotic isolation is usually due to adaptation to ecological conditions,
Intrinsic postzygotic isolation is usually due to adaptation to the intrinsic environment within the genome, and
Prezygotic isolation is usually due to sexual selection.
The idea, of course, is to collect the data to test these conjectures. But I’d say these make pretty good sense based on what we already know.
Edit, 2010.06.30: Swapped the original photo for one that actually depicts a monarch butterfly, as discussed in the comments (thanks, Julie!).
Primary literature referenced
Dudley, S., & File, A. (2007). Kin recognition in an annual plant. Biology Letters, 3 (4), 435-8 DOI: 10.1098/rsbl.2007.0232
In day two, Evolution 2010 is already feeling a mite overwhelming. I started the morning in the SSE symposium on speciation and the origin of dimorphism, then spent the rest of the day bouncing from talk to talk and preparing for my own presentation, which is tomorrow at 9:30. I’m going to bed early tonight, I think.
Luke Harmon presented an impressive but not very conclusive exploration of morphological evolution in squamate reptiles. One insight: once a reptile loses its limbs, its head is free to evolve in new ways, but not always the same ways. Why? Good question.
Primary literature referenced
Bolnick, D. I. & Doebeli, M. (2003). Sexual dimorphism and adaptive speciation: Two sides of the same ecological coin. Evolution 57(11):2433-49 DOI: 10.1111/j.0014-3820.2003.tb01489.x.
Butler, M., & King, A. (2004). Phylogenetic comparative analysis: a modeling approach for adaptive evolution. The American Naturalist, 164 (6), 683-95 DOI: 10.1086/426002
The 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.
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.
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
Just two days after I get back to Moscow from that Santa Barbara, I’m off again to Portland, for Evolution 2010. As in previousyears, 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:
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)
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.
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.
There’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 [$a].
Diversification on islands may be related to density compensation, the frequently-observed principle that islands often support fewer species than mainland sites of the same area, but contain more individuals of each species—that is, island populations are usually at higher density than their mainland counterparts [$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.
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.
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
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.
———– * 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.