Joel McGlothlin received the 2011 Dobzhansky Prize, given to an outstanding young scientist in the field of evolutionary biology. Successfully fending off technical AV difficulties, Joel gave a fascinating talk in which he examined the idea that evolution should occur along lines of least genetic resistance, which are determined by the genetic correlations among traits. This hypothesis predicts that as traits diverge, they should diverge in ways that mirror the trait genetic correlations. Moreover, one would expect that this effect would attenuate over time, so that more distantly related species would show less evidence of diverging along these lines.
Author: Jonathan Losos Page 119 of 130
Professor of Biology and Director of the Living Earth Collaborative at Washington University in Saint Louis. I've spent my entire professional career studying anoles and have discovered that the more I learn about anoles, the more I realize I don't know.
Luke Mahler received this year’s Fisher Award, given by the Society for the Study of Evolution for the best paper emanating from a Ph.D. thesis published in Evolution in the preceding year. Mahler asked “what is the trigger for adaptive radiation?” and answered, “ecological opportunity”: a wealth of evolutionarily accessible resources (from Schluter). This leads to the prediction that the pace of adaptive radiation is regulated by competition, and is thus diversity-dependent. This hypothesis has been tested greatly in recent years by seeing if the rate of species diversification decreases through time as a clade radiates. But, Mahler argued, counting species is not enough—rather, we need to focus on patterns of diversification in adaptive traits.
Focusing on Greater Antillean anoles, Mahler asked whether rates of ecomorphological diversification decline as the number of species on an island increases. Testing this hypothesis requires estimating historical ecological opportunity (EO) by inferring ancestral species richness on an island and estimating rates of morphological evolution at ancestral nodes and how they changed as a function EO. To do this, Mahler and co-author Liam Revell developed at maximum likelihood approach to infer ancestral states incorporating uncertainty on the reconstruction of ancestral biogeographic locations.
The result is strong support for the ecological opportunity model. Rates of ecomorphological evolution are high early in anole radiation, but decline with increasing species richness.
Anolis sagrei from near one of Dan Warner's field sites. Photo by Aaron Reedy.
American Society of Naturalists’ Young Investigator Award winner Dan Warner presented a marvelous synthesis of studies of how external influences affect phenotype and survival in eggs and offspring of lizards and turtles. Among other things, he has demonstrated
that some types of plasticity are adaptive: in temperature sensitive sex determining lizards, males are produced at temperatures at which the fitness of male offspring is greater than that of females, and vice-versa.
In a fascinating talk, Chad Watkins reported the discovery of a surprising frequency of homeotic mutations along the anterior-posterior axis and implicated the high rate of transposons in the Hox D cluster as a possible cause. Watkins reported that 27% of DNA in the HoxD cluster is comprised of transposons, much higher than in other vertebrates. Moreover, Hox D gene expression is shifted posteriorly. For example, Hox D10 normally should express at anterior boundary of hip, but in A. carolinensis it is all the way down at the tip of the tail. Further, in later stage embryo, ectopic expression of D13 occurs in the hand and feet, which is novel in vertebrates. Could this be related to ecomorph differentiation in limb elements?
Yoel Stuart reported on studies of sympatric anoles on small, man-made islands in Mosquito Lagoon in the Intra-Coastal Waterway in Florida. These dredge spoil islands were naturally colonized by A. carolinensis and more recently—sometimes by the hand of man—by A. sagrei. Surveying a dozen or so islands, Yoel asked whether the green anoles differ in the habitat use and morphology depending on whether they occur with brown anoles. Because we know that brown anoles are recent arrivals, any differences would be recent in origin.
Sure enough, in the presence of browns, green anoles perch higher and have larger toepads. Assuming that the change is genetic, the rate of change would be among the fastest ever recorded. But that’s a big assumption, and as Yoel notes, laboratory studies are needed to investigate whether differences truly are genetically based. Given that the number of lamellae is a trait thought to be fixed at birth, environmentally driven phenotypic plasticity seems unlikely, but this needs to be examined directly. In addition, Yoel plans to measure vegetation structure on the islands to investigate whether, by chance, differences exist between islands with and without brown anoles.
Although the A. carolinensis genome is not yet published, it is already being widely used in comparative genomic studies. In a very interesting talk, Matt Fujita reported on the GC content of the anole genome in comparison to other taxa, with special focus on bird and mammal genomes. It turns out that the anole genome differs in many interesting respects. One particular focus was on isochores, which are long stretches of the genome with high GC content. It turns out that the anole genome contains a substantially lower proportion of isochores, and that the distribution of GC content is much more homogeneous across the genome.
In an impressive synthesis of previous (Cox and Calsbeek, 2010; Cox et al., 2011)
and new work, Bob Cox reported on studies examining the adaptive significance
of sex ratio variation in brown anoles. Previous lab studies had indicated that
when a female brown anole mates with a large male, she tends to produce sons,
whereas when she mates with a smaller male, she disproportionately produces
daughters. Cox and colleagues set out to test why that might be so by producing
offspring with known parents in the lab, and then releasing them into the wild. The idea was to test whether sons fathered by larger males survived better than sons produced by small males and, conversely, whether daughters from small males fared better. They tested a number of other hypotheses, namely that females in good condition produced males which survived better (the Trivers-Willard hypothesis); that condition of males should affect survival of offspring; and that early hatching lizards survived better (a hypothesis suggested by early iterations of the experiment).
The hypotheses were evaluated in two stages: whether offspring production was a function of parent phenotype, and whether offspring survival was related to parent phenotype.
The most strongly supported hypothesis was the initial one: female ability to link offspring sex with paternal phenotype appears adaptive; male offspring fathered by large males and females sired by small males have highest fitness. Other hypotheses were less variably supported: either the sex of the offspring was not related to the condition of the parent, or no survival advantage was found.
The meetings kick off tonight in stinkin’ hot Norman, Ok. From the program guide, here are the anole-themed talks. Can’t attend? Fear not–AA will keep you abreast of events as they unfold.
Sunday, 2:45 P.M. University A, Cox, Robert, Urbach, Davnah, Duryea, M.C., Calsbeek, Ryan. Testing the adaptive significance of progeny sex-ratio bias in the brown anole lizard, Anolis sagrei.
Lizard in an Evolutionary Tree's reworking of Williams' classic figure. Note that A. gundlachi is a trunk-ground anole, not, as indicated, a trunk-crown anole.
In this famous figure, Ernest Williams sketched out his view of how anole diversification occurred on the Greater Antilles, using Puerto Rico as an example. First, species diverge to use different structural habitat, producing the different ecomorphs. Subsequently, within-ecomorph divergence produces species that use the same structural habitat, but which occupy different climatic micro-climates, ranging from cool and moist rainforest to blazing hot and dry semi-desert. This two-stage pattern of evolution is displayed not only on Puerto Rico, but also on Cuba and Hispaniola (Jamaica, the most species deprived island, has little within ecomorph diversity).
In contrast to the plenitude of research in recent years on the adaptive basis of morphological differences among the ecomorphs, relatively little work has focused on the extent to which closely related species—members of the same ecomorph class—have adapted to occupying different microclimates.
Andrea Barragán Forero [andreabarragan10@hotmail.com] is working with A. concolor and A. pinchoti from the collection of the National University of Colombia. She is investigating whether the species are sexually dimorphic in size and shape, and if their morphology is similar to the Greater Antillean ecomorphs. Her work is entitled: Diversificación morfológica de Anolis solitarios: Anolis concolor y Anolis pinchoti de las islas de San Andrés, Providencia y Santa Catalina, Colombia.
Andrea could really use a photograph of a live A. pinchoti. If you can help her, please email her.