Anole Annals

The first poster session at Evolution 2012 got off to a great start last weekend with Rosario Castañeda’s poster on ecomorphological evolution in mainland Anolis.  Currently a post-doc in the Losos Lab at Harvard, where she’s working to bring Anolis to the Encylopedia of Life, Rosario’s Ph.D. thesis with Kevin de Queiroz and associated publication investigated phylogenetics and ecomorphological diversification of the Dactyloa clade of Anolis.  For those who aren’t already familiar with the Dactyloa clade, this group of impressive anoles can be found in the Lesser Antilles and South America.  In her poster, Rosario presents results obtained by combining her multi-locus phylogeny with morphometric data.

Using UPGMA analyses of principal component axes extracted from morphological measurements of 50 species of Dactyloa and 28 species from the Greater Antilles, Rosario initially reported recovering nine distinct morphological clusters (four of which include only one species).  Rosario further reported that these phenotypic clusters do not correspond with monophyletic groups on her phylogenetic tree, suggesting that each cluster did not simply evolve a single time.  Finally, Rosario used distances among species in morphometric space to show that fifteen species in the Dactyloa clade are similar to one of the replicated Greater Antillean anole ecomorphs.  She specifically reported that species from the Dactyloa clade can be assigned to trunk-crown, trunk-ground, and twig ecomorphs.

The Evolution meetings are now ended, but the fond memories linger on. Such as Yoel Stuart reporting the results of his study of character displacement in Mosquito Lagoon, Florida. Dredge spoil islands were created about 50 years ago when the area was dredged, producing big piles of sand which were subsequently colonized by plants and, eventually, green anoles. Within the last 10 years, many islands were invaded by brown anoles, but some remained sagrei free. Yoel set out to compare the green anoles on islands with and without brown anoles.

First, though, he demonstrated the islands with and without brown anoles didn’t differ consistently in any environmental parameter. Thus, nature has set up a very good experiment.

Yoel found that green anoles perch higher in the presence of brown anoles, presumably a result of interspecific interactions. Moreover, on brown anole islands, green anoles have better developed toepads. A common garden experiment reveals that these differences are  not the result of plasticity. Hence, morphological differences have evolved in a very short time as a result of a habitat shift caused by the presence of another species–an excellent example or rapid evolutionary change and character displacement in action.

Many studies find that two populations are extremely genetically differentiated and assume that they are reproductively isolated. Last night, Anthony Geneva reported results of a study that goes the next step, actually testing for the form of reproductive isolation. His focus was on two parapatric members of the Anolis distichus group in Hispaniola that differ in dewlap color and genetically differentiated (see previous talk in this meeting  by Julienne Ng). By bringing individuals into the laboratory and conducting a massive breeding experiment, he tested whether they would mate and produce offspring and, if so, whether the offspring were viable. This is an enormous undertaking–something like this has never been done on anoles.

After one generation of the two generation experiment, some results are already clear. Members of the  interspecific crosses (based on genetic differentiation, they have been named as different species) will mate–no pre-mating isolation, apparently, despite the different dewlap colors; or at least, not complete isolation. However, the number of inviable eggs is greater in the hybrid crosses. No signs yet of Haldane’s rule of any asymmetric degree of postmating isolation, but more work is yet to come.

Recent years have seen great enthusiasm for the idea that populations experiencing different selective pressures will diverge genetically, perhaps to the point of speciation. Ian Wang examined 17 species of Anolis lizards to determine the extent to which genetic differences between populations were a function of ecological differences in the environments they occupy versus geographic differences. Across all 17 species, geography explained twice as much of the variation as did ecological differences, although patterns varied from one species to another. These results suggest that although adaptation to different environment plays some role in driving genetic differentiation, other factors are equally or more important in most cases.