Dewlap variation in Anolis distichus in Hispaniola. The photos at the bottom show the change in dewlap color along the two transects in the recent study by Ng and Glor.
Despite all of the research on anole evolution conducted in the last 40 years, one important question still eludes us: how does speciation in anoles occur? This, of course, is of fundamental importance, because the great species richness of these lizards implies that speciation has run rampant in this group. So, we’d like to know why.
We don’t know much about speciation in anoles, but we do know a little. First, it is thought that the dewlap plays an important role. Sympatric anole species almost never have identical dewlaps, and experimental and observational evidence suggests that anoles use their dewlaps for species-recognition. Hence, understanding anole speciation may, to a significant extent, reduce to understanding the factors that cause populations to evolve differences in their dewlaps.
A different perspective on anole speciation relates to the classic question of whether allopatry is necessary or whether, as suggested by many recent studies, natural selection driving differentiation—whether in allopatry or not—is a more important stimulus to genetic differentiation. Recent work in the Lesser Antilles by Thorpe and colleagues has argued that environmental differences are the primary drivers of genetic differentiation within anoles, a result also suggested by Leal and Fleishman’s studies on A. cristatellus in Puerto Rico.
In this light, perhaps the most enigmatic anole is Anolis distichus of Hispaniola.