Ecological factors promote convergent evolution and ecological speciation in dwarf chameleons (Bradypodion)

Differing ecological conditions are considered drivers of directional selection among or between populations, resulting in ecological speciation. In particular, divergence of phenotypes in differing habitats, or convergence of phenotypes in similar habitats, can be the result of directional selection. Accordingly, species of dwarf chameleons (Bradypodion) that occur in structurally similar habitats tend to converge on a similar phenotype. Conversely, dwarf chameleons from contrasting habitats have been shown to diverge in phenotype. Thus, ecological speciation appears to be a mechanism for diversification in this genus. Using a combination of morphological (functional and ornamental traits) and population genetic analyses (microsatellite loci), we examined whether three closely related Bradypodion lineages have diverged for these dimensions. We assess whether habitats differ in structure for features related to divergence in morphological traits or whether convergence of traits corresponds to similarity in habitat structure. We find that the three taxa differ significantly at a population genetic level, but some allele sharing suggests incomplete lineage sorting or gene flow. Differences among taxa for functional traits related to gripping of branches (e.g., distal limb size [hands/feet]) can be explained by the perch diameters used by chameleons, whereas the degree of ornamentation differs among taxa in different habitats but is convergent for those in similar habitats. These outcomes are congruent with an ecological model of speciation, with taxa having diverged genetically but showing phenotypic convergence when in similar habitats and divergence when in different habitats.