The Evolution of Ecomorphological Convergence in Dwarf Chameleons (Bradypodion)

Environmental variation can drive patterns of directional selection, often leading to adaptive changes in shape and form. When selection pressures are strong, different lineages may converge on similar phenotypes, or phenotypes may be conserved for a particular habitat type. In the dwarf chameleons (Bradypodion) of southern Africa, it has been hypothesized that some lineages have converged on similar phenotypes (ecomorphs) when they occur in habitats with similar vegetation structure. However, the convergence of lineages into ecomorphs has not been explicitly tested across the genus and could be due to other factors such as morphological conservatism or shifts of entire clades to new trait states. To assess these alternatives, we measured functional morphological traits across 24 lineages of Bradypodion and tested for evidence of phenotypic convergence using time-calibrated phylogenies. Our results indicated that many lineages that do not share a common ancestor, but are from similar habitats, have converged on similar phenotypes (i.e., tail length, hand size, foot size, casque height), with ecology showing a stronger influence than evolutionary history. We interpret this as adaptive changes in morphology in response to the constraints imposed by different habitat types.