Comparing perch availability and perch use between African dwarf chameleon (Bradypodion) ecomorphs

Adaptation to different environments can lead to local adaptations that facilitate morphological divergence between closely related taxa, potentially leading to speciation. Quantifying habitat variation can thus provide valuable insights into evolutionary processes. Arboreal dwarf chameleons of the genus Bradypodion exhibit 3 distinct ecomorphological forms: forest, shrub, and "little brown chameleons" (LBCs). It is assumed these ecomorphs are the result of convergence among species that are in similar habitats regardless of ancestry, or in some cases, morphological conservatism and retention of an ancestral form that is adapted to a shared habitat type. If so, then the habitat of different ecomorphs would differ in vegetation structure. Our results show that vegetation structure in fynbos/grassy habitats is characterized by significantly narrower perches than shrubby habitats, but both have a largely vertical perch orientation. In contrast, forests have significantly fewer vertical perches than fynbos/grassy habitats with significantly thicker diameter perches. Accordingly, LBC and shrub species used more vertically oriented perches than forest species, suggesting that perch use corresponds with the most widely available perch angles. Although LBC chameleons used the smallest diameter perches, when corrected for body size, there was no difference in perch diameter among ecomorphs. These results suggest that the body size of LBC chameleons is constrained by the prevalence of small-diameter perches in their habitat. Species in habitats with wider perches attain larger body size. These findings support the notion that variation in perch structure is critical for phenotypic convergence that has resulted in the 3 Bradypodion ecomorphs.