Out of southern Africa: Origins and cryptic speciation in Chamaeleo, the most widespread chameleon genus

Abstract

Molecular phylogenetics and the application of species delimitation methods have proven useful in addressing limitations associated with morphology based taxonomy and have highlighted the inconsistencies in the current taxonomy for many groups. For example, the genus Chamaeleo, which comprises 14 species with large distributions across mainland Africa and parts of Eurasia, exhibits relatively minor phenotypic differentiation between species, leading to speculation regarding the presence of cryptic diversity in the genus. Therefore, the aims of the present study were to construct a robust and comprehensive phylogeny of the genus and highlight potential species-level cryptic diversity. Additionally, we sought to ascertain the most likely biogeographic origin of the genus and understand its spatio-temporal diversification. Accordingly, we made use of species delimitation methods (Bayesian and divergence based) to investigate the extent of cryptic diversity in Chamaeleo, and applied an ancestral area reconstruction to examine the biogeographic origin of the group. Our phylogenetic analyses suggested the presence of at least 18 taxa within Chamaeleo. Notably, three taxa could be recognised within C. dilepis, none of which are equivalent in context with any of the currently described subspecies. There were also three taxa within C. gracilis and two within C. anchietae. The single available tissue specimen identified as C. necasi was embedded within the C. gracilis clade. Our ancestral area reconstruction points to a southern African/Zambezian origin for Chamaeleo, with diversification beginning during the cooling and aridification of Africa that characterised the Oligocene Epoch, ca. 34–23 Mya (Million years ago). Species-level diversification began in the Miocene Epoch (ca. 23–5 Mya), possibly tracking the aridification that triggered the shift from forest to more open, mesic savanna for most clades, but with tectonic events influencing speciation in a Palearctic clade. These findings lay the foundation for a future integrative taxonomic re-evaluation of Chamaeleo, which will be supported with additional lines of evidence before implementing any taxonomic changes.