Molecular phylogenetics, biogeography and patterns of limb loss in the genus Scelotes (Squamata: Scincidae)

The evolution of a snake-like limbless morphology has occurred many times across the squamate tree of life and has been particularly prevalent in the Family Scincidae. Within Scincidae, several genera contain species that are limbed, limb reduced, and limbless, including the genus Scelotes, which comprises 22 species of fossorial and semi-fossorial skinks distributed across southern Africa. Although Scelotes provides an excellent opportunity to investigate patterns of limb loss within a group of closely related species, to date there have been no genus-wide phylogenetic studies that include species from both eastern and western southern Africa. Here we provide a divergence dating phylogenetic analysis of Scelotes that includes 18 of 22 recognised species. Additionally, we conduct ancestral state reconstruction to examine patterns of limb loss across the genus. We find that eastern and western species groups are not reciprocally monophyletic, and we suggest that diversification within major clades may be related to the interplay between habitat heterogeneity and the evolution of limblessness. Ancestral state reconstructions suggest that there were multiple independent instances of limb loss in the genus, and potential limb gain, although there are caveats associated with this result, including difficulties capturing developmental complexities underlying trait evolution in the model parameters. Overall, these results can serve as a roadmap for future studies of trait evolution with the genus.