A tale of the nearly tail-less: the effects of Plio-Pleistocene climate change on the diversification of the African avian genus Sylvietta

Sylvietta is a broadly distributed group of African species inhabiting a wide range of habitats and presents an interesting opportunity to investigate the historic mechanisms that have impacted the biogeography of African avian species. We collected sequence data from 50 individuals and used model-based phylogenetic methods, molecular divergence estimates and ancestral area estimates to construct a time-calibrated phylogeny and estimation of biogeographic history. We estimate a southern African origin for Sylvietta, with an initial divergence splitting the genus into two clades. The first consists of arid-adapted species, with a southern African origin and subsequent diversification north into Ethiopia-Somalia. The second clade is estimated as having a Congolian forest origin with an eastward pattern of colonization and diversification as a result of Plio-Pleistocene forest dynamics. Additionally, two members of the genus Sylvietta display interesting patterns of intraspecific diversification. Sylvietta rufescens is an arid-adapted species inhabiting southern Africa, and we recover two subclades with a divergence dating to the Pleistocene, a unique pattern for avian species which may be explained via isolation in arid habitat fragments in the early Pleistocene. Second, Sylvietta virens, a species endemic to Afro-tropical forests, is recovered with geographically structured genetic diversification across its broad range, an interesting result given that recent investigations of several avian forest species have found similar and substantial geographically structured genetic diversity relating to Plio-Pleistocene forest fragmentation. Overall, Plio-Pleistocene habitat cycling played a significant role in driving diversification in Sylvietta, and this investigation highlights the substantial impact of climate-driven habitat dynamics on the history of sub-Saharan species.