The systematics and biogeography of the Bearded Greenbuls (Ayes: Criniger) reveals the impact of Plio-Pleistocene forest fragmentation on Afro-tropical avian diversity

The biogeographical history of Afro-tropical lowland forests during the Plio-Pleistocene is characterized by pervasive fragmentation-coalescence cycling due to global climatic oscillations. Vicariance scenarios driven by forest fragmentation have long been hypothesized as major mechanisms for the creation and maintenance of Afro-tropical avian diversity. However, the timing and centre of diversification events remains unclear. We undertook the first molecular phylogenetic and biogeographic investigation of the avian genus Criniger, a group of understory birds endemic to the lowland forests of West and Central Africa. Utilizing DNA from 43 specimens and a combination of molecular and biogeographic methods, we constructed time-calibrated phylogenies and ancestral area estimations. We estimated a widespread origin for the genus, with a basal divergence dating to the late Miocene. All other speciation events were dated to the Pliocene. However, we recovered substantial geographic structuring of genetic diversity, dating to the Pleistocene, within both Western and Central Africa for three species. The biogeographic patterns observed in the genus Criniger are likely the result of allopatric diversification driven by forest fragmentation during the PlioPleistocene. The results of this study indicate that Afro-tropical forests harbour substantially higher levels of cryptic diversity and greater genetic complexity than previously hypothesized.