The impact of rainforest area reduction in the Guineo‐Congolian region on the tempo of diversification and habitat shifts in the Berlinia clade (Leguminosae)

Abstract

AbstractAimThe Guineo‐Congolian region in Africa constitutes the second largest area of tropical rainforest (TRF) in the world. It covered an estimated 15–22 million km2 during the late Miocene (55–11 Ma) and it has experienced since a declining trend, currently reaching 3.4 million km2, associated with increasing aridification and the replacement of TRF by savanna habitats. Here, we examine whether rainforest area contraction led to a decrease in net diversification rates linked to increasing extinction, or if it is associated with increasing opportunities for allopatric or ecological speciation during periods of forest fragmentation.LocationTropical Africa, Guineo‐Congolian region.TaxonAnthonotha, Englerodendron, Berlinia clade (Leguminosae).MethodsWe used a target enrichment approach combined with a complete data set representing all genera within the Berlinia clade. We combined phylogenomic, dating estimates, habitat reconstruction and diversification rate analyses to infer the effect of change in rainforest area coverage at two taxonomic levels: among genera, and within Anthonotha and Englerodendron.ResultsWe recovered fully resolved and well‐supported relationships among all genera and among species within the two genera. Most genera (87.5%) diverged before the Pleistocene, but Anthonotha and Englerodendron diversified recently, during the most recent cycles of forest contraction and expansion of the Pleistocene.Main conclusionsOur results suggest that the Berlinia clade displays an overall trend of accumulation of species over evolutionary time, suggesting the reduction in TRF area has not decreased net diversification rates. Most habitat shifts to savanna occurred in the Miocene, with no major habitat shifts during the most recent phases of forest expansion–contraction in the Pleistocene. Shifts in habitat from lowland forest to savanna did not trigger diversification rates, but habitat fragmentation might have increased diversification rates through allopatric speciation.