Species boundaries and possible hybridization between the black mongoose (Galerella nigrata) and the slender mongoose (Galerella sanguinea)

► Past climatic fluctuations influenced the divergence of two sympatric sister species. ► Genetic sequences of Galerella nigrata form distinct monophyletic clades. ► Divergence of G. nigrata from G. sanguinea occurred 3.85-4.27 million years ago. ► Estimated divergence time coincides with a period of global cooling and strong aridity. ► The two species have not yet undergone complete reproductive isolation.