Squirrel reservoirs of monkeypox virus are sister species separated by the Sanaga River (Cameroon), as are the two main viral clades.

Monkeypox is an emerging infectious disease of unclear zoonotic origin in Africa although increasing evidence suggests that rope squirrels are reservoirs of the monkeypox virus (MPXV). Here, we describe new data on the systematics of rope squirrels (Sciuridae, Funisciurus). Our molecular phylogeny strongly supports the polyphyly of Funisciurus pyrropus, with a Central African clade sister to Funisciurus leucogenys and a West African clade sister to Funisciurus anerythrus. Museum specimens show that the two clades have distinct pelage patterns. We propose therefore to resurrect the name Funisciurus leucostigma for the West African clade. Using reliable taxonomic identifications of georeferenced squirrels, we inferred the ecological niches of the three species of interest. The Sanaga River in Cameroon appears to be the barrier separating both the sister species F. anerythrus and F. leucostigma as well as the sister MPXV clades I and II. This suggests that these two MPXV clades were isolated in Central and West Africa, respectively, due to allopatric squirrel speciation.