Molecular systematics and evolutionary history of akalats (Genus Sheppardia): A pre-Pleistocene radiation in a group of African forest birds

The African forest robins (akalats) of the genus Sheppardia are represented by eight forest-dwelling species with restricted distributions in tropical Africa. All but three are strictly montane, inhabiting isolated highland a reas in eastern and western Africa. Due to their subtle plumage variation a nd almost wholly allopatric distribution, determining systematic relationsh ips based upon morphology has proven difficult. However, akalats, due to th eir distribution, offer an ideal opportunity to test models of speciation w ithin tropical forests. We therefore investigated the phylogeny of species of this genus from presently sampled regions of their distribution using mt DNA sequence analysis. We found that the monophyly of described species, ev en from disjunct populations, is well supported. However, relationships amo ng species is generally poorly resolved, with support given only to the pai red relationships S. montana/S. lowei, S. bocagei/S. gunningi, and S. aequa torialis/S, cyornithopsis. This dataset lent support to S. montana and S. l owei representing a superspecies. All species appear to have evolved rapidl y from a common ancestor around the Miocene/Pliocene transition, a time of the last uplift of East Africa's montane region. Surprisingly, intraspecifi c radiations suggest a far more recent population expansion in the upper Pl eistocene, concordant with major climatic variation and vegetational change s, We discuss the implications of our results in the light of previous disc ussions of the montane speciation model. (C) 2000 Academic Press.