Coalescent models reveal the relative roles of ancestral polymorphism, vicariance, and dispersal in shaping phylogeographical structure of an African montane forest robin

Although many studies have documented the effect of glaciation on the evolutionary history of Northern Hemisphere flora and fauna, this study is the first to investigate how the indirect aridification of Africa caused by global cooling in response to glacial cycles at higher latitudes has influenced the evolutionary history of an African montane bird. Mitochondrial DNA sequences from the NADH 3 gene were collected from 283 individual Starred Robins (Pogonocichla stellata, Muscicapoidea). At least two major vicariant events, one that separated the Albertine Rift from all but the Kenyan Highlands around 1.3–1.2 Myrs BP, and another that separated the Kenyan Highlands from the northern Eastern Arc, and the northern Eastern Arc from the south-central Eastern Arc between 0.9 and 0.8 Myrs BP appear to underlie much of the observed genetic diversity and structure within Starred Robin populations. These dates of divergence suggest a lack of recurrent gene flow; although the Albertine Rift and south-central Eastern Arc share haplotypes, based on coalescent analyses this can confidently be accounted for by ancestral polymorphism as opposed to recurrent gene flow. Taken collectively, strong evidence exists for recognition of four major ancestral populations: (1) Kenyan Highlands (subspecies keniensis), (2) Albertine Rift (ruwenzori), (3) northern Eastern Arc (helleri), and (4) south-central Eastern Arc, Ufipa and the Malawi Rift (orientalis). The estimated divergence times cluster remarkably around one of the three estimated peaks of aridification in Africa during the Plio-Pleistocene centred on 1 Myrs BP. Further, time to most recent common ancestor (TMRCA) estimates (1.7–1.6 Myrs BP) of gene divergence between the Albertine Rift and the other montane highlands corresponds closely with a second estimated peak of aridification at about 1.7 Myrs BP. Collectively, these results suggest that aridification of Africa in response to glaciation at higher latitudes during the Pleistocene has had a profound influence on montane speciation in east and central Africa.