Origin of Bannerman’s Turaco Tauraco bannermani in relation to historical climate change and the distribution of West African montane forests

Abstract

We determined the systematic relationships and approximate divergence time of Bannerman’s Turaco Tauraco bannermani and used this information to test whether the origin and distribution of this species and its closest relatives are associated with the effects of historical climate change on forest habitats in West Africa. We collected mitochondrial DNA (mtDNA) sequence T. bannermani and combined this with previously published data to (1) generate a phylogeny for 22 of the 23 turaco species and (2) estimate approximate divergence times among species. The mtDNA data provide strong support for a clade comprising T. bannermani, the morphologically similar T. erythrolophus, and T. leucolophus. Genetic distances suggest that the mitochondrial lineages of these species diverged in the late Pliocene concomitant with increasingly arid and variable palaeoenvironmental conditions. We suggest that palaeoclimate change sundered a more widespread ancestral population associated with montane forests, giving rise to three allopatric species. More recent forest contraction during the past 100 000 years has likely led to increasingly restricted ranges for T. bannermani and T. erythrolophus. In contrast, T. leucolophus has maintained a much larger range, perhaps by adapting to savanna and submontane habitats. Finally, we suggest that the current dependence of Bannerman’s Turaco on montane forests and its restricted range in Cameroon are largely the result of drier conditions in the late Pleistocene. The fragmented modern population is now highly vulnerable to extinction due to ongoing habitat loss.

Ostrich 2009, 80(1): 1–7