Evolution of the Australasian songbird fauna

DNA analyses have revolutionised our understanding of the origin and evolution of the world’s avifauna, and have identified a central role for the Australasian region in the evolutionary history of the Aves. The Australasian region has been conclusively shown to be the centre of origin for the songbirds, or oscines. The long endemic history of the oscine fauna in Australia provides an excellent opportunity to investigate how lineages radiate and adapt through major long-term changes in climatic and environmental conditions. DNA studies have revealed that the Australasian oscines are over-lumped and that the number of small genera being recognised is increasing. This contrasts with the presence of a larger number of highly speciose genera in the northern hemisphere. These contrasting patterns suggest that following the initial establishment and diversification within a region, lineages undergo a period of adaptation and evolutionary divergence with limited diversification or speciation. DNA analyses have also revealed intricate links between songbird lineages across the Indo-Pacific region. These studies have shown that dispersal has played a major role in speciation across the island archipelagos, whereas biogeographical barriers and vicariant events have been more important in shaping diversity within the continental land-masses. Long-distance, bidirectional trans-oceanic dispersal, involving Africa and Australasia has been found to have featured in explaining the distribution of several oscine lineages in the ‘core’ Corvoidea.