Evolutionary relationships among blue- and black-plumaged populations of the white-winged fairy-wren (Malurus leucopterus)

The white-winged fairy-wren (Malurus leucopterus) exhibits striking plumage colour variation between the Australian mainland and two islands (Dirk Hartog Island and Barrow Island) off the coast of Western Australia. Adult males on the mainland are bright blue with white wings and adult males on the two islands are black with white wings. To examine evolutionary relationships within this species, we sequenced 980 base pairs of two mitochondrial genes from 34 individuals from both islands and five mainland sites. Birds on Barrow Island were the most genetically distinct. Specimens from Dirk Hartog shared a unique character with, and were most similar to, birds from the Western Australian mainland. The black-and-white-plumaged subspecies from the two islands were not each other's closest relatives. Mapping of plumage evolution produced two equally parsimonious hypotheses: (1) black plumage arose from blue plumage convergently on the two islands, or (2) black plumage arose from blue plumage once and was followed by a re-evolution of blue plumage in mainland Western Australia birds. Levels of genetic differentiation in this species were low but genetic differentiation was discovered between morphologically identical eastern and western populations of the mainland subspecies, which is evidence for a current barrier to gene flow on mainland Australia.