The impact of Pleistocene changes of climate and landscape on Australian birds: a test using the Pied Butcherbird (Cracticus nigrogularis)

Widespread cyclic aridity during the Pleistocene is hypothesised to have had a significant impact on widespread Australian birds causing range-wide contractions to historical refugia and population differentiation while in isolation. In this study we tested a priori hypotheses for the impact of Pleistocene climatic and edaphic changes on the population history of the widespread Australian Pied Butcherbird (Cracticus nigrogularis). Analysis of mitochondrial DNA sequences from 55 individuals of C. nigrogularis revealed low genetic diversity, poor geographical structure and signatures of a recent demographic expansion. In contrast with long-standing biogeographical hypotheses, our data suggest that C. nigrogularis was likely to have been restricted to multiple refugia across its current range rather than undergoing range-wide contractions to one or few refugia. In addition, we found no evidence for the Carpentarian Barrier of northern Australia having limited dispersal in C. nigrogularis, which contrasts with predictions from intraspecific taxonomy and with population structures of several other bird species. Our data add to the increasing number of phylogeographical studies of widespread Australian birds that show evidence of maintaining large effective population sizes despite widespread aridity, as well as species-specific, rather than ecosystem-wide, responses to Pleistocene climatic changes and biogeographical barriers.