Relationships of the New Guinean subspecies, Gymnorhina tibicen papuana, of the Australian Magpie: an assessment from DNA sequence data

Abstract

Although it is well understood that New Guinea and Australia are essentially one landmass that connects periodically during sea-level fluctuations, the biogeographic history and effects of environmental change for species that span the two islands has not been studied in depth. The New Guinean subspecies of the Australian Magpie, Gymnorhina tibicen papuana, is known to share morphological traits with subspecies from north-western and south-western Australia (G. t. longirostris and G. t. dorsalis, respectively). Here, we use molecular data to explore the relationships of the New Guinean subspecies. Mitochondrial DNA supports a close relationship with a previously identified Australian phylogroup, which includes the two western Australian subspecies G. t. longirostris and G. t. dorsalis and western populations of what has been recognised as a northern subspecies G. t. eylandtensis. We infer that the formation of land bridges, most likely during the most recent glacial period, allowed movement of magpies between New Guinea and Australia but not, evidently, involving Cape York Peninsula, which is that part of Australia closest today to the range of G. t. papuana. Dispersal would have ceased following the most recent sea-level rise 16 500 years ago. Overall, our study is consistent with a hypothesis that savannah-associated species dispersed between Australia and New Guinea via a western route across land bridges associated with the Sahul Shelf.