Lack of phylogeographic structure in three widespread Australian birds reinforces emerging challenges in Australian historical biogeography


*Leo Joseph, Australian National Wildlife Collection, CSIRO Sustainable Ecosystems, GPO Box 284, Canberra, ACT 2601, Australia.


Aims  Building on molecular studies of widespread Australian vertebrates, we tested whether each of three widespread Australian bird species, namely the singing honeyeater, Lichenostomus virescens, spiny-cheeked honeyeater, Acanthagenys rufogularis (Passeriformes: Meliphagidae), and black-faced woodswallow, Artamus cinereus (Passeriformes: Artamidae), has undergone a recent (Pleistocene) range expansion across the Australian continent. We related the findings to the presence or absence of geographic variation in each species’ external phenotype and whether historical or non-historical factors have been involved in generating variation.

Methods  A total of 92 specimens of the three species were collected from, as far as possible, the same localities across Australia. They were sampled for mitochondrial DNA (mtDNA) diversity in the 1041 base pairs of the ND2 gene, and these data were analysed with nucleotide diversity statistics, unrooted networks, nested clade analysis, and tests of range expansion or stability.

Results  Range expansions could not be rejected in any of the species in our study. Each had low, geographically unstructured nucleotide diversity. Patterns of geographic variation in the singing honeyeater's and, to a lesser extent, the black-faced woodswallow's external phenotypes are not correlated with mtDNA diversity in ND2.

Main conclusions  Our study adds to the increasing number of data sets suggesting the apparent prevalence of Pleistocene population expansions in widespread Australian birds. Furthermore, it shows that observable geographic structure may evolve very quickly, in response either to environmental gradients or to historical factors that operated too recently to be detected by ND2 sequences (e.g. in the singing honeyeater). Conversely, we have shown that a species that has had a recent population expansion need not necessarily be geographically invariant. To understand fully the interplay between vicariance and dispersal in the history of widespread Australian arid-zone birds, or between the historical and non-historical origins of their differentiation, carefully conducted case-by-case molecular studies will be necessary. Only then will biogeographical patterns and the processes that led to them emerge. Study of the historical biogeography and the more recent population history of Australian arid-zone birds has reached a point where mtDNA-based studies, while still informative and contributing to a growing data base of such work, should be complemented with data from multiple, rapidly evolving nuclear loci.