Abstract
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.
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