Evolution and maintenance of divergent lineages in an endangered freshwater fish, Macquaria australasica.
Genetic diversity is essential for organisms to evolve to changes in their environment. Although geologically relatively stable, southeastern Australia has experienced significant changes in landscape and climate conditions to which species have evolved. For freshwater taxa, variable hydrological regimes and habitat availability have been very strong determinants of current species distribution and population structure. We have conducted a range wide phylogeographical study of Macquarie Perch, Macquaria australasica, in order to understand the relationship between landscape and freshwater fish evolution in southeastern Australia, and to assess the levels of genetic diversity and divergence in this endangered species. We found 46 mtDNA control region haplotypes from 35 sampling locations with up to 6% sequence divergence between lineages. Phylogenetic reconstruction indicates that the species originated on the coast, east of the Great Dividing Range and subsequently colonised inland to the Murray-Darling Basin, west of the Great Dividing Range. Mismatch analysis suggests that this colonisation may have been followed by demographic expansion of the population approximately 536kya. Nested clade and IM analyses also support a series of range expansions and fragmentations across the species range during the Pleistocene. We conclude that the unexpected high levels of diversity and divergence observed in M. australasica may be due to the interacting factors of habitat specificity, localised recruitment and Pleistocene climate fluctuations. The comprehensive phylogeographical approach used here has given valuable insight into the aspects of M. australasicas biology and its interactions with the environment that may be critical to its conservation management.