The impact of historic isolation on the population biogeography of Melita plumulosa (Crustacea: Melitidae) in eastern Australia

The genetic structure of populations is impacted by environmental factors of both natural and anthropogenic origin. These factors can affect dispersion, gene flow and selective pressures. We test whether natural environmental factors or anthropogenic factors influence the genetic structure of the amphipod, Melita plumulosa (Crustacea: Melitidae), which serves as an indicator of environmental health in estuaries along eastern Australia. Sequence data from one mitochondrial and two nuclear loci were collected and analyzed from eight geographically distinct populations spanning the known distribution of this species. We identified two major clades corresponding to the east and south coasts of Australia, and populations also largely grouped according to geography within each clade. Population differentiation indicated all sampling localities to be distinct from one another and sequence divergences suggested ancient divergence, with the deepest genetic divergences between the eastern and southern populations. Reproductive compatibility did not indicate cryptic speciation between populations. Sequence divergence and population differentiation suggest historic geographic isolation dating back to the Pleistocene to have influenced the population biogeography of M. plumulosa.