Historic and current genetic population structure in two pond-dwelling macroinvertebrates in massively altered Australian woodland landscapes

Aquatic ecosystems around the world have been massively altered through vegetation clearance and changed flow regimes accompanying agricultural development. Impacts may include disrupted dispersal for aquatic species. We investigated this in lentic (standing) waterbodies in agricultural and predominantly forested landscapes of the boxironbark region of central Victoria, Australia. We hypothesised that higher representation in forested than agricultural landscapes (i.e. ‘forest-bias’) for a species may reflect an ability to disperse more easily through the former, resulting in lower genetic structure in forested than in agricultural landscapes. Conversely, ‘cosmopolitan’ species would show no difference in genetic structure between landscape types. Molecular genetic analyses of a forest-biased diving beetle, Necterosoma wollastoni, and a cosmopolitan waterboatman, Micronecta gracilis, revealed the following, for both species: (1) no evidence for long-term barriers to gene flow in the region, (2) lack of contemporary genetic differentiation over 30 000 km2 and (3) random distribution of related genotypes in space, implying that neither forest nor farmland inhibits their dispersal in a concerted fashion. Taken together, these results indicate very high gene flow and dispersal in the past and present for both these species. Massive landscape change may have little impact on movement patterns of lentic invertebrates that have evolved high dispersal capabilities.