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The widespread distribution of the freshwater shrimp Paratya australiensis in eastern Australia suggests that populations of this species have been connected in the past. Amphidromy is ancestral in these shrimps, although many extant populations are known to be restricted to freshwater habitats. In this study, we used a fragment of the cytochrome c oxidase I mitochondrial DNA (mtDNA) gene to examine diversity within P. australiensis and to assess the relative importance of amphidromy in its evolutionary history. We hypothesized that if transitions from an amphidromous to a freshwater life history were important, then we would find a number of divergent lineages restricted to single or groups of nearby drainages. Alternatively, if amphidromy was maintained within the species historically, we expected to find lineages distributed over many drainages. We assumed that the only way for divergence to occur within amphidromous lineages was if dispersal was limited to between nearby estuaries, which, during arid periods in the earth's history, became isolated from one another. We found nine highly divergent mtDNA lineages, estimated to have diverged from one another in the late Miocene/early Pliocene, when the climate was more arid than at present. Despite this, the geographic distribution of lineages and haplotypes within lineages did not support the notion of a stepping-stone model of dispersal between estuaries. We conclude that the extensive divergence has most likely arisen through a number of independent amphidromy-freshwater life history transitions, rather than via historical isolation of amphidromy populations. We also found evidence for extensive movement between coastal and inland drainages, supporting the notion that secondary contact between lineages may have occurred as a result of drainage rearrangements. Finally, our data indicate that P. australiensis is likely a complex of cryptic species, some of which are widely distributed, and others geographically restricted.

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Wastewater studies that provide per-capita estimates of consumption (influent) or release (effluent) via wastewater systems rely heavily on accurate population data. This study evaluated the accuracy of Wastewater Treatment Plant (WWTP) reported populations, as well as hydrochemical parameters, against accurate populations from a population census. 104 catchment maps were received from WWTPs, geo-located in geospatial software and overlaid with the smallest area unit of the Australian census, equating to 14.9 million Australians or 64% of the national population. We characterised each catchment for population counts, as well as by age profile, income profile and education level. For a subset of sites, population estimates using hydrochemical parameters BOD, COD and dissolved ammonia were evaluated for accuracy against census populations. Compared to census-based estimates, population estimates provided by WWTP personnel were overestimated by 18% on average. Similarly, hydrochemical-based population estimates had high RSD (> 44%) for BOD, COD and ammonium between sites, suggesting their applicability for use in population estimation may not be appropriate for every WWTP. Surprisingly, 46% of catchments had a skewed age distribution; 6% skewed older and 40% younger. Through this process WWTP catchment populations can be characterised in a way which will enhance the interpretations of percapita estimates.