Freshwater ecosystem monitoring, critical for long-term management of impacted areas, relies upon accurate taxonomy, sufficient taxonomic resolution and can benefit from forewarning of sublethal impacts on populations. Within the Chironomidae (Diptera), the global genus Cricotopus Wulp has long been taxonomically confusing. The poorly known Australian fauna occupies a wide range of lotic freshwater ecosystems with marked variation among species, especially in their pollution tolerance. Although immature stages are collected routinely in surveys, tolerance is generalised at the genus level.This presentation summarizes research that explored: a) the systematics of the genus; b) the phylogenetic pattern of pollution tolerance; c) comparative larval transcriptomics between three sympatric species; and, d) differential gene expression among populations of a single species from habitats that differ in ecosystem health.
For a) and b), we used a multilocus molecular phylogenetic approach and sampled all but one Australian species. Cricotopus was paraphyletic through inclusion of monophyletic Paratrichocladius, which we collapse as a subgenus of Cricotopus. However, morphological species concepts were largely corroborated. There was no significant relationship between a species’ phylogenetic position and its pollution tolerance, suggesting that sensitive and restricted taxa have diversified into more narrow niches from a widely tolerant ancestor. For c) and d), we sampled larval transcriptomes from two locations near Brisbane at which they co-occur. Comparative analyses suggest broad similarities among species; however, some key differences were observed, involving chemorepellent, antioxidant, and fat body nutrient storage genes. Within a single species, differential expression was not associated with ecosystem health; instead, the greatest trend was between season, specifically start- and end-wet season rainfall. Higher water levels (end-wet) were characterised by upregulation of detoxification genes, suggesting significant influence of runoff, whereas developmental genes dominated the start-wet period. Taken together, this research provides important insight into the evolution of pollution tolerance in Australian Cricotopus.