Transcriptomics in Ecotoxicology: Characterizing the Effects of Contaminants and Environmental Parameters on Aquatic Populations
Characterizing the potential impacts of chemical stressors from the molecular level to the population level is critical in understanding the risks of contaminants to wildlife. Use of transcriptomics is a powerful tool that may be used to identify the mechanisms of action of a chemical and, thus, to predict ecological risk through an adverse outcome pathway approach. In the present study, fish population declines thought to be a result of estrogenic contaminants from wastewater treatment effluent were explored using molecular- to population-level endpoints. Population declines were instead found to be correlated with increased water temperatures indicating that environmental stressors may alter ecosystem health in addition to contaminants. It is likely that repeated biannual sampling also contributed to population declines to some degree, warranting the development of non-lethal, catch and release sampling methods. To assess effects of environmental factors and limit lethal sampling of populations for molecular endpoints, the toxicogenomic analysis of epidermal mucus was evaluated as a non-lethal assessment tool. Using the Canadian Experimental Lakes Area, mucus from four fish populations residing in different lakes underwent RNA sequencing. Results indicated that RNA sequencing of mucus was able to discern unique patterns of gene expression among fish populations that correlated with environmental variables, such as productivity, dissolved oxygen, and alkalinity. Thus, toxicogenomic analysis of mucus was identified as a useful tool to assess molecular effects of environmental factors on fish populations. To further develop the use of mucus for ecotoxicological studies, mucus was collected and sequenced from fish before and after additions of diluted bitumen (dilbit) into one of these lakes. Transcripts associated with oil exposure were altered in mucus of dilbit-exposed individuals, suggesting that transcriptomic analysis of mucus may be used as a non-lethal method for exposure assessment to environmental contaminants. Overall, this work explored the use of transcriptomic tools to assess exposure to environmental and chemical stressors in wild populations and identified transcriptomics of mucus as an effective non-lethal toxicogenomics-based assessment tool.