Genome-Wide Stress Responses to Copper and Arsenic in a Field Population of Daphnia.

Over the past decade, significant advances have been made to unravel molecular mechanisms of stress response in different ecotoxicological model species. Within this study, we focus on population level transcriptomic responses of a natural population of Daphnia magna Straus, (1820), to heavy metals. We aim to characterize the population level transcriptomic responses, which include standing genetic variation, and improve our understanding on how populations respond to environmental stress at a molecular level. We studied population level responses to two heavy metals, copper and arsenic, and their binary mixture across time. Transcriptomic patterns identified significantly regulated gene families and genes at the population level including cuticle proteins and resilins. Furthermore, some of these differentially regulated gene families, such as cuticle proteins, were also significantly enriched for genetic variations including SNPs and MNPs. In general, genetic variation was observed in specific gene families, many of which are known to be involved in stress response. Overall, our results indicate that molecular stress responses can be identified within natural populations and that linking molecular mechanisms with genetic variation at the population level could contribute significantly to adverse outcome frameworks.