Abstract
Cisco (Coregonus artedi) are threatened by climate change and lake eutrophication, and their oxythermal habitat can be assessed with T-DO3, the water temperature at which dissolved oxygen equals 3 mg.L-1. We assessed the influence of T-DO3 on cisco habitat use, genetic diversity, diets, and isotopic niche in 32 lakes ranging from oligotrophic to eutrophic. Results showed that as T-DO3 increased, cisco were captured higher in the water column, in a narrower band, with higher minimum temperatures and lower minimum dissolved oxygen. T-DO3 was also negatively related to cisco allelic richness and expected heterozygosity, likely driven by summer kill events. Moreover, T-DO3 influenced the isotopic niche of cisco, as fish captured deeper were more depleted in delta C-13 and more enriched in delta N-15 compared to epilimnetic baselines. Lastly, cisco in high T-DO3 lakes consumed more Daphnia , had fewer empty stomachs, and achieved larger body size. Our work identifies specific characteristics of cisco populations that respond to climate change and eutrophication effects and provides a frame-work for understanding responses of other cold-water species at the global scale.