Integrative effects of warming and contaminants on the physiology and behaviour of coldwater stenotherm caddisflies

Aquatic ecosystems globally are increasingly affected by both natural and anthropogenic stressors. High-altitude systems are particularly vulnerable due to high specialization of organisms to survive specific conditions, making them especially sensitive to environmental changes related to rising temperatures and chemical pollution from runoff and wastewater discharge. These stressors can significantly alter the physiology, behaviour, and population dynamics of aquatic organisms. Our study investigated the individual and combined impacts of emerging contaminants and elevated water temperature (as a proxy for climate change) on the metabolome, body weight, and behaviour of cold-water stenotherm caddisfly larvae, Drusus croaticus. We conducted a 21-day factorial microcosm experiment with four treatments: control, emerging contaminants (ECs – 8 pharmaceuticals and 1 industrial chemical), elevated temperature (+4°C), and a multiple stressor treatment combining both warming and contaminants. Our results showed that the metabolome of D. croaticus larvae was primarily affected by elevated temperature and the combination of warming and contaminants, reflecting significant metabolic stress. Larvae in the elevated temperature and multiple stressor treatments exhibited significantly higher locomotor activity, moving more than controls. This increased activity appears to have contributed to a marked decrease in body weight compared to controls and larvae exposed to contaminants alone. These findings suggest a trade-off between activity and growth under stress conditions, where increased energy expenditure on movement may come at the cost of reduced growth. More specifically, elevated temperature inhibited growth and triggered hyperactivity. Additionally, the correlation between metabolomic shifts and behavioural changes indicates that metabolic responses to stress develop early, while behavioural effects may take longer to manifest. Our findings give important insights into how multiple stressors affect stenotherm caddisfly species, which are crucial for maintaining the integrity of both aquatic and terrestrial food webs in higher altitude environments. Hence, they underscore the urgent need for conservation measures to protect biodiversity in vulnerable ecosystems impacted by warming and pollution.