Impact of temperature and hypoxia on the size and survival of aquatic insects

Abstract

Understanding size–temperature relations is crucial for the conservation of aquatic insects. Here, we present the results of mesocosm experiments designed to elucidate the interactions between water temperature, hypoxia, and body size of the aquatic insect Chironomus riparius (Meigen, 1804). We hypothesised that the combination of high temperature and hypoxia will lead to a reduction in the size of larvae and pupae of aquatic insects. To this end, we compared the body size and survivability of C. riparius in six experimental treatments: three at 20°C, with high, medium and low oxygen concentration, and three at 30°C, with the same three levels of oxygen concentrations. Our experiments showed that C. riparius pupae were significantly smaller at 30°C treatments with medium and low oxygen levels than in the rest of the treatments. No significant reduction in pupal size was observed in the 30°C treatment with high oxygen content. No significant differences in larval size were observed between the treatments. However, we detected reduced larval survivability in the 30°C treatments with medium and low oxygen levels compared to the other treatments. Our results corroborate the original hypothesis that it is low oxygen availability, rather than increased temperature per se, that leads to size reduction in aquatic insects. These findings suggest that increasing temperatures worldwide will negatively impact (some) aquatic insects' fitness through the size diminution induced by hypoxia.