Aquatic Insect Thermal Responses Vary by Physiological Rate and Diet

ABSTRACT Temperature is an important control on metabolic rate and organismal contribution to ecosystem processes. Many studies have measured aquatic insect thermal performance, but fewer have simultaneously measured thermal responses for multiple physiological rates and examined how these responses are modulated by diet. We examined the effects of temperature and diet on survival probability, development, growth rate and consumption rate in an abundant stream insect shredder, Tallaperla spp. (Plecoptera: Peltoperlidae). We quantified physiological rates of Tallaperla across five temperature treatments (ambient [mean = 10.4°C], +1°C, +2°C, +3°C, +4°C) and two leaf types that differ in nutritional quality ( Rhododendron maximum = higher carbon‐to‐nutrient [C:nutrient] ratio; Acer rubrum = lower C:nutrient ratio) and microbial colonization. Our five‐week experiment took place in outdoor streamside channels ( n = 20) with leaf litter and Tallaperla nymphs collected from nearby streams. Survival probability declined with rising temperatures, particularly later in the experiment, and was lowest at +3°C and +4°C. Insects in these treatments were more likely to develop black wingpads by the end of the experiment than insects in lower‐temperature treatments (ambient, +1°C and +2°C), indicating that insects in higher‐temperature treatments developed more rapidly. Insect growth rates were not related to temperature. Temperature effects did not differ based on diet for survival, development, or growth rates. In contrast, temperature effects on consumption rate depended on diet. Specifically, consumption rates increased with temperature for insects consuming higher‐C: nutrient Rhododendron, but there was no relationship between temperature and consumption rate for insects consuming lower‐C: nutrient Acer . This difference could indicate compensatory feeding by insects in higher‐temperature, high‐C: nutrient litter treatments. Our results highlight variable thermal responses for different physiological rates in an aquatic insect shredder, as well as the potential strategies these organisms may use to cope with higher temperatures. Overall, these findings suggest that shredder physiological rates and population persistence, as well as shredder‐mediated carbon processing in streams, may shift in a warmer world.