Temperature-driven plasticity in nutrient use and preference in an ectotherm

Environmental temperature has strong effects on the rate and efficiency of resource use in ectotherms, but little is known about how changes in temperature influence their diet selection patterns. Changes in temperature may alter the balance of nutrients required by ectotherms by affecting metabolism. In response to temperature changes, ectotherms are predicted to express a preference for a specific nutrient (protein or carbohydrate) to match their altered nutrient requirement. Here, we examined the nutritional consequences of mealworm beetles (Tenebrio molitor L.) that were constrained to diets varying in protein:carbohydrate balance (P:C = 1:5, 1:1, or 5:1) or offered a choice between two nutritionally complementary diets (1:5 vs. 5:1) at four different temperatures (20, 25, 30, or 35 °C). Beetles had high mortality and reduced body mass at higher temperatures. Post-ingestive use efficiencies of both protein and carbohydrate decreased as temperature rose. Warming-driven decrease in carbohydrate use efficiencies occurred most profoundly when carbohydrates were consumed excessively. When given a choice, beetles selected protein and carbohydrate equally at 25 and 30 °C, but exhibited a significant preference for carbohydrate at 35 °C. Since carbohydrate is an immediate source of energy, this warming-driven preference for carbohydrate is explicable as an adaptive response of beetles to meet increased energy needs at high temperature. Beetles exposed to 20 °C ate substantially less food, but preferentially consumed carbohydrate over protein possibly to cope with reduced energy intake. The present findings have implications for the impact of temperature on foraging and resource use in ectotherms.