Temperature outweighs diet in shaping developmental performance in two cricket species via growth delays and physiological limits

Understanding how chronic environmental stressors shape animal development is essential for predicting ecological responses and optimizing rearing systems. This perspective complements the use of short-term tolerance assays, which overlook the cumulative effects of sustained stress. Temperature and nutrition affect key life-history traits such as growth, development rate and survival. While both factors have been widely studied, their relative impacts are not clearly defined. We investigated how constant temperature (26-41°C) and dietary protein-to-carbohydrate (P:C) ratio (0.15-2.18) influence development in two cricket species, Acheta domesticus and Gryllodes sigillatus. Growth trajectories were modelled using a unified logistic equation to estimate asymptotic mass and maximum growth rate, thereby capturing the growth trajectory in a simplified and interpretable way, enabling comparisons across treatments. Asymptotic mass was combined with developmental rate and survival to calculate a composite metric of developmental performance. Developmental performance peaked at 35°C but fell at thermal extremes as a result of delayed development (in cold) or reduced mass and survival (in heat). Diet had more modest effects, as performance was stable across most P:C ratios, and only declined at extreme imbalances. Notably, the performance cost of the most unbalanced diets was comparable to a 4-5°C shift from thermal optimum. Our results demonstrate that temperature, more than diet, drives variation in developmental performance during ad libitum feeding. This integrative framework provides a robust approach to quantify environmental sensitivity, define performance limits and guide us toward the mechanisms underlying those limits and/or performance trade-offs.