Temperature constrains diet-induced plasticity in the life-history of an aquatic vertebrate.

Temperature is a major force governing ectotherm life-history. To buffer temperature-driven nutritional imbalances, consumers may engage in selective feeding, thereby altering trait expression and life-history configuration as a consequence of trait-specific energetic and nutritional optima. Yet, the joint effects of temperature and diet on life-history architecture remain poorly understood in vertebrate consumers. We reared Bufo spinosus tadpoles under three temperatures (12 °C, 16 °C, 20 °C) and three diet types (animal-based, plant-based, or choice between both), assessing how selective feeding influences trait performance and life-history plasticity. Increasing temperature altered life-history, accelerated larval development and growth, reducing body mass and condition (SMI), with marginal effects on body length. Dietary effects were trait-specific and temperature-dependent, with the animal diet performing better at 12 °C both in growth rate and body mass but losing this advantage at higher temperatures. Tadpoles offered the choice diet fed selectively, leading to lower assimilation of animal-based at higher temperatures, and generally outperformed tadpoles fed fixed diets. However, selective feeding only partially offset the impacts of higher temperatures. Our results show that increasing temperature canalized life-history trajectories, constraining diet-induced plasticity, and highlight the need to integrate thermal and nutritional drivers in predicting ectotherm responses to climate change.