Anti-predator syndrome: modeling and testing behavioral, morphological, and life-history plasticity in tadpoles

Tadpoles exhibit various behavioral, morphological, and life-history adaptations to evade predators or escape their attacks. These traits are costly, and their expression involves trade-offs, resulting in predictable patterns of phenotypic integration. Within individuals, these patterns arise from plastic adjustments of traits in response to extrinsic factors, such as predation risk. In contrast, among individuals, they reflect differences in both extrinsic and intrinsic factors, such as resource availability or genetic quality. Here, we tested the hypothesis that these patterns of integration, both within- and among individuals, directly depend on how tadpoles manage their energy budgets. Our approach was both theoretical and empirical. We created an optimality model for tadpole life history. This model focused on two key parameters: the time spent feeding, which determined both the tadpole’s daily energy budget and the probability to encounter predators; and the portion of the daily energy budget allocated to developing defensive traits, which increased the probability of escaping predator attacks, but it decreased growth and development rates. The model also considered two patterns of among-individual variation: variation in metabolic efficiency and metabolic capacity. From this model, we derived predictions about trait co-variation within and among individuals. To test these predictions, we conducted an experiment using tadpoles of the brown frog, Rana dalmatina. We raised siblings either in the presence or absence of predators and we repeatedly tested them in arenas both with or without caged predators. At the individual levels, we observed consistency between theoretical and empirical results: tadpoles raised with predators exhibited reduced activity, developed larger defensive traits (i.e. deeper tails and faster movements), grew more slowly and took longer to metamorphose than their control siblings. At the among-individual level, in both ontogenetic treatments, the observed pattern of covariation supported the hypothesis that tadpoles differed more in metabolic efficiency than in metabolic capacity.