Antipredator syndrome: modelling and testing behavioural, morphological and life history plasticity in tadpoles

Tadpoles show various behavioural, 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 in 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 examined two key parameters: the time spent feeding, which determined both the tadpole’s daily energy budget and the probability of encountering predators, and the portion of the daily energy budget allocated to developing defensive traits. While this distribution increased the likelihood of avoiding predator attacks, it also 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 covariation 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 and without caged predators. We observed a consistent relationship between theoretical and empirical findings at the individual level. Tadpoles that were raised with predators showed reduced activity, developed larger defensive traits (such as deeper tails and faster movements), grew more slowly and took longer to metamorphose than their control siblings. In both ontogenetic treatments, the observed among-individual covariation pattern supported the idea that tadpoles differed in metabolic efficiency rather than metabolic capacity.