Diet-induced plasticity modifies relationships between larval growth rate and post-metamorphic behavior and physiology in spadefoot toads

It has frequently been hypothesized that among-individual variation in behavior and physiology will correlate with life history traits, yet the nature of these correlations can vary. Such variability may arise from plasticity in trait development, which can amplify or attenuate trait correlations across different environments. Using the Mexican spadefoot toad (Spea multiplicata), we tested whether relationships between larval growth rate and post-metamorphic behavior or physiology are influenced by a key mediator of developmental plasticity: larval diet type. Spea multiplicata larvae develop on two alternative diets, with slower growing omnivores feeding on detritus and faster growing carnivores consuming live fairy shrimp. We found that correlations between larval growth rate and post-metamorphic behavior and physiology differed by diet type. Among detritus feeders, faster growing larvae developed into juvenile frogs that were not only bolder but also had higher hypothalamic-pituitary-interrenal axis reactivity (an indicator of stress responsiveness) and longer telomeres, suggesting greater somatic maintenance. In contrast, among shrimp feeders - which exhibited faster growth overall - larval growth rate was less strongly correlated with juvenile behavior and physiology, indicating that a shift from omnivory to carnivory can attenuate trait correlations among individuals. Overall, our study suggests that developmental plasticity induced by different diet types can modify relationships between life history traits and individual behavior or physiology.