A comparative study of activity levels in larval anurans and response to the presence of different predators

Abstract

Activity level is a key behavioral trait in many animals which mediates a trade-off between finding food and avoiding predation. Optimal activity level will therefore depend on environment, and plasticity in response may increase fitness (if an organism encounters multiple environments in a lifetime). One group in which activity level, and its relationship to foraging and predation risk, has been well studied is larval anurans. Anurans inhabit a range of distinct freshwater aquatic community types that are created by differences in pond permanency and top predator. Species segregate across these pond types and therefore tadpoles from different species encounter different selection regimes. I hypothesized that species from different pond types would therefore differ in activity behavior, and in plasticity of this behavior. I tested this in a phylogenetic framework to consider the evolution of plasticity in anurans diversifying into different pond types. Time spent active was quantified for larvae of each of 13 anuran species (from three taxonomic families) in four conditions: when no predator was present, and in the non-lethal presence of a dragonfly, newt, or fish predator. Species nested within pond type by taxonomic family differed significantly in time spent active. A significant interaction between predator treatment and taxonomic family was also observed. A phylogenetic analysis of change in behavior revealed strong positive correlations in evolution of these behaviors and suggests constraints on the ability of larval anurans to independently modify activity levels in the presence versus absence of predators.