Effects of a group living experience on the anti-predator responses of individual tadpoles

The tendency to aggregate during the larval stage is widespread and highly variable among anuranspecies. Several studies have highlighted the link between tadpole group density and their activity level,confirming that, usually, living in groups brings several antipredator benefits. However, nearly all studieshave focused on the average behavioural responses of tadpoles tested in groups. In this study, weexplored the effects of living in groups of three different sizes (1, 5 and 25 individuals per group) on theantipredator behaviour of individual green toad,Bufotes balearicus, tadpoles. Wefirst assessed their basalactivity and then examined changes in mobility rate and total distance after exposure to the chemicalcues of predatory dragonfly,Aeshna cyanea, larvae. For both the pre- and poststimulus activity levels, wealso tested the effects of the presence of conspecifics' chemical cues in the experimental tub. Our resultsshowed that (1) a previous brief (8 days) experience of group living is sufficient to affect the basal level ofactivity of individual tadpoles, which increased with group size; (2) tadpoles that were reared alone didnot lower their activity further when exposed to predators' odour; (3) the antipredator response of high-density-reared tadpoles decreased in the presence of conspecifics’cues, supporting the so-called dilutioneffect, which, anyway, may need a minimum group size to be apparent. We conclude that both previousgroup-rearing experience and current perception of the surrounding environment may affect anti-predator behaviour in individual tadpoles.Peer reviewe