Inter- and intraspecific trait compensation of defence mechanisms in freshwater snails

Trait compensation occurs when mechanically independent adaptations are neg atively correlated. Here, we report the first study to demonstrate trait co mpensation in predator-defence adaptations across several species. Freshwat er pulmonate snails exposed experimentally to predation chemical cues from fishes and crushed conspecifics showed clear interspecific differences in t heir behavioural avoidance responses, which were negatively correlated with shell crush resistance. The type of avoidance response varied between spec ies. thin-shelled species (Lymnaea stagnalis and Physa fontinalis) moved to the Mater-line or out of the water: while those with thick shells moved un der cover or showed a mixed response. There were also intraspecific size-li nked differences, with an ontogenetic increase in shell strength accompanie d by a decrease in behavioural avoidance. Such trait compensation in respon se to predation has important implications for interspecific interactions a nd food-web dynamics.