Isolating Confounding Abiotic and Biotic Effects on the Phenotype on Physa Acuta Snails

Abstract

Organisms match their phenotypes to prevailing environmental conditions leading to habitat specific polymorphisms. Polymorphisms arise from genetic divergence, phenotypic plasticity, or a combination of both processes. I examined the presence of habitat-specific polymorphism in Physa acuta snails collected from three streams and their corresponding downstream reservoir. In lotic systems shells were rotund with larger apertures, while those from lentic systems were more elongate with smaller apertures. In a reciprocal transplant lab experiment that crossed flow regime and crayfish predator cues, I tested for the underlying mechanisms responsible for the observed phenotypic differences. I found no evidence for plasticity in relation to flow regime. However, there was a habitat-specific plastic response to crayfish predator cues. Snails experiencing crayfish cues that originated from the pond became more elongate, while snails from the stream became more globose. Shell shape differences arising from flow regime are likely genetic, while those from predator cues seem to be plastic. Most importantly, the nature of shape change in response to predator cues depended on flow regime. These results add to a growing body of literature on the importance of abiotic factors that influence how organisms respond to biotic factors