Heritable intraspecific variation among prey in size and movement interact to shape predation risk and potential natural selection

Abstract

AbstractPredator and prey traits are important determinants of the outcomes of trophic interactions. In turn, the outcomes of trophic interactions shape the evolution of predator and prey traits. How species’ traits are likely to respond to selection from trophic interactions depends crucially on whether and how heritable species’ traits are and their genetic correlations. Of the many traits potentially influencing the outcomes of trophic interactions, body size and movement traits have emerged as universally key traits. Yet, how these traits shape and are shaped by trophic interactions is generally unclear, as few studies have simultaneously measured the impacts of these traits on the outcomes of trophic interactions, their heritability, and their correlations within the same system.We used outcrossed and then clonally propagated lines of the ciliate protistParamecium caudatumfrom natural populations to examine variation in morphology and movement behavior, the extent to which this variation was heritable, and how intraspecific differences among lines alteredParameciumsusceptibility to predation by the copepodMacrocyclops albidus.We found that theParameciumlines exhibited heritable variation in body size and movement traits. In contrast to expectations from interspecific allometric relationships, body size and movement speed showed little covariance among clonal lines. The proportion ofParameciumconsumed by copepods was positively associated withParameciumbody size and velocity, however, we also found evidence of an interaction such that greater velocities led to greater predation risk for large body-sized paramecia but did not alter predation risk for smaller body-sized paramecia. The proportion of paramecia consumed was not related to copepod body size. These patterns of predation risk and heritable trait variation in paramecia suggest that copepod predation may act as a selective force operating independently on movement and body size and generating the strongest selection against large, high-velocity paramecia.Our results illustrate how the interactions between ecology and genetics can shape the potential natural selection on prey traits through the outcomes of trophic interactions. Further simultaneous measures of predation outcomes, traits, and their quantitative genetic characteristics will provide insights into the evolutionary ecology of species interactions and their eco-evolutionary consequences.