PHENOTYPIC PLASTICITY IN THE LIFE HISTORY TRAITS OF GUPPIES: RESPONSES TO SOCIAL ENVIRONMENT

Abstract

Guppies (Poecilia reticulata) living in the streams and rivers of Trinidad show significant interpopulation variation in life history traits. Some of the greatest divergence is among guppies that co-occur with different assemblages of predators. Reznick has demonstrated that there is a genetic basis for some, but not all, of these differences. Several features of guppies’ biology co-vary with the predatornities including their social and sexual behaviors and the demography of their populations. Here, we test the hypothesis that some of the observed phenotypic variation in life history traits is induced by differences in the social environment of guppies. We tested this by rearing focal individuals in the laboratory in experimental populations composed of wild-caught guppies. The experimental populations were designed to represent two types of guppy communities: (1) Rivulus communities, where guppies co-occur only with a small killifish, Rivulus hartii, that preys on small guppies, and (2) Crenicichla communities, where they co-occur with several larger species of predator including Crenicichla alta, a cichlid that prefers to prey on large guppies. We manipulated both the demography and the origin (predator community) of the guppies comprising the experimental populations. The focal guppies were offspring of guppies from one of the two predator localities. We found that guppies responded to both the demography and origin of the conspecifics with which they were reared. Therefore, phenotypic plasticity in response to social environment is probably contributing to the variation in life history traits that has been observed in the field. Our discovery that there are differences in the responsiveness of guppies from Rivulus and Crenicichla localities to our manipulations of social environment suggests that the patterns of plasticity have themselves evolved.