Evolution of fitness in the wild

Environments are changing rapidly, which renders many local populations susceptible to extinction unless they can adapt to these changes. Studies of rapid adaptation commonly document the evolution of individual traits. Overall adaptation however, is a function of fitness itself, rather than the individual traits that contribute to fitness. Although numerous studies provide evidence for the evolution of specific traits on contemporary time scales, no published studies of wild animal populations have examined the evolution of a major fitness component following environmental change. My research demonstrates that an introduced population of guppies (Poecilia reticulata) has adapted to its new environment in less than ten years (13-26 generations). This adaptation consists of several phenotypic traits that have changed in the expected direction. Most critically, the introduced population now has higher survival than its ancestral source population when both are tested together in the introduction site. These results show that important components of fitness can evolve rapidly in populations, and that this evolution might influence the persistence of populations in the face of environmental change