Because of its amenability to experimental manipulation, and the availability of methodologies for genetic analysis, the microcrustacean complex Daphnia pulex provides an outstanding model system for the study of the interfaces between population genetics, mating systems, molecular evolution, and ecology. The proposed work is concerned particularly with the mechanisms that constrain the tempo and mode of microevolutionary change. Each form of reproduction is thought to have unique advantages and disadvantages. For example, species which reproduce by parental gene exchange generate variable phenotypes each generation. These species can be adaptive in variable environments, but they suffer from inbreeding depression, a significant problem in colonizing environments. Species which reproduce without parental gene exchange are believed to be ideal colonizers, but they appear in some cases to be lacking in evolutionary flexibility and to be doomed to rapid extinction due to the rapid build-up of mutational load. Unfortunately, there are few good empirical data on any of these matters. The proposed work will quantify these types of tradeoffs to gain insight into the mechanisms of evolutionary change at the molecular and phenotypic levels. Results should have broad implications for a number of problems in applied biology including plant and animal breeding, pest and disease organisms, and the extinction process.
