Thousands of lakes on coastal lowlands of Cook Inlet, Alaska, contain populations of the threepine stickleback, Gasterosteus aculeatus. Until recession of the last (Naptowne) glacial advance 13,000 years ago, Cook Inlet was filled with glacial ice. As glacial ice withdrew, marine sticklebacks colonized newly-formed freshwater habitats. Marine threespine stickebacks are structurally homogeneous and still occur along the Pacific Cost of North America. Thus, all freshwater sticklebacks in Cook Inlet were derived recently from a known common ancestor. Preliminary studies indicate that Cook Inlet stickleback are structurally diverse, and variable reduction and loss of the pelvic girdle is a common recurrent phenomenon. Recurrent pelvic reduction permits study of interactions of natural selection and intrinsic properties of the organism. Associations between pelvic reduction and environmental variables will be studied using about 300 stickleback populations. The analysis will provide hypotheses for causation of pelvic reduction. Some populations may be too young for extensive pelvic reduction to have evolved. This hypothesis will be tested by analyzing the relation between the extent of pelvic reduction and lake age. The hypothesis that developmental processes bias evolution of vestigial pelvic phenotypes will be tested by studying development of the pelvic girdle in populations without pelvic reduction. Absence of predatory fishes and resultant increased insect predation has already been implicated in evolution of pelvic reduction. Feasibility of testing this hypothesis by studying changes of pelvic phenotype frequencies in lakes with and without introduced predatory fishes will be determined. The proposed research will provide insights into evolutionary mechanisms and form the basis for further evolutionary investigations using pelvic reduction in threepine sticklebacks.
