PELVIC REDUCTION IN THREESPINE STICKLEBACK FROM COOK INLET LAKES - G GEOGRAPHICAL-DISTRIBUTION AND INTRAPOPULATION VARIATION

Loss of one or more elements of the pelvic complex occurs at substanti al frequencies (greater-than-or-equal-to 5%) in 55 and at lower freque ncies in 42 of 204 populations of Gasterosteus aculeatus sampled from freshwater sites around Cook Inlet, Alaska. Populations with substanti al pelvic reduction are widely distributed and interspersed among thos e lacking it. Intrapopulation phenotype frequencies vary greatly withi n limited areas but may be similar in distant populations. Intrapopula tion phenotype frequency distributions include bimodal, flat, normal, skewed, and truncated; and their form may vary among adjacent populati ons. High intrapopulation frequencies of pelvic reduction apparently h ave evolved repeatedly within Cook Inlet, but gene flow is probably im portant in spreading genetic variation for pelvic reduction among popu lations. Divergent populations of Cook Inlet threespine stickleback sh ould be treated as parts of an endemic radiation, which warrants speci al consideration for conservation as a unit.