Phenotypic Variation in Threespine Sticklebacks (Gasterosteus aculeatus) of the Chignik River System, Alaska

Abstract

Four phenotypes of the threespine stickleback, Gasterosteus aculeatus Linnaeus, were identified from the two Chignik lakes, Alaska: unplated (2–6 anterior plates); half-plated (7–15 anterior plates); fully plated (18–22 plates) lacustrine; and fully plated (18–22) estuarine. Distinctions lie in number and size of lateral plates and extent of lateral keel development on the caudal peduncle. Composition of the three lacustrine phenotypes in either lake population was similar among the years 1962–64 for both age I and age II in Black Lake but dissimilar in Chignik Lake. The Black Lake population contained a higher proportion of the unplated and half-plated phenotypes but fewer of the fully plated phenotypes than the Chignik Lake population. The life history of the estuarine phenotype is outlined. The mechanisms responsible for the maintenance of the four phenotypes in the Chignik River system have not been determined.