Evidence of a Genetic Basis for Absence of the Pelvic Skeleton in Brook Stickleback, Culaea inconstans, and Notes on the Geographical Distribution and Origin of the Loss

Abstract

Laboratory and field crosses show that the absence of the pelvic skeleton in a brook stickleback population is under partial genetic control. Some offspring of parents lacking the pelvis possess a complete pelvic skeleton, while some offspring of parents with a complete pelvic skeleton lack the pelvis. Although a wide range of morphologically intermediate states exists, intermediates do not predominate in the crosses.Loss of the pelvic skeleton occurs in Ontario, Saskatchewan, and Alberta. Within Alberta, 23 localities are known where 20% or more of the sticklebacks lack a complete pelvic skeleton. In some localities 95% or more of the individuals lack all trace of the pelvis. Variation in predation is inferred to be the environmental variable causally associated with the presence or absence of the pelvic skeleton. The absence is postulated to have arisen independently in the various localities. Key words: Culaea inconstans, brook stickleback, pelvic skeleton absence, genetic control.