Geographic Patterns in Genetic and Life History Variation in Pumpkinseed Populations from Four East-Central Ontario Watersheds

Abstract

We examined the geographic distribution of biochemical genetic and life history characteristics of 16 populations of pumpkinseed Lepomis gibbosus within four east-central Ontario watersheds to determine (1) if populations within watersheds were more alike for either of these traits than populations among watersheds, (2) if the distribution of genetic and life history characteristics among watersheds coincided with each other, and (3) if the distribution of genetic and life history characteristics among watersheds showed some geographic pattern. Pumpkinseeds collected early in the reproductive season in the years 1990–1993 were assessed for reproductive maturity, gonadosomatic index (females only), and juvenile growth. Allele frequencies at six polymorphic loci were determined by protein electrophoresis. Cluster analysis based upon genetic distance coefficients showed three distinct groups, one containing populations from the Rideau River watershed, a second containing populations from the Crowe River watershed, and a third containing a mixture of populations from the Cataraqui River and Otonabee River watersheds. This cluster pattern does not coincide with a geographic distance matrix among river systems based upon current watersheds, but is consistent with suggested post-Pleistocene recolonization routes from both the Mississippi and Atlantic refugia. Mean age and length at maturity, however, showed an east–west pattern of variation, with the populations in the two central Ontario watersheds maturing earlier and at a smaller size than the populations in the two eastern Ontario watersheds. The cluster pattern of life history traits also did not coincide with a geographic distance matrix based upon current watersheds, nor did it coincide with the cluster pattern based upon genetic distance coefficients. The differences in genetic and life history patterns may reflect original founder effects during initial recolonization events, the effects of drift subsequent to that time, life history responses to east–west differences in natural or human-induced environmental factors, or some combination of these factors. These observed patterns in the distribution of genetic variation (i.e., the clustering of populations within watersheds) support the concept of managing native fisheries by the stock concept.