The Relation Between Demographics and Genetic Integrity of Walleye Sander Vitreus Populations in Northern Wisconsin
Waterhouse, Matthew D.
University of Wisconsin-Stevens Point, College of Natural Resources
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Maintaining genetic integrity is a common objective in the management of both threatened and exploited fish species. A key aspect of genetic integrity is the temporal stability and geographic distribution of genetic diversity. Identifying and understanding the relations between demographics, management activities, and genetic diversity is critical in meeting objectives aimed at conserving genetic integrity. The objectives of this study were to determine if relations exist between the genetic characteristics and demographic variables of northern Wisconsin walleye populations and to determine if walleye growth characteristics were related to genetic or demographic variables in northern Wisconsin walleye. A set of 10 microsatellite loci were used to determine the genetic characteristics of 15 walleye populations by calculating expected heterozygosity (He), effective number of alleles (Ae), allelic richness (Ar), the inbreeding coefficient (FIS), individual-specific internal genetic distance measure (mean d^2), mean relatedness (r), and pairwise estimates of genetic distance between populations (φ-st). Long-term monitoring data (1990- 2009) from the Wisconsin Department of Natural Resources and Great Lakes Indian Fish and Wildlife Commission were used to calculate demographic variables including sex ratio, lake surface area (proxy of total abundance), recruitment (YOY), and stocking intensity. Dorsal spine samples were used to determine age and early growth characteristics of each population. Relative condition factor (Kn) was used to measure the mean condition of fish in each population. Simple linear and forward stepwise regression modeling was used to determine the relation between each genetic characteristic and demographic variable. The results of this study showed significant relations between genetic and demographic characteristics of walleye populations. Genetic characteristics were strongly related to demographic variables; for example, YOY and age predicted over 70% of the variance in inbreeding FIS estimates (df = 12, F = 18.403, p < 0.001). An observed skew in the sex ratio correlated to decreased effective population size. This likely resulted in increased rates of genetic drift and subsequently, the observed lower genetic diversity measures. The genetic drift may have further impacted the population as demonstrated by a decrease in age-1 length in populations with lower levels of genetic diversity (df = 13, F = 6.109, p = 0.028). Stocking had significant impacts on both intra- and inter-population genetic diversity. Stocked populations had significantly higher levels of genetic diversity relative to non-stocked populations consistent with relations between stocking intensity and both He and Ae. Stocking also correlated to an observed disruption in the pattern of interpopulational genetic diversity. A Mantel test showed a significant interaction between geographic distance and genetic differentiation in non-stocked populations (1,000 permutations, Z = 5,154.65, p = 0.019) but no pattern was observed in stocked populations (1,000 permutations, Z = 1,117.89, p = 0.068) indicating stocking may disrupt the natural distribution of genetic diversity among walleye populations (genetic structure). Overall, results showed significant influences of demographics on the genetic integrity of walleye in Wisconsin. Low levels of recruitment, highly skewed sex ratio, and stocking intensity appeared to pose threats to the genetic integrity of walleye and should be considered in management programs aimed at conserving the genetic integrity of naturally recruiting populations.