The Relation Between Demographics and Genetic Integrity of Walleye Sander Vitreus Populations in Northern Wisconsin
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Date
2011-11Author
Waterhouse, Matthew D.
Publisher
University of Wisconsin-Stevens Point, College of Natural Resources
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Show full item recordAbstract
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.