Population and Fishery Genetics of Walleye
Walleye: We have developed a baseline data set for variation among 15 microsatellite loci for walleye across Lake Erie and the Great Lakes. To date 2217 walleye have been analyzed, including 1859 from the Great Lakes and 1607 from Lake Erie.
Carol A. Stepien, Douglas J . Murphy, Rachel N. Lohner, Osvaldo J. Sepulveda-Villet, and Amanda E. Haponski
Molecular Ecology (2009) volume 18, pages 3411-3428
Abstract: Population genetic relationships reveal the signatures of current processes such as reproductive behaviour and migration, as well as historic events including vicariance and climate change. We analyse population structure of native walleye Sander vitreus across North America, encompassing 10 nuclear DNA microsatellite loci, 26 spawning sites and 921 samples from watersheds across the Great Lakes, Lake Winnipeg, upper Mississippi River, Ohio River and Mobile Bay of the Gulf Coast. Geographical patterning is assessed using phylogenetic trees, pairwise FST analogues, hierarchical partitioning, Mantel regression, Bayesian assignment and Monmonier geographical networks. Results reveal congruent divergences among population groups, corresponding to historic isolation in glacial refugia, dispersal patterns and basin divisions. Broad-scale relationships show genetic isolation with geographical distance, but reproductive groups within basins do not – with some having pronounced differences. Greatest divergence distinguishes outlying Gulf Coastal and northwest populations, the latter tracing to dispersal from the Missourian refugium to former glacial Lake Agassiz, and basin isolation ~7000 ya. Genetic barriers in the Great Lakes separate groups in Lakes Superior, Huron’s Georgian Bay, Erie and Ontario, reflecting contributions from Mississippian and Atlantic refugia, and changes in connectivity patterns. Walleye genetic patterns thus reflect vicariance among watersheds and glacial refugia, followed by re-colonization pathways and changing drainage connections that established modern-day northern populations, whose separations are maintained through spawning site fidelity. Conservation management practices should preserve genetic identity and unique characters among these divergent walleye populations.
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Figure 1. Map showing locations of collection sites for walleye, with primary sampling sites lettered. Dotted line encircles the Great Lakes watershed, dashed line designates maximal extent of the Wisconsin glaciations and arrows denote hypothesized colonization pathways from glacial refugia (adapted from Murdoch & Hebert 1997; Mandrak & Crossman 1992). Roman numerals show the 10 primary genetic divisions among populations based on our results using the Manni et al. (2004a,b) BARRIER approach, designated with Roman numerals ranked from the greatest to less pronounced (I to X; % Bootstrap support and number of loci supporting each barrier are given in Results). Colours of dots correspond to primary population group membership representation according to Bayesian STRUCTURE analysis (Pritchard et al. 2000; Pritchard & Wen 2004) detailed in Fig. 3.
Figure 2. Pairwise relationship between genetic distance (θST ⁄ 1 – θST) vs. the natural logarithm of geographical distance (km) across all population samples (A–Q) P < 0.0001**, R2 = 0.263, r = 0.513, y = 0.043x + 0.180.
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Figure 3. Estimated population structure of walleye from Bayesian STRUCTURE analysis (Pritchard et al. 2000; Pritchard & Wen 2004) for K = 4, 6 and 9 population groups. K = 4 and 6 had the highest ΔK vs. K peak height (Evanno et al. 2005), and K = 9 had the highest posterior probability value (0.998; Pritchard et al. 2000). Each individual is represented by a thin vertical line, which is partitioned into K colored segments that represent its estimated population group membership fractions. Black lines separate individuals from spawning site locations (labeled above), whose geographical regions are labeled below (following Fig. 1).