Genetic studies: Across the Great Lakes - Across Lake Erie
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 1715 walleye have been analyzed, including 1381 from the Great Lakes and 1192 from Lake Erie.
Landscape genetic patterning of Walleye Sander vitreus: Vicariance, postglacial dispersal and spawning philopatry
Carol A. Stepien, Rachel N. Lohner, and Douglas J. Murphy
Abstract: Population genetic relationships reveal the signatures of current processes such as reproductive behavior and migration, as well as historic events including vicariance and climate change. We employ a landscape genetics approach to analyze these patterns among native walleye Sander vitreus populations across North America; including 10 nuclear DNA microsatellite loci, 26 spawning sites, and 972 samples from watersheds across the Great Lakes, Lake Winnipeg, upper Mississippi River, Ohio River, and Mobile Bay. Geographic patterning is assessed using phylogenetic trees, pairwise FST analogs, AMOVA partitioning, Mantel regression, Bayesian assignment, 3-d factorial correspondence, and Monmonier geographic networks. Results reveal marked differences among populations, corresponding to historic isolation in glacial refugia and watershed divisions. The greatest landscape genetic division distinguishes populations from Lake Winnipeg and northwest Ontario lakes from those in the upper Great Lakes, with the former sharing presumed origins from a Missourian glacial refugium. The next two divisions further partition those populations, and the fourth isolates a historic relict population from the Tombigbee River watershed that drains into the Gulf Coast’s Mobile Bay. Other significant genetic barriers occur within the Great Lakes, separating populations in Lake Superior, Lake Huron’s Georgian Bay, the upper from the lower Great Lakes below Lake St. Clair, and Lake Ontario. The final barrier links walleye from the Ohio River watershed with those from Lake Oneida, separating that group from the Great Lakes watershed. Landscape genetic patterns thus show patterns of vicariance among watersheds and glacial refugia, followed by recolonization pathways that established modern-day northern populations and likely maintained separations through spawning site fidelity. Conservation management practices should preserve genetic identity and unique characters among these markedly divergent walleye populations.
Figure 1. Pairwise relationship between genetic distance (ӨST/1-ӨST) versus the natural logarithm of geographical distance (km). P = 0.0001**, R2 = 0.2628, y = 0.0431x - 0.1798.
Figure 2. Neighbor-joining tree (Saitou and Nei 1978; constructed in PHYLIP) showing relationships among major population areas for walleye based on Nei’s (1972) genetic distances. The tree calculated from Cavalli-Sforza and Edwards’ (1967) chord distances was similar in topology and resolution, and is thus not shown. Tree is “rooted” with its sister species, the sauger S. candense. Values at nodes denote relative percent support from 1000 bootstrap iterations.
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Figure 3. Estimated population structure for walleye from STRUCTURE analysis for K= 9 groups (with the latter number having the greatest mean likelihood values). Each individual is represented by a thin vertical line, which is partitioned into K colored segments that represent the individual’s estimated membership fractions. Black lines separate individuals from different spawning sites, which are labeled below the figure. Ten STRUCTURE runs at K = 9 produced nearly identical individual membership coefficients, having pairwise similarity coefficients above 0.95, and the figure illustrating a given K is based on the highest probability run at that K. Posterior probability = 0.998.
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Figure 4. Map showing the nine primary genetic break divisions (red lines) among walleye populations using the Manni et al. (2004a,b) BARRIER approach, designated with Roman numerals from greatest to less pronounced (I to IX). Letters designate locations of collection sites for walleye, with further information in Table 1. Dotted line encircles Great Lakes watershed. Dashed line indicates Wisconsinian Glacial Maximum.
Genetic studies: Across the Great Lakes - Across Lake Erie
