Microsatellite and mitochondrial DNA markers show no evidence of population structure in walleye (Sander vitreus) in Lake Winnipeg

Abstract

Walleye (Sander vitreus) are the main contributor to Manitoba's multi-million dollar commercial fishery, with Lake Winnipeg providing the largest and most profitable catch. In some systems, walleye show evidence of returning to the same spawning site each spring (i.e., philopatry), which can lead to the existence of multiple genetically-discrete spawning groups (i.e., stocks) within a lake. This study used nine microsatellite loci (N=932) and one mitochondrial restriction fragment length polymorphism assay (N=123) to investigate possible genetic divergence among walleye from 13 spawning sites in Lake Winnipeg, and compared these with those collected from two hatchery locations and other locations outside of Lake Winnipeg. Microsatellite loci resolved little population structure within Lake Winnipeg, with the exception of two sites (Grand Rapids and the Icelandic River), which showed low but significant levels of genetic divergence with most other sites (Fst=0.0066–0.0457). Slight to moderate genetic divergence was found between Lake Winnipeg walleye and sampling locations outside of Lake Winnipeg (Fst=0.0037–0.1054, P=0.0002). Mitochondrial DNA analysis indicated colonization of Lake Winnipeg by walleye from two glacial refugia (Missourian and Mississippian), but no population structure was detected among sites. The lack of stock structure found in Lake Winnipeg possibly indicates a low degree of natal philopatry, an amount of straying sufficient to obscure genetic structure, or obscured structure as a result of historical and current stocking. Overall genetic variation, using both mitochondrial and microsatellite markers, appeared comparable to that found in other walleye populations.