Population genetic structure, phylogeography and spawning philopatry in walleye (Stizostedion vitreum) from mitochondrial DNA control region sequences

Mitochondrial (mt) DNA control region sequences were used to test the genet ic and phylogeographic structure of walleye Stizostedion vitreum population s at different geographical scales: among spawning sites, fake basins, lake s, and putative glacial refugia in the Great Lakes region. Sequencing 199 w alleye revealed nucleotide substitutions and tandemly repeated sequences th at varied in copy number, as well as in sequence composition, in approximat e to 1200 bp of the mtDNA control region. Variable numbers of copies of an 11-bp tandem repeat showed no geographical patterning and were not used in further analyses. Substitutions in the other areas of the control region yi elded 19 haplotypes, revealing phylogeographic structure and significant di fferences among glacial refugia, lakes, basins and some spawning sites. Dif ferences among spawning populations were consistent with reduced gene flow, philopatry and possible natal homing. Analysis of spawning populations sho wed consistency of genotypic frequencies among years and between males and females, supporting philopatry in both sexes. The unglaciated plateau in so uthern Ohio, USA housed a very different haplotype that diverged prior to t he Missouri, Mississippi and Atlantic glacial refugia types. Haplotypes fro m the three refugia colonized the Great Lakes after retreat of the Wisconsi n glaciers, and their present distribution reflects the geography of their prior isolation and differential colonization. Populations that became asso ciated with spawning localities appear to have diverged further due to phil opatry, resulting in fine-scale phylogeographic structuring.