Mitochondrial DNA Variation and Stock Structure of Walleyes from Eastern Lake Huron: An Analysis of Contemporary and Historical Samples

Abstract

The spatial and temporal distributions of mitochondrial DNA (mtDNA) haplotypes in walleyes Stizostedion vitreum captured from spawning stocks were examined to assess genetic population structure in eastern Lake Huron, Ontario. We also assessed mtDNA variation in pond-reared fish relative to that in their parental sources to determine whether cultured fish have the potential to influence mtDNA structure within and among stocks. Restriction fragment length polymorphisms in two polymerase-chain-reaction-amplified fragments totaling 7.6 kilobases and sequencing 310 base pairs of the control region were used to assess mtDNA variation in both archived scales and contemporary samples collected from 1965 to 1998. Although many stocks in eastern Lake Huron differed significantly in pairwise comparisons of contemporary haplotype frequencies, fish from eastern Georgian Bay and the French River complex exhibited low mtDNA differentiation. Low nucleon diversity (h) and the absence of low-frequency haplotypes (<0.15) were observed in some stocks, particularly those examined in eastern Georgian Bay. There appeared to be a loss of mtDNA variation in two stocks, which exhibited a general reduction in h, loss of low-frequency haplotypes, and a significant change in haplotype frequencies over a 28-year and a 33-year period, respectively. Cultured walleyes from rearing ponds had reduced h, lower numbers of haplotypes, and significantly different haplotype frequencies compared with their parental sources.