MITOCHONDRIAL-DNA DIVERSITY OF BROWN BULLHEAD FROM CONTAMINATED AND RELATIVELY PRISTINE SITES IN THE GREAT-LAKES

Brown bullhead were sampled from contaminated and relatively pristine sites to determine whether there was any association between genetic d iversity and site contamination. Nine sites were sampled in the lower Great Lakes: five from Areas of Concern (identified by the Internation al Joint Commission as having significant environmental degradation) a nd four from relatively clean areas of similar habitat type. Genetic v ariation was surveyed in the mitochondrial genome using restriction fr agment length polymorphisms. Sixteen restriction enzymes were used to identify 42 distinct mitochondrial. DNA haplotypes among 163 fish. Eig ht pairwise comparisons of populations at contaminated vs. clean sites showed that genetic diversity estimates were always lower in populati ons from contaminated sites. The most parsimonious explanation is that reduced diversity is a result of stochastic reductions in population size that have culled much of the genetic diversity from populations. Although contaminated sites support large populations of brown bullhea d, historical environmental degradation at these sites may have reduce d population size in the past, resulting in reduced present-day geneti c diversity.