Patterns of Microsatellite and Mitochondrial DNA Variation Among Anadromous and Freshwater Alewife (\u3cem\u3eAlosa pseudoharengus\u3c/em\u3e) Populations

The spread of exotic species, including the alewife (Alosa pseudoharengus), is quickly becoming one of the greatest threats to the earth\u27s biological diversity. Alewives are native to the western Atlantic seaboard of the United States and Canada. Their life histories include both anadromous and freshwater forms. In the United States, introduced alewife populations have become established in the freshwaters of at least eighteen different states. Recent introductions of alewives into non-native, freshwater habitats have caused much concern because alewives negatively impact a number of other species, particularly salmonids. This thesis examined genetic variation within and among anadromous and freshwater alewife populations. The primary goal was to estimate genetic variation at six microsatellite loci and the mitochondrial DNA (mtDNA) control region in order to clarify biogeography of the alewife. A total of 1062 individuals from 22 populations was examined. The genetic data from these fish were used to investigate hypotheses relating to the origins of alewives it the Finger Lakes of New York and in the North American Great Lakes, as well as four recently introduced alewife populations. This study provided evidence that freshwater alewife populations have significantly lower genetic diversity than anadromous populations for both microsatellite markers and mtDNA. The absence of unique microsatellite alleles and low levels of differentiation in freshwater alewife populations is consistent with the hypothesis that freshwater populations were recently derived from anadromous sources. The genetic data coupled with historical information suggests that the presence of alewives in the Finger Lakes and in the Great Lakes resulted from two independent colonization events and the Finger Lakes of New York were colonized by Hudson River alewives dispersing via the Erie Canal. At least one major reduction in population size (i.e. bottleneck) was associated with this process. In addition, Alewives in Lake Ontario were likely derived by colonization from Hudson River alewives dispersing via canals, although it is possible that the original colonists came from the St.Lawrence River. As with the population in the Finger Lakes, the alewives in Lake Ontario experienced at least one bottleneck. Subsequent colonization of the other Great Lakes from Lake Ontario invovled additional bottlenecks. This study also found that allelic variation at three of the six microsatellite loci (Asa4, Asa9, and Asa12) and mtDNA haplotype variation can be used as diagnostic tools for the identification of anadromous alewives. These markers suggest that alewives from East Grand Lake, Maine, East Twin Lake, Connecticut, and Lake St. Catherine, Vermont are of anadromous origin, while alewives from Northeast Pond, Maine are of freshwater origin