The demographic history and population structure of three species of wolffishes across the North Atlantic Ocean

This thesis comprises five research chapters, one consisting of a review and meta-analysis of published information on genetic variation in fishes, and four describing new research on genetic variation in wolffishes. The principal finding from the review chapter was that both mtDNA and microsatellite diversity in fishes were correlated with abundance, as measured by global catch statistics, consistent with the prediction based on the theory of selective neutrality. Various factors, such as sample size, number of loci, and particular mtDNA region assessed, influenced the strength of correlations in predictable ways. The main goal of the thesis was to assess genetic variation in three species of wolffishes that are of conservation concern in Canadian waters. To this end, mitochondrial DNA, microsatellite, and amplified fragment length polymorphism markers were assessed in order to determine phylogeographic patterns, historical demography, and population structure in Atlantic (Anarhichas lupus Linnaeus 1758), spotted (A. minor Olafsen 1772), and northern (A. denticulatus Kroyer 1845) wolffishes.;Phylogeographic divergence across the range for all three species was low and estimated divergence times were broadly consistent with post-glacial colonization of the range from a single refuge from the eastern Atlantic Ocean. However, this inference was dependent on accurate mutation rate estimates, which remain uncertain. Atlantic wolffish exhibit significant population structure across the range, as revealed by microsatellite variation, defined by the presence of four distinct groups: two within Atlantic Canada, one across the North Atlantic, and Rockall Bank. Range-wide FST values were low (<≤0.035), despite life history attributes such as large benthic eggs, large larvae, a limited pelagic stage, and relatively sedentary adults that suggested potential for strong population structure. Population structure in northern wolffish was characterized by significant genetic differentiation between the Barents Sea samples versus the rest of the range, and population structure in spotted wolffish was weak overall, possibly related to the low diversity of marker loci. All three species, but northern and spotted wolffishes in particular, were characterized by low microsatellite diversity indicating low long-term effective population sizes. Results suggest that northern and spotted wolffishes could be at risk of reduced fitness due to inbreeding and reduced adaptive potential.