Population Structure as Revealed by mtDNA and Microsatellites in Northern Fur Seals, Callorhinus ursinus, throughout Their Range

Background: The northern fur seal (Callorhinus ursinus; NFS) is a widely distributed pinniped that has been shown to exhibit a high degree of philopatry to islands, breeding areas on an island, and even to specific segments of breeding areas. This level of philopatry could conceivably lead to highly genetically divergent populations. However, northern fur seals have the potential for dispersal across large distances and have experienced repeated rapid population expansions following glacial retreat and the more recent cessation of intensive harvest pressure. Methodology/Principal Findings: Using microsatellite and mitochondrial loci, we examined population structure in NFS throughout their range. We found only weak population genetic structure among breeding islands including significant FST and W ST values between eastern and western Pacific islands. Conclusions: We conclude that insufficient time since rapid population expansion events (both post glacial and following the cessation of intense harvest pressure) mixed with low levels of contemporary migration have resulted in an absence of genetic structure across the entire northern fur seal range

Bayesian skyline plot of historical female effective population size, light lines represent the 95% highest posterior probability density around the estimate.

<p>Bayesian skyline plot of historical female effective population size, light lines represent the 95% highest posterior probability density around the estimate.</p

Summary of mtDNA diversity in 9 populations of Northern fur seal.

<p>*haplotypic diversity (h), % nucleotide diversity (Π). Standard deviations in parentheses.</p

Distribution of northern fur seal breeding sites.

<p>Distribution of northern fur seal breeding sites.</p

Minimum spanning network of 112 core mitochondrial DNA haplotypes of northern fur seals.

<p>Branch lengths are the minimum number of steps between haplotypes. The size of the circle representing the individual haplotypes corresponds to the abundance of that haplotype. Numbers identify the most abundant haplotypes. Dashed lines represent alternative groupings.</p

Mitochondrial DNA based population differentiation for population pairs (estimates of F_ST above diagonal and Φ_ST below diagonal).

<p>*Bold indicates significant <i>P</i>-values (<i>P</i><0.05).</p

The observed pairwise mismatch distribution of mtDNA in northern fur seals as compared to the expected distribution based upon a model of sudden population expansion.

<p>The observed pairwise mismatch distribution of mtDNA in northern fur seals as compared to the expected distribution based upon a model of sudden population expansion.</p

Isolation by distance based on mitochondrial DNA analysis in northern fur seals including the relationship between genetic distance, pairwise comparisons of rookeries (Φ_ST ) and the natural log of the geographic distance between the rookery pairs.

<p>Isolation by distance based on mitochondrial DNA analysis in northern fur seals including the relationship between genetic distance, pairwise comparisons of rookeries (Φ_ST ) and the natural log of the geographic distance between the rookery pairs.</p