Patterns of extensive genetic differentiation and variation among European harbor seals (Phoca vitulina vitulina) revealed using microsatellite DNA polymorphisms

Abstract

The harbor seal (Phoca vitulina) has the most extensive distribution of any phocid seal species. An analysis of population structure in this species across its European range was made using 7 phocid derived microsatellites in a sample of 1,029 individuals from 12 separate geographic areas. Despite the species potential for long-distance movement, significant genetic differentiation between areas was observed using an unbiased estimator of RST. Six distinct population units were identified: Ireland-Scotland, English east coast, Waddensea, western Scandinavia (Norway-Kattegat-Skagerrak-west Baltic), east Baltic, and Iceland. Little local substructuring is present along coastlines with a continuous distribution of breeding animals, but differentiation does increase with geographic distance. The degree of differentiation is greater over equivalent distances where the distribution is discontinuous, such as along coasts where breeding colonies are separated by large distances or by stretches of open sea. Patterns of population differentiation derived from microsatellites are very similar to those obtained from previous mitochondrial DNA analysis and suggest that philopatry in harbor seals operates over 300-500 km. In Europe, harbor seals have experienced a complex demographic history and patterns of population structure are likely to have been affected by natural environmental influences such as Pleistocene glaciations and epizootics. Comparison of Nm values from an unbiased estimator of RST, GST, and theta are consistent and, in some cases, may indicate populations where conditions deviate from the expectations of the RST model.

Genomic signatures of population bottleneck and recovery in Northwest Atlantic pinnipeds

“…The differences may also be due to the wider geographic range sampled for gray seals in comparison with harbor seals, but our findings of no significant structure or differences in diversity between gray seal colonies do not strongly support this potential explanation. Although differences in species diversity have not been previously observed in microsatellite markers assessed in both species (Goodman, 1998; Worthington Wilmer et al., 1999), one study of genetic diversity at the immune gene complex, MHC class I, in gray and harbor seals reports preliminary findings of greater diversity in gray seals in a small number of individuals (Hammond, Guethlein, Norman, & Parham, 2012). If harbor seals are truly less genetically diverse than gray seals at immune markers and/or more broadly across the genome, this may, in part, explain general observations of lower disease resistance among harbor seals than gray seals (Bogomolni, 2014), an avenue of research that requires further investigation of diversity in functional regions of the genome at a population or species‐wide scale.…”

“…In comparison with the relatively rich history of regional genetic studies of gray seals (Allen, Amos, Pomeroy, & Twiss, 1995; Cammen, Hoffman, Knapp, Harwood, & Amos, 2011; Gaggiotti et al., 2002) and to a slightly lesser extent harbor seals (Goodman, 1998; Olsen et al., 2017) in the Northeast Atlantic, there exists relatively little parallel analysis of gray or harbor seals in the Northwest Atlantic, and few attempts to model or monitor long‐ or short‐term histories using genetic tools. Samples from this region have been occasionally incorporated into worldwide or ocean basin analyses (Cammen et al., 2011; Klimova et al., 2014; Stanley et al., 1996), but within the Northwest Atlantic, most seal genetics studies have focused on a single colony (Coltman, Bowen, & Wright, 1998; Worthington Wilmer, Allen, Pomeroy, Twiss, & Amos, 1999).…”

Heterozygosity and lungworm burden in harbour seals (Phoca vitulina)

“…It is known that harbour seals exhibit strong population substructure, with significant genetic differences between populations that are easily within the reach of dispersing youngsters (Goodman, 1998). Such structure has the potential to allow or even promote some level of inbreeding.…”

“…We considered 94 published pinniped microsatellite primers (Allen, 1995;Allen et al, 1995;Coltman et al, 1996;Gemmell et al, 1997;Goodman, 1997Goodman, , 1998Buchanan et al, 1998;Davis et al, 2002;HernandezVelaquez et al, 2005;Hayes et al, 2006;Hoffman et al, 2006;Wolf et al, 2006). Of these, 38 had previously been tested on four harbour seals from Scotland and were dismissed because they were either monomorphic or failed to amplify.…”

“…b In harbour seals of the North Sea (Goodman, 1998). c In harbour seals of the Western Wadden Sea (Goodman, 1998).…”