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

The genetic legacy of extreme exploitation in a polar vertebrate

Understanding the effects of human exploitation on the genetic composition of wild populations is important for predicting species persistence and adaptive potential. We therefore investigated the genetic legacy of large-scale commercial harvesting by reconstructing, on a global scale, the recent demographic history of the Antarctic fur seal (Arctocephalus gazella), a species that was hunted to the brink of extinction by 18th and 19th century sealers. Molecular genetic data from over 2,000 individuals sampled from all eight major breeding locations across the species’ circumpolar geographic distribution, show that at least four relict populations around Antarctica survived commercial hunting. Coalescent simulations suggest that all of these populations experienced severe bottlenecks down to effective population sizes of around 150–200. Nevertheless, comparably high levels of neutral genetic variability were retained as these declines are unlikely to have been strong enough to deplete allelic richness by more than around 15%. These findings suggest that even dramatic short-term declines need not necessarily result in major losses of diversity, and explain the apparent contradiction between the high genetic diversity of this species and its extreme exploitation history

Phylogenetic relationships, population genetics and hybridisation of two species of southern fur seal (Arctocephalus spp.)

This research investigated the phylogenetic relationships and population genetics of two species of fur seal in order to provide a basis for the study of the hybridisation of these species at Macquarie Island. The Antarctic (Arctocephalus gaze/la) and subantarctic fur seals (Arctocepha/us tropicalis) occur throughout the subantarctic region of the Southern Ocean, hauling out on remote islands throughout the region to breed. Both species were subject to intense sealing activities in the 18th and 19th centuries. The competitive and indiscriminate nature of the industry ensured that all populations were greatly reduced in size, with some becoming extinct. The cessation of sealing in the early 20th century has allowed both species to recover in number, and recolonise islands across their former range. The current range for the Antarctic fur seal overlaps with that of the subantarctic fur seal at lies Crozet, Marion Island and Macquarie Island. Hybridisation has been reported at low levels at Marion Island, and at higher levels at Macquarie Island. The situation at Macquarie Island is further complicated by the presence of an additional species, the New Zealand fur seal (Arctocephalus forsteri) While this species is not breeding on the island, some males participate in the breeding process, with some hybrids being produced This research seeks to apply molecular methods to investigate the hybridisation that is occurring at Macquarie Island within the context of the evolutionary and recent history of the two breeding fur seal species, and to a lesser extent, the New Zealand fur seal. The phylogenetic relationships of the Antarctic and subantarctic fur seals were investigated within the context of the family Otariidae. This family include the nine species of fur seal (Genera Arctocephalus and Callorhinus), and five species of sea lion (Genera Neophoca, Phocarctos, Eumetopias, Zalophus, and Otaria). A 360 base pair region of the cytochrome b gene in the maternally inherited mitochondrial genome was used for the primary phylogenetic analysis of the family, while a 356 base pair fragment of the mitochondrial control region was used to enhance resolution of the terminal nodes. The traditional classification of the family into the two. subfamilies Arctocephalinae (fur seals) and Otariinae (sea lioris) was not supported, as the fur seal Cal/orhinus ursinus was found to be basal to all other fur seal and sea lion taxa. While four sea lion clades and five fur seal clades were consistently observed through all analyses conducted, it was not possible to adequately resolve the relationships among these clades. This probably reflects the rapid radiation of these taxa that occurred about 3 million years ago. The subantarctic fur seal was found to be most closely related to the Australian and Cape fur seals (A. pusillus) while the closest species related to the Antarctic fur seal was not clearly resolved. However, there were discrete species specific differences observed between the Antarctic, subantarctic and New Zealand fur seals in both the cytochrome b gene and the control region, providing the basis for species identification within the hybridising population at Macquarie Island. The investigation into the level and distribution of genetic variation in the Antarctic and subantarctic fur seals was conducted using two classes of molecular marker. The mitochondrial control region is a commonly used marker for investigation into population genetics issues, due in part to the relatively high rate of mutation. Microsatellites are highly variable regions within the nuclear genome, and with a bi-parental mode of inheritance, provide a natural complement to the maternally inherited mitochondrial genes. Given that historic records indicate both fur seal species had passed through population bottlenecks as a result of sealing, it was suspected that the current level of genetic variation may be low. This is because reduced levels of variation have been observed in other species that have passed through extreme population bottlenecks at some stage in the recent past (eg. the northern elephant seal, Mirounga angustirostris). Surprisingly, the nucleotide diversities of the Antarctic and subantarctic fur seals, as determined by the mitochondrial control region, were found to be high (3.2% and 4.8% respectively). The level of genetic variation as exhibited by the 10 microsatellite loci was generally high (overall heterozygosity levels 0.54-0.62 for the three species), though variable between loci. Despite the overlapping allele size ranges for most of the loci, significant allelic and genotypic differentiation was observed between the three species (P < 0.000). Significant population structure was evident within the subantarctic fur seal with both the mitochondrial

Predation by Hooker's sea lion (Phocarctos hookeri) on a small population of fur seals (Arctocephalus spp.) at Macquarie Island

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Post-sealing genetic variation and population structure of two species of fur seal (Arctocephalus gazella and A. tropicalis).

Commercial sealing in the 18th and 19th centuries had a major impact on the Antarctic and subantarctic fur seal populations (Arctocephalus gazella and A. tropicalis) in the Southern Ocean. The intensive and unrestricted nature of the industry ensured substantial reductions in population sizes and resulted in both species becoming locally extinct at some sites. However, both species are continuing to recover, through the recolonization of islands across their former range and increasing population size. This study investigated the extent and pattern of genetic variation in each species to examine the hypothesis that higher levels of historic sealing in A. gazella have resulted in a greater loss of genetic variability and population structure compared with A. tropicalis. A 316-bp section of the mitochondrial control region was sequenced and revealed nucleotide diversities of 3.2% and 4.8% for A. gazella and A. tropicalis, respectively. There was no geographical distribution of lineages observed within either species, although the respective Phi(ST) values of 0.074 and 0.19 were significantly greater than zero. These data indicate low levels of population structure in A. gazella and relatively high levels in A. tropicalis. Additional samples screened with restriction endonucleases were incorporated, and the distribution of restriction fragment length polymorphism (RFLP) and sequence haplotypes were examined to identify the main source populations of newly recolonized islands. For A. tropicalis, the data suggest that Macquarie Island and Iles Crozet were probably recolonized by females from Marion Island, and to a lesser extent Ile Amsterdam. Although there was less population structure within A. gazella, there were two geographical regions identified: a western region containing the populations of South Georgia and Bouvetoya, which were the probable sources for populations at Marion, the South Shetland and Heard Islands; and an eastern region containing the panmictic populations of Iles Kerguelen and Macquarie Island. The latter region may be a result of a pronounced founder effect, or represent a remnant population that survived sealing at Iles Kerguelen.</p

Postsealing genetic variation and population structure of two species of fur seal (Arctocephalus gazella and A. tropicalis)

Commercial sealing in the 18th and 19th centuries had a major impact on the Antarctic and subantarctic fur seal populations (Arctocephalus gazella and A. tropicalis) in the Southern Ocean. The intensive and unrestricted nature of the industry ensured substantial reductions in population sizes and resulted in both species becoming locally extinct at some sites. However, both species are continuing to recover, through the recolonization of islands across their former range and increasing population size. This study investigated the extent and pattern of genetic variation in each species to examine the hypothesis that higher levels of historic sealing in A. gazella have resulted in a greater loss of genetic variability and population structure compared with A. tropicalis. A 316-bp section of the mitochondrial control region was sequenced and revealed nucleotide diversities of 3.2% and 4.8% for A. gazella and A. tropicalis, respectively. There was no geographical distribution of lineages observed within either species, although the respective ΦST values of 0.074 and 0.19 were significantly greater than zero. These data indicate low levels of population structure in A. gazella and relatively high levels in A. tropicalis. Additional samples screened with restriction endonucleases were incorporated, and the distribution of restriction fragment length polymorphism (RFLP) and sequence haplotypes were examined to identify the main source populations of newly recolonized islands. For A. tropicalis, the data suggest that Macquarie Island and Iles Crozet were probably recolonized by females from Marion Island, and to a lesser extent Ile Amsterdam. Although there was less population structure within A. gazella, there were two geographical regions identified: a western region containing the populations of South Georgia and Bouvetøya, which were the probable sources for populations at Marion, the South Shetland and Heard Islands; and an eastern region containing the panmictic populations of Iles Kerguelen and Macquarie Island. The latter region may be a result of a pronounced founder effect, or represent a remnant population that survived sealing at Iles Kerguelen