Phylogenetic relationships, population genetics and hybridisation of two species of southern fur seal (Arctocephalus spp.)
Creators: name: Wynen, LP
Publisher: name: University Of Tasmania
Year: 2023

description: 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 &lt; 0.000). Significant population structure was evident within the subantarctic fur seal with both the mitochondrial (