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 natur e of the industry ensured substantial reductions in population sizes and re sulted in both species becoming locally extinct at some sites. However, bot h species are continuing to recover, through the recolonization of islands across their former range and increasing population size. This study invest igated the extent and pattern of genetic variation in each species to exami ne 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 d istribution of lineages observed within either species, although the respec tive 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 r elatively high levels in A. tropicalis. Additional samples screened with re striction endonucleases were incorporated, and the distribution of restrict ion fragment length polymorphism (RFLP) and sequence haplotypes were examin ed to identify the main source populations of newly recolonized islands. Fo r A. tropicalis, the data suggest that Macquarie Island and Iles Crozet wer e probably recolonized by females from Marion Island, and to a lesser exten t Ile Amsterdam. Although there was less population structure within A. gaz ella, there were two geographical regions identified: a western region cont aining the populations of South Georgia and Bouvetoya, which were the proba ble sources for populations at Marion, the South Shetland and Heard Islands ; and an eastern region containing the panmictic populations of Iles Kergue len 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.