Diversity and hybridisation estimates in Antarctic and Subantarctic fur seals from Marion Island based on mitochondrial and microsatellite DNA markers

Abstract

The mitochondrial DNA (mtDNA) control region and 5 microsatellite loci were used to assess genetic variability and the extent of hybridization between the two fur seals (Arctocephalus tropicalis and A. gazella) that occur on Marion Island. Both species were harvested during the 18th and 19th centuries, leading to a reduction in population size and the extinction of A. gazella at some localities. Whilst both species have recovered and are increasing in size1, it is not clear to what extent sealing has affected genetic variation, although a more pronounced effect would be expected for A. gazella, given the more intensive harvesting of this species2. The current study confirmed this hypothesis and revealed that A. gazella had nucleotide diversity of 2.9 % whilst for A. tropicalis it was 4.2 %, across the HRVI region sequenced. For microsatellite DNA, genetic variation in A. tropicalis was higher than in A. gazella in terms of the total number of alleles detected and the level of heterozygosity (HE= 0.875/ Ho=0.845, mean number of alleles=13.6) and (HE=0.799/Ho=0.781, mean number of alleles=13), respectively. Diversity in both species is among the highest recorded in pinnipeds, and suggests that sealing did not overly affect the levels of genetic variation in these species3. The level of hybridization between these species was low at Marion Island with only one hybrid being detected among the 134 animals that were genetically characterized. This corresponds to 0.75 %, but may be an under­ estimate as the samples used in this study were primarily collected from sites where the two species do not co-occur. Future studies focusing on sites where they occur sympatrically, may yield higher estimates.