Tatsuya Kariya

Lack of sequence variation of Y chromosome-linked loci in Steller's sea lions (Eumetopias jubatus) from Iony Island and the Kuril Islands

The Y chromosome-linked (Y-linked) genetic markers are important for understanding historical patterns of male dispersal (e.g., Tucker and Lundrigan 1996). Especially, the sex-determining region of the Y gene (SRY) is used as a marker to resolve phylogeography, population structure, and population dynamics of wild mammals (Hurles and Jobling 2001; Petit et al. 2002). For instance, Iwasa and Suzuki (2002) reported that SRY variation in Japanese red-backed moles (Eothenomyce andersonii) showed substantial geographic distribution. Geraldes et al. (2005) found high levels of nucleotide diversity in the SRY of European rabbits (Oryctolagus cuniculus). Moreover, Y-linked introns such as the DEAD/H (Asp-Glu-Ala-Asp/His) box polypeptide of the Y chromosome (DBY) and the histocompatibility Y antigen gene (SmcY) may be effective markers in phylogeographical study (e.g., Underhill et al. 2001). Steller’s sea lion Eumetopias jubatus (Schreber, 1776), a highly vagile marine mammal breeding in rookeries (e.g., Nowak 1999), is distributed along rocky continental coasts and near-shore islands from Northern California, through the Gulf of Alaska, along the Aleutian Islands, to the Kamchatka Peninsula, Kuril Islands, and the Sea of Okhotsk (Loughlin et al. 1992; Abe et al. 2005; Burkanov and Loughlin 2005; Wilson and Reeder 2005). Pups disperse from their natal rookeries within a year of their birth. Most adults, however, generally remain within 500 km of their natal rookeries (RaumSuryan and Pitcher 2002). Female Steller’s sea lions show strong enough philopatry to create a matrilineal substructure, as shown by mitochondrial DNA (mtDNA) lineage (Bickham et al. 1998), similar to that of the Atlantic walrus Odobenus rosmarus (Anderson et al. 1998) and the harbor seal Phoca vitulina (Stanley et al. 1996). In fact, there are three main geographical mtDNA lineages of the Steller’s sea lion: ‘eastern’ (California to the southeastern Gulf of Alaska), ‘western’ (Prince William Sound to the Commander Islands), and ‘Asian’ (Kamchatka Peninsula, Kuril Islands, and Sea of Okhotsk) (Bickham et al. 1998; Harlin-Cognato et al. 2006). Within local populations, genetic divergences of mtDNA sequence among rookeries are also recognized (Baker et al. 2005). Unlike mtDNA phylogeography, a study (Hoffman et al. 2006a) using autosomal microsatellites found that there was no clear genetic divergence between western and Asian stocks, suggesting that the phylogeographical difference between mtDNA and microsatellites studies was the result of higher dispersal rates by males. Male Steller’s sea lions tend to disperse longer distances from their natal rookeries (Raum-Suryan and Pitcher 2002). Consequently, greater male-mediated gene flow would explain the differences in pattern. Therefore, Y-chromosomal markers would provide an enhanced description of male-mediated gene flow. On the other hand, since Steller’s sea lion is gregarious and polygynous (e.g., Nowak 1999), the many offspring of a

Mitochondrial cytochrome b gene sequence diversity among Steller’s sea lion rookeries in the Kuril Islands and the Sea of Okhotsk

1 National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan 2 Primate Research Institute, Kyoto University, Inuyama 484-8506, Japan 3 National Marine Mammal Laboratory, AFSC, NMFS, NOAA 7600 Sand Point Way, NE, Building 4, Seattle, WA 98115, USA 4 Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai, Fuchu, Tokyo 183-8509, Japan 5 Graduate school of Fisheries Sciences, Division of Marine Environment and resources, Hokkaido University, Hakodate 041-8611, Japan 6 Laboratory of Wildlife Ecology, Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan