Alternative Titleユーラシア東部におけるヒグマの分子系統地理学的研究
Note (General)The mammal fauna of the Japanese islands, especially Hokkaido had experienced the repeated colonization of the animals from the Eurasian Continent during the Pleistocene glacial periods. T he brown bear ( Ursus arctos ) is widely distributed on the Holarctic region, and occurs only on Hokkaido and adjacent southern Kuril Islands (Kunashiri and Etorofu) in Japan . To clarify the migration history of the brown bears in Hokkaido and adjacent insular populations, resolving detail ed phylogenetic relationships and estimating the precise timings of the population immigrations to Hokkaido are needed . In addition, it is necessary to reveal the detailed genetic structure of the brown bears across the Eurasian Continent, which could be the evolutionary source of the Hokkaido brown bears. Furthermore, t he brown bear show s male - biased dispersal and female philopatry. Thus, most of the previous studies using maternally inherited mitochondrial DNA ( mtDNA ) markers might not represent the comp rehensive phylogeographic history of the brown bears. Considering the sex - biased migration for the evolutionary history of the brown bear is essential , and it is needed to uncover the paternal phylogeographic structuring of the brown bear . In C hapter I, c omplete mtDNA sequences of 35 brown bears from Hokkaido, the southern Kuril Islands (Kunashiri and Etorofu ), Sakhalin Island, and the Eurasian Continent ( Ural Mountains, European Russia, Bulgaria, and Tibet), and those of four polar bears were analyzed . Ba sed on these sequences, I reconstructed the maternal phylogeny of the brown bear and estimated divergence times of brown bear lineages . The brown bear on Hokkaido was divided into distinct maternal lineages (central, eastern, and southern Hokkaido), and th ree independent migrations to the island could have occurred . Although Sakhalin Island is considered to be a transient area for ancestors of the Hokkaido brown bears, the Sakhalin brown bear grouped with eastern European and western Alaskan brown bears. Thus, Sakhalin brown bear did not originate at the same time as the dispersal of brown bears into Hokkaido. Brown bears in southern Kuril Islands (Kunashiri and Etorofu) adjacent to Hokkaido Island were closely related to eastern Hokkaido brown bears, and could have diverged from the eastern Hokkaido lineage after formation of the channel between Hokkaido and the southern Kuril Islands.In Chapter II, I developed an amplified product length polymorphism ( APLP ) analysis for mtDNA - haplogrouping of brown bear specimens by detecting haplogroup - specific SNPs. U sing this newly developed method, I successfully analyzed 54 historical skin specimens up to 170 - year - old collected widely across continental Eurasia, and verified the validity of this method. Some of the same brown bear mtDNA haplogroup s as those occurring in eastern Hokkaido and eastern Alaska were found within the Eurasian Continent (Altai Mountains and Caucasus Mountains). This result shows that brown bears in eastern Hokkaido and eastern Alaska descended from a common ancestor on the Eurasian Continent, and that brown bears occupied several refugia in southern Asia during the Last Glacial Maximum. In Chapter III, t o elucidate the paternal genetic structure around northeastern Asia and assess the influence of male - mediated gene flow fo r the genetic connectivity among and within intraspecific populations, paternally inherited Y - chromosomal DNA sequences and Y - linked microsatellites of 124 brown bear s from Hokkaido, southern Kuril Islands (Kunashiri and Etorofu), Sakhalin, and the Eurasia n Continent (Kamchatka Peninsula , Ural Mountains, European Russia, and Tibet) were analyzed. The paternal lineage of Hokkaido brown bears was differentiated from those of the continental Eurasian/North American populations, and showed the lack of recent ge netic connectivity from the continental populations. Within Hokkaido Island, weak spatial genetic structuring of the paternal lineages was found, and this is supposed to be formed through male - mediated gene flow among natal populations within Hokkaido Isla nd. Different dispersal patterns between males and females of the brown bear combined with the founder effect and subsequent genetic drift could have contributed to the makeup of the brown bears on Etorofu Island, which is composed of the inconsistent orig ins of the maternal and paternal lineages. The results demonstrate that brown bear phylogeography around Hokkaido is considerably complicated than previously expected only from the mtDNA studies. The present study demonstrated the importance of using sex - specific uni - parentally inherited markers, both maternally (mtDNA) and paternally (Y - chromosomal DNA) inherited markers to study the phylogeography of the animals, especially exhibiting the extensive sexual differences in behavior .
(主査) 教授 増田 隆一, 教授 堀口 健雄, 教授 小亀 一弘, 教授 高木 昌興, 准教授 加藤 徹
理学院（自然史科学専攻）
Collection (particular)国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
Date Accepted (W3CDTF)2018-04-03T03:53:09+09:00
Data Provider (Database)国立国会図書館 : 国立国会図書館デジタルコレクション