学位論文 Population genetic structure and genetic diversity of the Japanese lentic salamanders for conservation of endangered Hynobius

Sugawara, Hirotaka

pp.1 - 88 , 2015-03-25
Salamanders are expected to differentiate genetically among local populations because they have low dispersal ability. Thus, they are potentially susceptible to loss of genetic diversity if the populations are isolated by habitat fragmentation. In addition to these factors, the urban neighborhood-dwelling species can be strongly affected by several human activities, and an immediate conservation is needed. In conservation of these species in the wild, there are three problems to solve before conservation activities: (1) taxonomic, (2) ecological, and (3) genetic problems. Especially, to clarify the four genetic matters is a great help in appropriate conservation planning: (1) genetic monitoring, (2) management unit, (3) genetic diversity, and (4) genetic pollution. In the present study, the analyses of population genetic structure including the four genetic matters are performed using both mitochondrial and microsatellite DNAs for the future conservation of the urban neighborhood-dwelling salamanders, Hynobius tokyoensis (mainly distributed in the Kanto District) and H. dunni (mainly distributed in the eastern Kyusyu). Japanese lentic Hynobius species may contain cryptic diversity and most species of this genus are generally difficult to identify without information on sample locality because of their morphological similarities. In conservation of these species, many inappropriate conservation decisions can be made if the taxonomic status is incorrect. To solve the problems, phylogenetic relationships of them were examined for 55 populations including ten lentic Hynobius species using mitochondrial 16S rRNA (1103-bp) and cytochrome b (630-bp) genes. As a result, populations were clearly separated into eastern Japan group and western Japan group with high bootstrap values. H. nebulosus may be polyphyletic species despite it may be monophyletic species based on morphological characters, but monophyly of H. tokyoensis is supported by some previous studies and the present study. Also, Kyushu populations of H. dunni may be monophyletic group, but Kochi population of H. dunni was genetically different from them. Thus, taxonomic and phylogenetic reassessment of H. nebulosus and Kochi population of H. dunni using high variable nuclear markers are needed. The salamander Hynobius tokyoensis is a lowland lentic breeder and endemic to the narrow area of central Japan. In this urban area, their habitats are extensively fragmented and several populations are threatened with extinction. Genetic management of this salamander is now needed, but information on genetic divergence and loss of genetic diversity is little available. So, mitochondrial cytochrome b (650-bp) gene and microsatellite (five loci) DNA analyses were made for 815 individuals from 46 populations in the 12 regions across their entire distribution range. As a result, populations were clearly separated into northern and southern groups, and genetic differentiation among 12 regions was also evident. Regional genetic differentiation seems to be affected by complicated geographical history, but genetic diversity of each population may be affected by recent habitat fragmentation. Some populations have lost genetic diversity in both mitochondrial and microsatellite DNAs because a positive correlation was detected between the mitochondrial and microsatellite DNA diversities. However, female-biased bottleneck effects were also evident in several populations in which mitochondrial DNA diversity was more reduced than microsatellite DNA diversity. Even if we need recovery of the genetic diversity in a small population by transferring other individuals, particularly the females, we must pay attention to avoid genetic pollution. Oita salamander Hynobius dunni Tago, 1931, endemic to eastern Kyushu and western Shikoku of southwestern Japan, is a lowland lentic breeder and has declined its distribution range. To contribute to the future conservation of this salamander, current population genetic structures and genetic diversities were examined for 12 populations of eastern Kyushu, by using a mitochondrial cytochrome b (569-bp) gene and three microsatellite loci. As a result, populations were genetically separated into northern and southern groups, and there were some genetic differences even in the northern regions based on microsatellite analysis. The southern group was restricted to the narrow area and had low genetic diversity in both mitochondrial and microsatellite DNAs. In the northern group, the mitochondrial and microsatellite DNA diversities were also low in some peripheral populations. Toward the accurate genetic management of this species, we must pay more attention to such genetic differentiation and diversity in a fine scale. The two salamander species have larger genetic differences among breeding sites and these populations are expected to conserve separately. However, closely related populations may justify management as single unit. Genetic diversities of the two species tended to decrease around the periphery of distribution range and completely isolated populations. The genetic pollution should be carefully examining when introduction to the inbred populations from other non-inbred populations for the resurrection of their genetic diversity.
低地の止水で繁殖するサンショウウオ類は,人為的な環境変化により個体群の衰退が著しく,保護が急務とされている.野生生物を保護する際,生態学的な知見 (生活史,個体群密度,個体数変動,生残率) に加えて,集団遺伝学的な知見が欠かせない.特に,集団遺伝学的モニタリング (genetic monitoring),管理単位 (management unit) の推定,遺伝的多様性 (genetic diversity) の評価,そして遺伝子汚染 (genetic pollution) の有無は,適切な保全計画を立てる上で必須の情報である.本研究では,関東に生息するトウキョウサンショウウオ (Hynobius tokyoensis) および九州東部に生息するオオイタサンショウウオ (H. dunni) に関して,将来的な保全に向けて,これら4項目を含む集団遺伝学的解析を行った.まず,トウキョウサンショウウオ46集団815個体について,ミトコンドリアDNAのcytochrome b (650-bp) および核DNAのマイクロサテライト5遺伝子座に基づく集団遺伝学的解析を行った.トウキョウサンショウウオはHynobius属の中で分子系統学的によくまとまった集団を形成し,福島南部から房総および三浦半島南部まで断続的に生息する.本種は,地理的に比較的狭い範囲に分布しているにもかかわらず,集団ごとの遺伝的差異は顕著であった.特に,北部と南部では遺伝的差異が大きく,銚子から房総半島にかけてと,栃木から東京にかけて,それぞれ異なる遺伝的な傾斜が認められた.一方,三浦半島と房総半島南部の集団は遺伝的に類似しており,両半島が陸続きであった時代に移動分散が起こった可能性を支持している.遺伝的多様性に関して,ミトコンドリアDNAと核DNAに基づく多様度を比較した結果,両者の間には正の相関が認められ,分布の周縁域でとくに遺伝的多様度が低い集団が見られた.また,埼玉集団と三浦半島集団および埼玉集団と房総半島集団の間にはそれぞれ遺伝子汚染が生じている可能性が示唆された.房総半島集団の間にはそれぞれ遺伝子汚染が生じている可能性が示唆された.次に,オオイタサンショウウオ12集団242個体において,ミトコンドリアDNAのcytochrome b (569-bp) および核DNAのマイクロサテライト3遺伝子座に基づく集団遺伝学的解析を行った.オオイタサンショウウオについては,形態分類と分子系統解析の結果が一致しなかったため,九州東部の集団のみを解析対象とした.本種もトウキョウサンショウウオと同様に,大分県から宮崎県という比較的狭い分布域にも関わらず,大きな分集団化が認められた.また,主に分布域の周縁部で遺伝子多様度の低い集団が見られた.これら都市近郊に分布する低移動性サンショウウオ類に関しては,繁殖場所ごとに遺伝的な分化が生じている可能性が示唆された.そのため,保全管理単位の決定を行う際には,比較的狭い範囲の管理単位とする必要がある.また,分布域の周縁部では,両種ともに遺伝子多様性が低い傾向があった.やむを得ずこれらの集団に対して遺伝的多様性の回復を目的とした導入を行う際には,遺伝子汚染に十分注意する必要がある.




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