著者

Sugawara Hirotaka

出版者

首都大学東京

巻号頁・発行日

pp.1-88, 2015-03-25

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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.