Systematic status of Hynobius tokyoensis (Amphibia: Urodela) from Aichi Prefecture, Japan: a biochemical survey

Fine-Scale Genetic Differentiation in a Salamander Hynobius tokyoensis Living in Fragmented Urban Habitats in and Around Tokyo, Japan

Salamanders are expected to differentiate genetically among local populations due to their low dispersal ability, and are potentially susceptible to loss of genetic diversity if the population is isolated by habitat fragmentation. The salamander Hynobius tokyoensis is a lowland lentic breeder and endemic to a narrow area of central Japan. In this urban area, H. tokyoensis habitats are extensively fragmented and several populations are threatened with extinction, but information on genetic divergence and loss of genetic diversity is scarce. We performed mitochondrial (cyt b) and microsatellite (five loci) DNA analyses of 815 individuals from 46 populations in 12 regions across their entire distribution range. As a result, populations were clearly separated into northern and southern groups, and genetic differentiation among the 12 regions was also evident. Regional differentiation appears to be affected by a complex geographical history, but the genetic diversity of each population may have also been affected by recent habitat fragmentation. There were positive correlations between the mitochondrial and microsatellite DNA diversities. Some populations have lost genetic diversity in both mitochondrial and microsatellite DNAs; all such populations were at the peripheral edges of the species distribution range. Thus, even in attempts to restore genetic diversity in a small population by the transfer of outside individuals, efforts must be made to avoid genetic pollution.

Population Structure and Evolution after Speciation of the Hokkaido Salamander (Hynobius retardatus)

The Hokkaido salamander (Hynobius retardatus) is endemic to Hokkaido Island, Japan, and shows intriguing flexible phenotypic plasticity and regional morphological diversity. However, to date, allozymes and partial mitochondria DNA sequences have provided only an outline of its demographic histories and the pattern of its genetic diversification. To understand the finer details of the population structure of this species and its evolution since speciation, we genotyped five regional populations by using 12 recently developed microsatellite polymorphic markers. We found a clear population structure with low gene flow among the five populations, but a close genetic relationship between the Teshio and Kitami populations. Our demographic analysis suggested that Teshio and Erimo had the largest effective population sizes among the five populations. These findings regarding the population structure and demography of H. retardatus improve our understanding of the faunal phylogeography on Hokkaido Island and also provide fundamental genetic information that will be useful for future studies.

Population structure of the salamander Hynobius retardatus inferred from a partial sequence of the mitochondrial DNA control region

We investigated population structure of the salamander Hynobius retardatus in Hokkaido, Japan using partial sequences of the mitochondrial DNA control region (490 bp) from 105 individuals. The salamanders were collected from 28 localities representing the entire regional distribution of this species. Twenty different haplotypes distributed across three haplotype groups were identified. Group 1 was widely distributed in central, northern, and eastern Hokkaido, except Erimo; Groups 2 and 3 appeared exclusively in Erimo and southern Hokkaido, respectively. The genetic distance between the three groups was not very large, but the distributions of the groups never overlapped spatially, indicating a hierarchical population structure comprising three regional groups, which was also supported by analysis of molecular variance. The results suggest that the present population structure is affected by current genetic barriers, as well as by historical transitions of climate and landscape.

Genetic relationships among salamanders of the genus Hynobius (Amphibia, Caudata) from Korea and southwestern Japan

We performed allozyme analysis for three Korean (Hynobius leechii, H. quelpaertensis, and H. yangi) and three Japanese (H. nebulosus, H. tsuensis, and H. dunni) salamanders to clarify their interspecific relationships using H. naevius as an outgroup. The genetic distances (Nei's D) within ingroup species ranged from 0.11 to 0.78 with a mean of 0.33. In the NJ and CONTML trees, monophyly of the ingroup was not supported and Korean H. quelpaertensis and H. leechii diverged first from the remaining species, which together formed a weakly supported clade. Korean H. yangi, long identified as H. leechii, was closer to Japanese H. nebulosus (D=0.108) and H. tsuensis (D=0.138) than to Korean H. leechii (D=0.197) and H. quelpaertensis (D=0.305). Hynobius tsuensis and H. nebulosus were very close (D=0.108) despite their different breeding habits. A geohistorical hypothesis is proposed to explain the divergence of the six species.

Systematic Relationships of Hynobius okiensis among Japanese Salamanders (Amphibia: Caudata)

We conducted an electrophoretic survey to examine systematic relationships of a lotic-breeding salamander Hynobius okiensis endemic to Dogo Island of the Oki Islands, Japan, with several lentic and lotic-breeding Japanese species. Genetically H. okiensis with 2n=56 chromosomes was closer to the lentic-breeding H. nebulosus group (H. nebulosus and H. dunni) with the same chromosome number than to the lotic-breeding H. naevius group (H. naevius and H. kimurae) and H. boulengeri with 58 chromosomes. Chromosome number reduction from 58 to 56, possibly accompanied with a change in breeding environment from streams to still waters, is estimated to have first occurred in the nebulosus group of Hynobius. A reversal only in breeding habits then seems to have followed in steep, montane environments of the small island of Dogo, resulting in the speciation of H. okiensis.

Morphological and Allozymic Variation in Hynobius boulengeri and H. stejnegeri (Amphibia: Urodela: Hynobiidae)

We studied morphological and allozymic variation in populations of Japanese salamanders, Hynobius boulengeri and H. stejnegeri. Adult H. boulengeri showed sexual dimorphism, and juveniles differed greatly from adults in many morphological characters. From the results of multivariate analyses of morphological characters, the populations were divided into four groups: (I) H. boulengeri from Honshu, (II) H. boulengeri from Shikoku, (III) H. boulengeri from the Sobo-Katamuki Mountains of Kyushu and H. stejnegeri, and (IV) H. boulengeri from the Amakusa Islands and the Osumi Peninsula. Phenotypic relationships among the four groups were identical to relationships clarified by allozymic analyses, except for group IV, which was included in group III in the allozyme tree. Some morphometric characters were significantly correlated with environmental variables. We consider H. stejnegeri to be a valid species based on its unique color pattern, morphometric characters, and allelic composition, even though it was nested within group III of H. boulengeri by both morphological and allozymic analyses. We propose that group I from Honshu and group II from Shikoku should be treated as H. boulengeri sensu stricto and H. hirosei, respectively. Resolving the taxonomic status of the remaining populations of groups III and IV from Kyushu requires further study.

Occurrence of Two Types of Hynobius naevius in Northern Kyushu, Japan (Amphibia: Urodela)

A survey to examine genetic variation among Hynobius naevius from four localities of Fukuoka Pref., northern Kyushu, Japan, resulted in the detection of two, sympatric, genetic types (A and B) that are clearly different in the allelic frequencies of four loci (ACOH-A, ACOH-B, ADH-A, and SOD-A) in each locality. Morphological investigations between the two genetic types also proved that they are clearly discriminated; the type A is about 75 mm in SVL, lacks mottling pattern on bluish purple dorsum, and possesses relatively short vomerine teeth series, while the type B is about 60 mm in SVL, and has light mottling on reddish purple ground color. These results strongly suggest that reproductive isolation occurs between these two types, and that they could be regarded as separate species. Populations from Toyota-cho, western Honshu, and Yabe-machi, central Kyushu, both close to Fukuoka Pref., were very similar to the types A and B, respectively. From these results, we consider that two evolutionary lineages that first evolved allopatrically in western Honshu and southern Kyushu secondarily contacted and became sympatric in the region of northern Kyushu.