Yasuchika Misawa

Age Determination by Skeletochronology of the Japanese Salamander Hynobius kimurae (Amphibia, Urodela)

Abstract We investigated lines of arrested growth (LAG) of long bone tissues in a total of 157 salamanders of Hynobius kimurae from Tokyo and Kyoto, Japan. The number of LAGs did not differ between femurs, humeri, and toe phalanges. We found that the first LAG is formed after the first overwintering. The number of LAGs varied from 5–14 (x¯=8.8) in reproductive males and 7–12 (x¯=9.4) in mature females in the Tokyo population, while in the Kyoto population, males and females had 6–20 (x¯=9.1) and 7–17 (x¯=9.9) LAGs, respectively. This suggests that the minimum maturation age in males is five yr in Tokyo and six yr in Kyoto, while females of both populations need at least seven yr. The female-larger sexual size dimorphism, recognized in each population of this species seems to be attributable to a greater growth rate in females after the age of male maturity. Body size growth was better in Kyoto than in Tokyo, with average adult SVL being 3.2–3.6 times and 2.2–2.3 times of SVL of metamorphs, respectively. Adults of the Kyoto population, like metamorphs, are smaller than those of the Tokyo population, and such a difference is considered to be derived not from the differential age at maturity or growth rate but from the size difference at metamorphosis. In both populations, clutch size does not correlate to female age, but older and hence larger females tended to lay larger eggs. This suggests that the female fitness increases with age, not through an increase in the number of offspring per clutch, but through an elevation of survivorship per offspring.

Age Determination by Skeletochronology of Rana nigrovittata, a Frog from Tropical Forest of Thailand

Abstract Age in 96 individuals of a tropical frog Rana nigrovittata from Thailand was skeleto-chronologically investigated. Hematoxylinophilic lines interpreted as lines of arrested growth (LAGs) were observed clearly in the periosteal bone suggesting that this technique can be used to estimate the age of frogs from tropical Asia. The maximum age observed was nine years in males and six in females, but age structure did not differ significantly between the sexes. In the same age class, males were significantly larger than females.

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

Abstract 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.

A Comparison of Age Structures in Two Populations of a Pond Frog Rana nigromaculata (Amphibia: Anura)

Abstract Using skeletochronology, we compared age structure in the breeding season in two populations (Katata, Shiga Pref. and Shizuhara, Kyoto Pref.) of a pond frog, Rana nigromaculata from central Japan and elucidated interpopulation variation in some life history traits. Newly metamorphosed froglets were larger in SVL, heavier in body mass, and fattier in Katata than in Shizuhara. In both populations, the age at first reproduction was 2 yrs for males and 3 yrs for females. Longevity was estimated to be at least 5 and 6 yrs at Katata and Shizuhara, respectively, for both sexes. Females were on an average significantly older than males in both populations. The modal age in breeding males was 2 yrs in Katata but 4 yrs in Shizuhara, and Katata males (mean=3.27 yr) tended to be younger than Shizuhara males (mean=3.42 yr), although the difference was not significant. Similarly, females did not differ in the mean age in the two populations (4.1 yrs in both populations). In SVL, females were significantly larger than males in both populations. In males, SVL was larger in Shizuhara than in Katata, but females did not differ in SVL. Shizuhara males grew faster than Katata males, but females did not differ in growth rate in both populations. Interpopulation differences in age and size properties of R. nigromaculata seem to be related to degree of interspecific competition and food consumption. We briefly discussed use of skeletochronology in relation to amphibian declining problems.

Allozymic variation of Hynobius kimurae Dunn (Amphibia, Caudata)

An electrophoretic survey was conducted to examine genetic divergence among 21 populations of a lotic-breeding salamander Hynobius kimurae from Honshu, Japan. Genetically H. kimurae proved to be specifically distinct from H. naevius. Hynobius kimurae is divided genetically into two groups of local populations, and the five populations from the eastern area are genetically distinct from the remaining populations of the central and western areas. Less prominent genetic differentiation was revealed between the western and central populations. Separation of the eastern and central-western groups are discussed in relation to the formation of the Japanese mainland.

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

Taxonomic status of a salamander now identified as Hynobius tokyoensis from Aichi Prefecture, Japan, was assessed by allozymic comparisons with its relatives. All three populations of H. tokyoensis from Aichi formed a monophyletic group with populations of H. nebulosus; this group is substantially diverged from a conspecific population from Kanagawa that formed another group with H. lichenatus. In the former group, the population of H. nebulosus from near the type locality was more divergent from the other conspecific populations than were three populations of H. tokyoensis from Aichi. It is quite clear that the salamander from Aichi now identified as H. tokyoensis is genetically much closer to H. nebulosus than to H. tokyoensis from Kanagawa, which is closest geographically to its type locality. This result conforms well to reported results of morphological and genetic studies, and the salamander from Aichi, now called H. tokyoensis, should be identified as H. nebulosus, which is sufficiently diverged from H. tokyoensis to be considered a distinct species.

Phylogeny and historical demography of Cynops pyrrhogaster (Amphibia: Urodela): taxonomic relationships and distributional changes associated with climatic oscillations.

We investigated the phylogenetic relationships and estimated the historical demography of the Japanese fire-bellied newt, Cynops pyrrhogaster, from Japanese mainlands using 1407-bp sequences of the mitochondrial DNA (NADH6, tRNAglu, cyt b) and 1208-bp sequences of nuclear DNA (Rag-1) genes. Phylogenetic trees based on mitochondrial DNA revealed four major haplotype clades (NORTHERN, CENTRAL, WESTERN, and SOUTHERN clades) within this species. Degree of genetic differentiation among major haplotype clades was very large for intraspecific variation, suggesting this species to be composed of four species lineages that replace each other geographically. Nuclear genetic variation presented no obvious patterns of geographic structure except for the distinctness of populations diagnosed by NORTHERN clade of mitochondrial haplotypes, suggesting results of incomplete lineage sorting. Current distribution and estimated divergence times for the genus Cynops suggest that the common ancestor of two Japanese species (C. pyrrhogaster and C. ensicauda from the Ryukyu Islands) had diverged at the edge of the continent corresponding to the present East China Sea and Central Ryukyus. Subsequent range expansion to Japanese mainland seems to have occurred in the middle Miocene. Population-genetic analyses indicated that all species lineages, except for the SOUTHERN one, experienced geographic population reductions and expansions associated with glacial and postglacial climatic oscillations.

A New Species of Salamander of the Genus Hynobius from Central Honshu, Japan (Amphibia, Urodela)

Abstract We describe a small salamander from south Central Honshu, Japan, as a new species, Hynobius katoi. The genetic distances between this species and several named species, including sympatric H. kimurae, derived from allozyme data from a starch gel electrophoresis, proved to be sufficiently large to differentiate it at a specific rank. Distribution of this species is confined to the montane regions of Shizuoka and Nagano Prefectures, on the Akaishi Mountains of the Chubu District, central Japan. It is regarded as a member of the naevius group of Hynobius, characterized by small number of large, pigmentless ova. The species differs from the other species of the naevius group by the combination of relatively small body size, nearly spotless body, relatively few vomerine teeth forming moderately shallow series, and unique electrophoretic pattern of isozymes.

Age determination of Daruma pond frog, Rana porosa brevipoda from Japan towards its conservation (Amphibia: Anura)

The age of a vulnerable frog, Rana porosa brevipoda from Japan was estimated using the now classical technique of skeletochronology. The mean age did not differ between the sexes but males were smaller in body size than females. Sexual maturity was attained in the fall of the year of metamorphosis in males and in the breeding season of the next year in females, and both sexes began to breed in the next year of metamorphosis. Both sexes similarly had minimum longevity of four years. The population age composition showed a rapid decrease in number of frogs with the increase of age. Growth parameters differed between sexes and males grew more rapidly and sexually matured at a smaller size than females. We comment on the peculiar pattern of postmetamorphic survival curves in R. porosa brevipoda as a threatened species. We also discuss the reason of decline in this species and suggest a measure of conservation.

Age determination of wrinkled frog, Rana rugosa with special reference to high variation in postmetamorphic body size (Amphibia : Ranidae)

Abstract Individual ages of postmetamorphic R. rugosa from three populations of Kyoto, Japan (Gondoike, Iwakura, and Kiyotaki), were determined skeletochronologically. From recaptured individuals, one LAG was confirmed to be formed per year. In all three populations, age at sexual maturity was 1–2 yrs in males and 2–3 yrs in females, though some females matured at the age of 1 yr. Longevity was at least 4 yrs in males and 5 yrs in females. Sexual size dimorphism was conspicuous in adults, and females were invariably larger than males. Females had a larger asymptotic size than males but growth rate differed between some localities only in males. In all populations, both sexes showed high variations in SVL and the variation was even higher in juveniles than in adults. This high variation is explained by a prolonged breeding season and resultant mixture of metamorphs with and without overwintering larval stage within a population of this species.