Tamotsu Kusano

Testes size and breeding systems in Japanese annrans with special reference to large testes in the treefrog, Rhacophorus arboreus (Amphibia: Rhacophoridae)

SummaryTestes size was compared among 19 species of Japanese anurans in relation to their breeding systems. Although the mean body mass of the species examined varied markedly between 1.8 and 116 g, the mean proportion of testes mass to body mass was fairly constant at 0.2 to 0.4% across all species except the rhacophorid species. Foam-nest building rhacophorids had relatively large testes constituting more than 1% of their body mass. Among them, Rhacophorus arboreus had the largest, exceeding 5% of the body mass. Multi-male breeding, where a female is grasped by two or more males during spawning, occurs frequently in these rhacophorids, especially in R. arboreus. This close association between large testes size and multi-male breeding strongly suggests that sperm competition is an important factor affecting the evolution of relative testes size in Japanese anurans.

Postmetamorphic growth, survival, and age at first reproduction of the salamander,hynobius nebulosus tokyoensis Tago in relation to a consideration on the optimal timing of first reproduction

The postmetamorphic growth and survival of the salamanderHynobius nebulosus tokyoentis Tago were surveyed in the study site located in Habu village of Hinodemachi, a suburb of Tokyo City, during 1975–1981. A laboratory experiment on the growth rate of juveniles was conducted in parallel with the field survey. The result indicated that this salamander grew at the rate of 8,mm in s.v.l. per year during the juvenile stage, but its growth rate decreased markedly as low as 1.8 mm for males and 1.1 mm for females, once it had attained sexual maturity. According to the “capture-recapture” procedure the annual survival rate after metamorphosis was found to be quite high; that is, approximately 0.7. By using the growth rate of juveniles and the difference between the sizes at metamorphosis and sexual maturity, the age at first reproduction was estimated to be 4 year for males and 5 year for females. From the data obtained in this study, the intrinsic rates of increase (r) were calculated for various values of age at first reproduction under different survival schedules, and the relationship between the age at first reproduction and fitness as measured byr was examined. The result indicated that an optimal age maximizing fitness always existed under respective survival schedules, and the observed age at first reproduction of this salamandei was found to coincide well with the predicted optimal age.

Size-related cannibalism among larval Hynobius nebulosis

Cannibalistic behavior among Hynobius nebulosus larvae living in a small pond was analyzed using a videotape recording system. Maximum and range of victim size increased with cannibal size. Mouth morphology, i.e., the mouth width of a cannibal relative to the head width of the victim, is an important constraint determining maximum victim size. Time required for a cannibal to swallow its victim varied considerably among trials; there was a significant positive correlation between handling time and size ratio in total length of the victim to the cannibal. Factors affecting the rate of cannibalism in natural populations are discussed. ia, 1985(2), p. 472-476

Long-Term Trends toward Earlier Breeding of Japanese Amphibians

Abstract Recently, declines in amphibian populations all over the world have been reported. Global warming has the potential to become one of the most important causes for those declines, because reproductive activities of amphibians are affected severely by temperature and rainfall. It has been reported that climate warming has promoted a long-term tendency toward earlier breeding among amphibian populations in Europe and North America. However, some studies have not supported such a long-term change in the timing of amphibian breeding in those areas. We analyzed long-term data sets (12- to 31-year period) on the date of first spawning for four populations of three Japanese amphibians (Hynobius tokyoensis, Rana ornativentris, and Rhacophorus arboreus) in the suburbs of Tokyo and detected a significant trend toward earlier breeding in all populations examined. We also detected that the date of first spawning was correlated strongly with the mean monthly temperature just before the breeding season for each population examined. Given that the long-term trend of warming in the study district was significant, our investigation demonstrated that climate warming has affected the timing of breeding in at least some species or populations of amphibians in East Asia.

Growth and survival rate of the larvae ofHynobius nebulosus Tokyoensis Tago (Amphibia, Hynobiidae)

Growth and population density of the larvae,Hynobius nebulosus tokyoensis Tago, were estimated in a small pond within the study site settled in Habu village of Hinodemachi, a suburb of Tokyo City, during the period from 1975 to 1980. The mortality factors which influenced the survival rate of larvae were also evaluated from the ecological point of view. Laboratory experiments on the growth of larvae and predation by newts were conducted in pararell with the field survey. The results showed that growth rate of larvae under the natural condition was very slow, as compared with that under the laboratory condition with sufficient food supply, and mean body size at metamorphosis was negatively correlated with the density at that time. This suggested that food resources were in short supply in the pond, and there occurred a severe intraspecific competition for food among larvae. The mortality rate of larvae was so high, 80–99% in each year, and the density of larvae survived until metamorphosis varied so greatly from year to year that the larval stage was the most important stage throughout the life cycle to the maintenance of a population for this salamander. The most important factors which contributed to this high mortality were the predation by the newt,Triturus pyrrhogaster pyrrhogaster Boie, and cannibalism. From the laboratory experiment, it was found that predators could attack only small larvae successfully, and successful attack rate decreased sharply as larvae grew larger. This relationship resulted in the characteristic L-shaped pattern of survivorship curve of larvae; that is, heavy mortality just after hatching period.

Fluctuation in abundance and age structure of a breeding population of the Japanese brown frog, Rana japonica Günther (Amphibia, Anura)

Abstract A breeding population of Rana japonica was studied at a marsh on the campus of Hiroshima University in Higashi-Hiroshima during the five years 1995-1999. The mark-recapture study showed that the size of the breeding population varied from year to year, and increased more than twofold in 1999 in comparison with the preceding years. The sex ratio of the breeding population (male/female) was from nearly 1.0 to 1.6. Frogs of both sexes were estimated to breed for the first time at the age of one or two years, and their maximum age was four years according to skeletochronology using phalanges and mark-recapture. Modes of the estimated ages were one year for males during the study years except 1997, but one or two years for females. Two thirds of breeding frogs, irrespective of their sex, were estimated to breed only once throughout their lives.

Dispersal of the Salamander, Hynobius nebulosus tokyoensis

natural history of four species of whiptail lizards, Cnemidophorus (Sauria: Teiidae) in Trans Pecos, Texas. Southwest. Natural. 2:105-121. . 1957b. Some aspects of competition in natural populations of whiptail lizards (genus Cnemidophorus). Texas J. Sci. 410-447. MITCHELL, J. C. 1976. Niche overlap and ecology of bisexual and parthenogenetic Cnemidophorus (Sauria: Teiidae). Masters Thesis, Arizona State Univ., Tempe. 145 pp. . 1979. Ecology of southeastern Arizona whiptail lizards (Cnemidophorus): population densities, resource partitioning and niche overlap. Can. J. Zool. 57:1487-1499. OPPENHEIM, R. W. 1968. Color preferences in the pecking response of newly hatched ducks (Anos platyrhynchos). J. Comp. Physiol. Psychol. Monogr., Suppl. 66 (pt. 2):1-17. PIANKA, E. R. 1970. Comparative autecology of the lizard Cnemidophorus tigris in different parts of its geographic range. Ecology 51:703-720. RAND, A. S., G. C. GORMAN, AND W. M. RAND. 1975. Natural history, behavior, and ecology of Anolis agassizi. Smith. Contr. Zool. 176:2738.

Breeding and egg survival of a population of a salamander,Hynobius nebulosus tokyoensis Tago

(1) A population of a salamander,Hynobius nebulosus tokyoensis Tago was studied at Habu, Hinodemachi, in Tokyo during the breeding seasons from 1976 to 1978. Adults appeared in the pond were captured and marked individually by toe-clipping. Egg sacks were counted and tagged with vinyl tapes for the marking. (2) The annual egg production of this population was found to be constant, about 6500 eggs, and total number of breeding adults appeared in the pond also varied little during three years. (3) The appearance of breeding adults in the pond and oviposition seemed to be influenced by the rise of temperature and rainfall. (4) Males appeared earlier in the pond and stayed there for approximately 10 to 20 days. On the other hand, females appeared later in the pond and left there soon after laying eggs. (5) Mean clutch size and body length of breeding adults appeared in the pond showed a tendency to decrease as time proceeded, which seemed to show that the smaller and younger the salamander was, the later it appeared in the pond. (6) Owing to low temperature, the eggs laid earlier took more time to hatch than those laid later. (7) The survival rate of eggs was 67.2% in 1976, 86.4% in 1977 and 81.2% in 1978. The loss rate of eggs laid in the early and late periods of oviposition was higher than that of eggs laid in the middle period. A population of a salamander,Hynobius nebulosus tokyoensis Tago was studied at Habu, Hinodemachi, in Tokyo during the breeding seasons from 1976 to 1978. Adults appeared in the pond were captured and marked individually by toe-clipping. Egg sacks were counted and tagged with vinyl tapes for the marking. The annual egg production of this population was found to be constant, about 6500 eggs, and total number of breeding adults appeared in the pond also varied little during three years. The appearance of breeding adults in the pond and oviposition seemed to be influenced by the rise of temperature and rainfall. Males appeared earlier in the pond and stayed there for approximately 10 to 20 days. On the other hand, females appeared later in the pond and left there soon after laying eggs. Mean clutch size and body length of breeding adults appeared in the pond showed a tendency to decrease as time proceeded, which seemed to show that the smaller and younger the salamander was, the later it appeared in the pond. Owing to low temperature, the eggs laid earlier took more time to hatch than those laid later. The survival rate of eggs was 67.2% in 1976, 86.4% in 1977 and 81.2% in 1978. The loss rate of eggs laid in the early and late periods of oviposition was higher than that of eggs laid in the middle period.

Body Size and Age Structure of Breeding Populations of the Salamander, Hynobius tokyoensis (Caudata: Hynobiidae)

ABSTRACT Body size and age structure were studied for two breeding populations of the salamander, Hynobius tokyoensis, in the southern Kanto plain of Honshu, Japan. The mean snout-vent lengths (SVLs; measured from the tip of snout to the posterior end of cloaca) of males and females were 64.1 and 66.5 mm at Habu in Tokyo, and 63.1 and 65.3 mm at Isumi in Chiba prefecture, respectively. The differences in SVL were not significant between sexes or populations. The breeding adults, successfully aged by skeletochronology using phalanges, were 4–21 years old. The median age was significantly older in the Habu population (eight years) than in the Isumi population (five years), and the age at first reproduction estimated from the age at which the growth of individuals was greatly retarded was two to six years. The modal age at first reproduction was four years for both sexes in both populations except for males at Isumi (three years). In the latter, age at first reproduction was significantly younger than in the others. We discuss the ecological significance of interpopulational variation in age structure clarified by skeletochronology.

Seasonal succession of a microphagotroph community in a small pond during litter decomposition

Temporal dynamics of a lentic microphagotroph community were studied during leaf litter decomposition from December to May. Small plastic vessels containing leaf litter were placed on a pond bottom. They were sampled periodically to collect microphagotrophs. Three abiotic factors and abundance of two food items were also measured to analyze the autogenic and allogenic phenomena during a microphagotroph succession. Three behavior types were recognized in dominant taxa: a free-swimming type, a vagile (creeps on substratum, sometimes swims) type, and a voluntarily fixed type. Dominant taxa changed from the free-swimming to the vagile type up to mid-March, and the reverse change occurred from mid-April. Principal component analysis (PCA) indicated four factors affecting the dynamics of the community: water temperature as a seasonal factor, detritus volume on the litter surface as a habitat factor, and densities of bacteria and small flagellates as food factors. Taxa replacement appeared to occur through two mechanisms. (1) Dominance of small holotrichs, a free-swimming type, was brought about by a high bacterial density caused by seasonal events, i.e., leaf fall in December and detritus formation by litter feeders in mid-April. This is an allogenic aspect of community dynamics. (2) The free-swimming type was replaced by the vagile one during the period with high taxa diversity. This replacement occurred through intertaxa competition for scarce food and/or selective predation by larger microphagotrophs. It is an autogenic process within the community.