The ventral skin of the wild Japanese newt Cynops pyrrhogaster is creamy at metamorphosis, but turns red when mature. The color of the ventral skin of laboratory (lab)-reared newts stays yellow throughout their life. However, the mechanism for the red coloration of this animal still remains unknown. In this study, we have performed ultrastructural and carotenoid analyses of the red ventrum of wild and lab-reared Japanese newts. Using electron microscopy, we observed a number of xanthophores having ring carotenoid vesicles (rcv) and homogenous carotenoid granules (hcg) in the ventral red skin of the wild newt. In the skin, beta-carotene and five other kinds of carotenoids were detected by thin-layer chromatography (TLC). In the ventral yellow skin of lab-reared newts, however, only beta-carotene and three other kinds of carotenoids were found. The total amount of carotenoids in the red skin of the wild adult newt was six times more than that of the yellow skin of the lab-reared newt. Moreover, rcv were more abundant in xanthophores in red skin, but hcg were more abundant in yellow skin. These results, taken together, suggest that the presence of carotenoids in rcv in xanthophores is one of the critical factors for producing the red ventral coloration of the Japanese newt C. pyrrhogaster.

Lines of arrested growth (LAGs) appearing in bone sections are useful for age estimation. They also indicate the past growth process in amphibians in temperate zones. Several back-calculation formulae (BCFs) use LAGs to estimate an individual's body size at an earlier time based on the current body size. In order to evaluate the validity of these BCFs, we conducted a mark-recapture and skeletochronological study of female Rana japonica in Higashi-Hiroshima, Japan, from 1995 to 1999. The body sizes of 31 recaptured frogs were back-calculated using eight different BCFs and were compared with the frogs' actual body sizes as measured at the previous capture. The most accurate estimation was made by the simplest BCF (Dahl-Lea method) without any regressions between body size and bone diameter; that is, Li=Lc(Di/Dc) (L: snout-vent length, D: bone diameter, c: at the time of capture [recapture], i: at the i-th winter).

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.

The age distribution of Cynops pyrrhogaster was studied by skeletochronology on 12 breeding populations inhabiting altitudes ranging from 120 m to 1140 m on Shikoku Island, Japan. In populations inhabiting altitudes 500 m or less, the mean SVL were smaller than in those that lived at higher altitudes. In populations inhabiting altitudes less than 500 m, minimum age at maturation was three years. In populations inhabiting altitudes of 500 m or more, the minimum age at maturation was four to seven years. The number of testes lobes was influenced by age and body size and was variable among populations.

Hiroshima and Aomori populations of Buergeria buergeri (hereinafter abbreviated as HIROSHIMA and AOMORI, respectively) were morphologically differentiated in both sexually matured frogs and tadpoles. The mean snout-vent lengths of females were 67.4 mm in HIROSHIMA and 50.4 mm in AOMORI, and those of males were 42.9 mm in HIROSHIMA and 37.2 mm in AOMORI. The mean body weights of females of HIROSHIMA and AOMORI just after spawning were 18.0 g and 7.2 g, and those of males of HIROSHIMA and AOMORI were 4.9 g and 3.8 g, respectively. AOMORI tadpoles were rather stocky and their appearance seemed to be more adaptive to lentic water than HIROSHIMA tadpoles. The lower lip of the tadpoles at stage XIII consisted of 2 continuous and 1 broken teeth rows in HIROSHIMA, whereas 3 continuous and 1 broken ones in AOMORI. The growth rate of the embryos was higher in AOMORI than in HIROSHIMA. The embryos of AOMORI were more tolerant to high temperature and less tolerant to low temperature than those of HIROSHIMA. Hybrids between these two populations showed considerably reduced viability in either combination of reciprocal crosses.