On the main islands of Japan, two closely related colubrid snake species, the Japanese rat snake (Elaphe climacophora) and the Japanese striped snake (E. quadrivirgata), coexist in sympatry. These species differ in habitat utilization: E. climacophora is semi-arboreal, while E. quadrivirgata is mostly terrestrial. Due to the differences in habitat utilization of the two species, I hypothesized that E. climacophora would exhibit superior climbing ability to E. quadrivirgata. To test this, I conducted two behavioral experiments in captivity. In Experiment 1, I compared the climbing speed of adult individuals of both species on a vertical surface formed by a 45-degree intersection of a plywood board and a wall. In Experiment 2, I tested whether hatchlings of the two species were able to climb a 90-degree corner formed by two intersecting walls. The results showed that, in adults, the hypothesis that E. climacophora climbs faster than E. quadrivirgata, independent of size differences, was only partially supported, while in juveniles, E. climacophora exhibited significantly higher climbing success rates than E. quadrivirgata. Overall, these findings suggest that E. climacophora possesses superior climbing ability across life stages. As a future direction, I briefly discussed a potential link between differences in climbing ability and differing patterns of avian prey exploitation.

Anuran tadpoles perceive predation risk in the environment from the types of semiochemical cues emitted by both predators and prey, and they perform various defensive responses to reduce encounter probabilities and increase the escape probability after predator attacks. While the impact of simple stimuli, such as the presence or absence of predation risk, on defensive responses has been extensively studied, the influence of quantitative gradients and the interaction of these cues on defensive responses is less understood. In this study, we reared Dryophytes leopardus tadpoles in environments with varying numbers of predatory dragonfly nymphs, Orthetrum albistylum speciosum, and tadpole prey conspecifics to examine how different levels of stimuli affect the defensive responses of tadpoles. The cue from prey consumed by nymphs triggered a decrease in tadpole activity. The two cues interact in a complex way which affects how the tadpole responded. Increased prey-borne cues result in induced increases in total length and tail length in the tadpoles when there was one predator nymph, but no effect was detected when there were two nymphs. Our results indicated that D. leopardus tadpoles perceive quantitative variations in cues of different origins and respond to varying levels of predation risk in a more complex manner than we had expected.

Understanding population dynamics is critical for the management of animal populations. Comparatively little is known about the relative importance of endogenous (i.e., density-dependent) and exogenous (i.e., density-independent) factors in the population dynamics of amphibians with complex life cycles. A breeding population of the Japanese salamander, Hynobius tokyoensis, has been monitored at Habu in Hinode-machi, Tokyo, from 1975 to 2025. The number of breeding females was estimated annually by counting the total number of egg sacs deposited in a pond. Female abundance varied from year to year and ranged from 35 to 160 during this period. Time-series data of population abundance were analyzed using state-space modeling to estimate the strength of the effects of density dependence and climatic conditions on population dynamics, owing to the presence of plausible temporal autocorrelation. I used the exponential growth state-space model and the Ornstein-Uhlembeck state-space model as proxy models for density-independent and density-dependent population growth, selecting between them using the parametric bootstrap likelihood ratio test. The hypothesis of density independence was rejected for the study population (5,000 bootstraps, P=0.0026), and the Gompertz state-space (GSS) model, incorporating both density dependence and climate effects, was applied to the time-series data. The analysis using the GSS model also demonstrated a significant negative effect of climatic factors, such as relative humidity, in the preceding growth season. The present study shows the importance of both density-dependent and density-independent climate effects on the long-term dynamics of the breeding population of H. tokyoensis, and suggests the possibility that density dependence may buffer the salamander population against environmental stress.

For tropical ectotherms invading temperate regions, cold stress imposes significant negative impacts on their activity and survival. A previous study demonstrated that the recent northward range expansion of Hemidactylus frenatus to Amamioshima Island, Japan, after 2000 was driven by climate change rather than acquisition of stronger cold tolerance: the ambient temperature on Amamioshima after 2000 has increased compared to that on Okinawajima Island prior to 1955, where H. frenatus has long persisted. Two other gecko species of tropical or subtropical origin, H. bowringii and Gehyra mutilata, established populations on Amamioshima around the 1950s–1960s, suggesting they possess stronger cold tolerance compared to H. frenatus. To test this hypothesis, we compared cold tolerance among the Amamioshima populations of these three species, representing the current northernmost limits of their distributions, through laboratory experiments. Results showed significant differences in critical thermal minimum (CTmin) among the three species: G. mutilata exhibited the highest CTmin (11.35±0.34°C), whereas H. bowringii showed the lowest CTmin (8.58±0.40°C) and H. frenatus exhibited intermediate values (10.36±0.55°C). These findings suggest that G. mutilata persists in Amamioshima via behavioral thermoregulation, most likely relying on anthropogenic heat sources to survive the cold winter there. In contrast, H. bowringii may have stronger cold tolerance inherently or acquired locally, allowing this species to spread across Amamioshima in the 1960s. Rising ambient temperatures with climate change after 2000 enabled H. frenatus to establish a stable population on this northernmost island.

Delimiting species is crucial, especially for threatened and understudied organisms, because unresolved taxonomy can result in unrecognized species diversity and misallocated conservation efforts. In this study, we used an integrative taxonomic approach, incorporating genetic, morphological, and acoustic analyses, to clarify the phylogenetic relationship of the endangered Short-legged Horned Toad (Boulenophrys brachykolos) from South China. We focused on individuals from three geographically separated regions in Hong Kong, one on the mainland (Kowloon) and two on islands (Lantau Island and Hong Kong Island). Our genetic data identified Lantau Island individuals to be an evolutionarily distinct lineage, with a minimum genetic difference of 2.1% from other populations. Acoustic analysis revealed that male B. brachykolos from Lantau Island produce calls with similar frequency, but significantly higher pulse and note rate. However, morphological comparisons did not reveal significant differences among the three regions. To conclude, the B. brachykolos population from Lantau Island may represent a case of speciation in progress, and in the interim, should be treated as a distinct conservation unit.

Species of Ichthyophis, from East, Southeast, and South Asia, are difficult to identify, mainly because many species were described based only on a few specimens without examining intraspecific variation. We redescribe I. biangularis, an endemic species of Malaysian Borneo. The morphology of the newly collected topotype is consistent with the original description. The phallodeum and the larvae are first described in this study. We sequenced Cyt b of mitochondrial DNA of this topotype and genetically identify the specimens collected in adjacent areas to the type locality. Intraspecific genetic variation of the species is relatively high compared to another species in this genus. We also describe the natural history of this species, including its habitat and reproduction.

Reproductive processes, including spermatogenesis and vitellogenesis, have been closely associated with the migratory and behavioral patterns of sea turtles. However, whether physiological changes associated with reproduction influence behavioral adaptations, particularly swimming and feeding patterns, remains unclear. Thus, this study aimed to examine the relationship between reproductive cycles (spermatogenic and vitellogenic) and behavioral patterns (swimming and feeding) in captive loggerhead turtles, Caretta caretta. Experiments were conducted from January 2011 to December 2012 at the Okinawa Churaumi Aquarium and involved one male and two female loggerhead turtles. Monthly measurements included serum testosterone levels in the male and triglyceride and total protein concentrations in the females. Behavioral observations of swimming and feeding were recorded to calculate activity ratios. Distinct seasonal variations were observed in the male and female turtles. In the male, testosterone levels and swimming activity increased from December, peaked during the mating season (March to April), and declined thereafter. Feeding activity decreased during the peak reproductive phase (February to April) and recovered after mating in May. In the females, triglyceride and total protein levels, along with swimming activity, increased during vitellogenesis (October to February) and peaked during nesting (March to April), whereas feeding behavior declined during these periods. These findings underscore the synchronization between reproductive cycles and behavioral changes, suggesting that hypophagic behavior facilitates energy allocation for reproduction. This may make it possible to estimate the reproductive and physiological cycles of captive loggerhead turtles based on simple behavioral observations that do not cause stress to the turtles, thereby leading to the implementation of successful captive breeding programs.

Amphibians are poorly dispersed owing to their low osmotic-pressure and salt tolerance, and are rarely found on islands. However, amphibians that invade islands through anthropogenic introduction can have high population densities and enormous impact on native ecosystems. Bufo formosus, a large Japanese amphibian, was artificially introduced as a nonnative species, mainly on islands, and has had a significant impact on the native ecosystems of Hokkaido and Sado Island. However, knowledge of this introduced species on the Izu Islands is limited. Therefore, in this study, we conducted distribution and habitat-density surveys and created a species distribution model (SDM) to clarify the distribution status of introduced nonnative B. formosus on Miyake-jima Island, where approximately 20 years have passed since a volcanic eruption and species invasion. Occurrence record surveys revealed that B. formosus was found in a wide area of Miyake-jima Island. While SDM predicted that this species inhabits not only in forest but also grasslands formed after volcanic eruption, it was predicted that the potential distribution probability of this species inhabiting coastline and summit areas were low. A population density survey revealed the highest density around Tairo Pond on Miyake-jima Island, where 538 toads were found in 10 minutes. The lack of predators and competitors for this species on Miyake-jima Island may explain its widespread and high-density population. In the future, it will be necessary to clarify the impact of such a high-density population on the native ecosystem, especially on insect fauna.