Several Asian natricine snakes possess special organs called nuchal glands. Previous studies showed the nuchal glands of Rhabdophis tigrinus contain cardiac steroidal toxins known as bufadienolides (BDs) that are sequestered from toads consumed as prey. Recently, a congener has been found to ingest fireflies and sequester defensive BDs from them. As amphibians are probably the plesiomorphic diet of Rhabdophis species, it is presumed that a dietary transition of toxin source from toads to fireflies has occurred within the radiation of Rhabdophis. Because snakes heavily rely on chemical cues to recognize their prey, we predicted that species of Rhabdophis are capable of detecting BDs. To test the prediction, we conducted chemical preference tests using adults and hatchlings of R. tigrinus. We presented seven stimuli (water, cologne, earthworm, cinobufagin [a compound of BDs], toad, frog, and lampyrine firefly) to them. Both adult and hatchling R. tigrinus showed a higher response to toads and frogs than the controls (water and cologne), but, contrary to our prediction, they did not respond to cinobufagin. Adult R. tigrinus did however show a higher response to lampyrine fireflies than the controls. Our data imply that chemical resemblance between toads and fireflies elicited the reaction in adult R. tigrinus, but the chemical substances remain unknown. To identify the proximate mechanisms of the unique shift from toad-eating to firefly-eating in the snakes, further investigation is necessary.
The male urogenital system of salamanders varies both among families and within them. To understand diversity of this system in hynobiids, we studied the gross anatomy and histology of the male urogenital system of a mountainous rheophilic salamander, Ranodon sibiricus. Males had single-lobed, lobular-cystic testes which were characterized by the presence of ‘lobular waves’. The sperm transport system included the vasa efferentia, longitudinal collecting ducts of the vasa efferentia, the genital kidneys, and Wolffian ducts leading to the cloaca. There were also rudimentary Müllerian ducts. The cloaca contained ventral glands. The structure of the male urogenital system of R. sibiricus was similar to the genera Batrachuperus, Hynobius, and Salamandrella.
The raccoon (Procyon lotor) was introduced to Japan from North America, and has been implicated in the population declines or local extinctions of native freshwater turtles. We conducted a capture–recapture study of the Japanese pond turtle (Mauremys japonica) at two sites in the Boso Peninsula, Japan, to investigate the effects of P. lotor predation on the demography of native turtle populations, during the period from 2014 to 2017, shortly after an invasion of P. lotor. The study revealed a steady decline in turtle population size, along with changes in age structure, characterized by a skew toward older age classes. We also found a number of living individuals with amputated limbs, which we suspect to be evidence of P. lotor predation. Such injuries highlight the importance of the early detection of population declines and identification of related warning signals or demographic characteristics, which in turn will enable the timely implementation of appropriate conservation measures to prevent local extinctions of freshwater turtles.
The diet of the nonnative American Bullfrog Lithobates catesbeianus occurring in Ogimi Village of Okinawajima, Ryukyu Archipelago, is investigated. Seventy two of 89 frogs (nine adults, five subadults, and 58 juveniles) captured had food items in its stomach. We identified a total of 64 taxa from 253 food items. Our analyses show that (1) the diet consists mainly of terrestrial prey, (2) mollusks and vertebrates are the essential prey groups for adults and subadults, and (3) odonates, mollusks, and arachnids are the main prey for juveniles. Such dietary habits are quite different from those of several conspecific nonnative populations in mainland Japan and other regions. Part of this is most likely related to the absence of the frog’s favorite prey, nonnative American crayfish Procambarus clarkii, in the study area. We also confirm the predation of a poisonous newt Cynops ensicauda popei (Salamandridae) and several aquatic insects by this frog and present some implications for these results.
Two species of frogs endemic to Japan, Rana neba and R. tagoi, have previously been separated based on differences in the number of chromosomes and the dominant frequencies of their advertisement calls. However, through a comparison of advertisement calls around the type localities of both species, we found that interspecific differences are instead apparent in the fundamental frequencies, not in the dominant frequencies. Additionally, the calls of R. neba are more easily distinguished by their unique first notes, which can be differentiated by the strong frequency modulation, longer and fewer pulses, and lower pulse rate. Compared with R. neba, the calls of R. tagoi are composed of notes with similar acoustic structure, although the last note is longer in duration, contains more pulses, and has longer inter-pulse intervals than in the other notes in the call. Based on these results, we present a new acoustic diagnosis for R. neba and R. tagoi.
The Japanese grass lizard, Takydromus tachydromoides, is a species endemic to Japan. While several studies have investigated the reproductive ecology of T. tachydromoides, the embryogenesis of this species has not been reported in detail. In the current study, we observed the external morphological characteristics of 247 embryo specimens that developed under a constant temperature (28°C) throughout the duration from oviposition to hatching. We identified 17 consecutive developmental stages for the post-ovipositional developmental process of this species based on the staging criteria that have been widely used for the description of embryogenesis of lizards. The youngest embryos on the day of oviposition corresponded to stage 26, which is a relatively early period in pharyngula stages, and juveniles hatched at stage 42, approximately 30 days after oviposition. The entire developmental sequence of key morphological features was shared with other species of Lacertidae, except for the timing of the beginning of the first body pigmentation. This is the first description of the complete sequence of post-ovipositional developmental stages for the oviparous species of Lacertidae, providing valuable information for further evolutionary developmental studies.
An invasive alien species American bullfrog (hereafter, ‘bullfrog’) is found in freshwater lakes in Onuma Quasi-National Park, Hokkaido, Japan. Bullfrog commonly feeds on red swamp crayfish in many areas. However, red swamp crayfish has not been confirmed in Komuna Lake, Onuma Quasi-National Park. The purpose of this study is to examine the trend of predation on native biomes in areas without crayfish presence. We detected the dietary composition of bullfrogs. The stomach contents of 469 individuals were analyzed and classified. The stomach contents of adult frogs accounted for 67.4% of volume were vertebrates including Actinopterygii and Amphibia such as Japanese crucian carp, topmouth gudgeon, bullfrog juveniles, bullfrog tadpoles and Japanese common toad. Further, aquatic animals were preyed more than terrestrial animals in volume (60.0%) and frequency (90.0%). From these results, bullfrogs in Onuma Quasi-National Park used most conspicuous alien aquatic species such as alien fish and frogs of the same species as food resources and further revealed that these alien aquatic species function as a substitute food for the crayfish. While the majority of bullfrog food resources are alien aquatic species, several rare aquatic animals were also preyed on. In the future, it will be necessary to investigate the predation pressure of bullfrogs on local biodiversity.
Scincella vandenburghi is a small lygosomine skink, distributed in Tsushima Island and the Korean Peninsula as well as their adjacent islands. We analyzed the within-species genetic variation among the populations of Tsushima Island, Cheju Island, and the Korean Peninsula using partial sequences of mitochondrial DNA, cytochrome b and cytochrome c oxidase subunit I genes. We detected 20 haplotypes in total. Little genetic divergence was observed among the populations of S. vandenburghi from the Korean Peninsula, Tsushima Island, and Cheju Island. Genetic diversity was low in this species and demographic statistics suggested the recent expansion of distribution. Considering that Tsushima Island has been separated from the Korean Peninsula since 0.43 million years ago and that a narrow seaway had persisted between these two areas even during the Last Glacial Maximum, the low genetic divergence in S. vandenburghi suggests that this species expanded its range from the Korean Peninsula to Tsushima Island by oversea dispersal.
Gloydius blomhoffii is a common pitviper distributed throughout Japan except for Okinawa Prefecture. To understand intraspecific geographic variation of this widely distributed snake, I describe several of its basic ecological traits observed during a 31-year-field survey conducted in the forest of Ashiu, northeastern Kyoto, in the western region of the mainland of Japan, and compare these traits with those reported in previous studies conducted in widespread areas of Japan. Body length of G. blomhoffii in Kyoto was smaller than that in the northernmost range and larger than that in the southernmost range. Sexual size dimorphism in snout-vent length, tail length, and body mass showed the same trends as in other areas. The sex ratio of the collected snakes was biased to females, which has not been observed in other studies. Pregnant females showed higher body temperature than males and non-pregnant females at a given air temperature. Parturition period, litter size, and body size of neonates generally overlapped with those reported in previous studies. Stomach contents were found only in 9.1% of snakes and consisted of rodents, frogs, and newts, which are prey items already known in G. blomhoffii. Although the forest in Ashiu has been incurred drastic environmental degradation, no obvious change in body size was detected over the study period. This study adds information on ecological traits of G. blomhoffii based on a population-level study and will facilitate future intensive field research to understand this common, but still poorly investigated, venomous snake endemic to Japan.
Bufonid toads generally possess cardiotoxic steroids called bufadienolides as defensive chemicals. Although knowledge of the life stages at which the toad species possess the poison is important for our understanding of diversity of toxicity among bufonid toads, this knowledge is limited. In the present study, we revealed that the Japanese common toad, Bufo japonicus formosus, possesses toxins at the unfertilized egg stage by conducting a bioassay experiment. Recent studies documented that hatchlings of B. j. formosus have lethal toxic effects on native frog tadpoles (Rana pirica) in the invasive area of the toad (Hokkaido). In our bioassay experiment using R. pirica tadpole as a predator, no tadpoles died when they did not consume any prey item during two-days experimental period. However, approximately 90% of R. pirica tadpoles immediately died when they consumed an unfertilized egg of B. j. formosus. These results suggest that the toxin at the early life stages of B. j. formosus is, at least partly, provided from female parent.