Sotaro Hara's research while affiliated with Kyoto University and other places

The South China giant salamander, Andrias sligoi, is one of the largest extant amphibian species worldwide. It was recently distinguished from another Chinese species, the Chinese giant salamander, Andrias davidianus, which is considered Critically Endangered according to the International Union for Conservation of Nature (IUCN) Red List. It appears too late to save this extremely rare and large amphibian in situ. Another extant species of the same genus, Andrias japonicus, inhabits Japan. However, the introduction of Chinese giant salamanders into some areas of Japan has resulted in hybridization between the Japanese and Chinese species. During our genetic screening of giant salamanders in Japan, we unexpectedly discovered four individuals of the South China giant salamander: two were adult males in captivity, and one had recently died. The last individual was a preserved specimen. In this study, we report these extremely rare individuals of A. sligoi in Japan and discuss the taxonomic and conservational implications of these introduced individuals.

Variation in morphological traits of anurans has evolved due to the pressures imposed by inhabiting different environments. The Japanese stream toad, Bufo torrenticola, breeds in running water, such as mountain streams, where the larvae grow. This lotic-breeding habit of B. torrenticola was suggested to have evolved from a lentic-breeding ancestor. Evolutionary shift of breeding habit from lentic- to lotic-breeding caused larval morphological changes to adapt to the stream habitat. However, morphological adaptation associated with the larval habitat of these three types of Japanese toads has not been explored well. In this study, we applied geometric morphometrics and distance measurements to compare body and eye characters among the tadpoles of three Japanese toads. The results showed that B. torrenticola has more dorsally and posteriorly positioned eyes, and a longer and wider rostrum because of having a larger mouth and more-developed oral muscles than its close relatives. These characters might be related to lotic lifestyle. Meanwhile, tadpoles of B. torrenticola and its sister taxon B. japonicus japonicus showed similar eye growth pattern, supporting their close phylogenetic relationship. Some of the lotic-adapted characters have also been reported in other lotic tadpoles, which is indicative of convergent evolution among stream-adapted tadpoles.

For a long time, it has been debated whether the two giant salamanders, Andrias japonicus from Japan and A. davidianus from China, are conspecific or heterospecific. Morphological information about their diagnostic characteristics has been limited, without considering sexual dimorphism and/or body size variation. Recently, A. davidianus, which was introduced into Japan sometime in the past, has been found to hybridize with A. japonicus in situ. Taxonomic identification of individuals involved in this unusual breeding is made based on mitochondrial and nuclear DNA analyses. This identification method is time-consuming and costly. Thus, developing easier methods of identification, such as utilizing external morphological characteristics, is urgently needed. In this study, we verify previous descriptions showing that A. davidianus has a longer relative tail length than A. japonicus, and the tubercles on the lower jaw and throat were present in both sexes of A. davidianus. In addition, many head characteristics were found to be relatively larger in A. davidianus than in A. japonicus, which were new distinguishing characters. These morphological differences help support the idea that these are heterospecific lineages. In hybrids, relative values of head width and tail length were larger than those of A. japonicus, and the tubercles on their lower jaw and throat were present as in A. davidianus, suggesting that the hybrids and A. davidianus are distinguishable from A. japonicus.

The Anderson's crocodile newt, Echinotriton andersoni, is an endangered species distributed in the islands of Central Ryukyus, Japan. This species is well known to show high intraspecific genetic variation among islands, but its morphological variation has not been explored. We examined the skull variation in this species including enigmatic specimens collected from Taiwan by using geometric morphometrics, and found sexual differences and geographic variation mainly between the Okinawa group (Okinawajima Island) and the Amami Group (Amamioshima and Tokunoshima Islands). We further found close resemblance between the Taiwanese specimens and the female specimens from Amamioshima Island.

This study described the detailed osteological features of the Setouchi salamander Hynobius setouchi. H. setouchi, which is endemic to central Japan, was recently delineated from the wide range of H. nebulosus species based on molecular and external morphological characteristics. However, the osteological features of the species belonging to the genus Hynobius have not been examined, which has hindered the detailed understanding of morphological diversity in the genus. To address this problem, this study elucidated the osteological features of the salamander using micro‐computed tomography scanning and whole‐mount double staining methods. The articular, a part of the hypobranchial I, a part of coracoid, pubis, carpus, and tarsus were cartilaginous in small‐sized individuals and were partially or completely ossified in large‐sized individuals. The degree of ossification varied in the operculum, basibranchial II, and ascending process of the palatoquadrate. However, ossification was not associated with body size. The lacrimal, ossified manus, and ossified pes exhibited varying degrees of articulation or fusion irrespective of body size. Moreover, the cranium and tarsus of H. setouchi exhibited several unique characteristics. These osteological characteristics will aid in revising the taxonomy and phylogeny of the Hynobius species.

Taxonomic identification of two Taiwanese salamanders, Hynobius sonani (Maki, 1922), and H. formosanus Maki, 1922, was clarified. Based on the descriptions and measurement data in the original description, we confirmed that H. sonani has been treated as H. formosanus and vice versa, which might have been caused by confusion of sampling localities of the two species. Because we could not find the holotypes of the two species and concluded these were lost, we herein assign neotypes for these species for precluding future taxonomic confusion.

The hynobiid salamander genus Hynobius is a basal taxon in the urodeles that plays a key role in understanding the evolution of sexual dimorphism in urodeles. We examined the age (juveniles vs. adults) and sexual differences in the external and skeletal morphology of a Japanese lentic breeding salamander, Hynobius setouchi. We found that juveniles had larger heads than those of adults, and most characters were larger in adult males than in females, except for trunk size. This was also observed in skeletal morphology, although some tail characters differed only in the skeleton. We suggest that intra- and interspecific comparisons of the external and skeletal characters of salamanders should consider age, sexual, and seasonal differences.