Age determination by skeletochronology of the Japanese giant salamander Andrias japonicus (Amphibia, Urodela)

In the past several years, a number of studies have been carried out on the behavioral and reproductive ecology of the Japanese giant salamander Andrias japonicus, but the age and longevity of A. japonicus has not yet been studied. In this study, we attempted to establish an age determination method using specimens (age: 1 to 11 years old) from Hiroshima City Asa Zoological Park that lived and died in captivity. The cross sections of phalangeal bones were nearly circular in shape, and hematoxylinophilic lines that were interpreted as lines of arrested growth (LAGs) were observed in the periosteal tissue; this suggests that this technique can be used to estimate the age of A. japonicus. The number of LAGs was one less than the number of winters that each individual experienced. We could observe LAGs in both frozen and 10% formalin specimens. LAGs could be confirmed even for specimens that had been fixed in formalin for up to 30 years. By using this method, it was suggested that the lifespan of this species could be determined from specimens existing in museums, zoos, and aquariums worldwide. It also showed potential for providing important conservation information, such as generation time and age structure of populations in the field.This work supported by JSPS KAKENHI Grant Numbers JP 26870400, JP 17K 01209

Practical Study for Conservation of Giant Salamander Andrias japonicus in Toyosaka, Higashi-Hiroshima, Japan <Article>

オオサンショウウオAndrias japonicus は,日本の固有種であり国の特別天然記念物である。環境省のレッドリストでは絶滅危惧Ⅱ類(VU)に指定され,全国的に生息状況の悪化が危惧されている。東広島市豊栄町椋梨川においても,河川の人工化等によりその数が減少し,保護活動の担い手の高齢化に伴い,本種の生息状況に関する情報が極めて乏しい状況であった。そこで,本河川での本種の分布・生態を明らかにする野外調査を実施した。その結果,2011 年からの約2年間の調査で成体21個体と幼生10個体を確認し,本河川が本種の生息地であるだけでなく貴重な繁殖地であることを確認した。しかし,幼生を除けば全長60 - 86cm の大型個体しか確認されず,弱齢個体の個体群への新規加入が正常に起こっていない危険性も示唆された。本稿では,本河川における本種の現状が危機的であることを具体的に報告し,本種の保全にむけた持続的な活動の構築を目指した普及活動の成果と課題についても報告する。The giant salamander Andrias japonicas, which is endemic to Japan, is ranked as vulnerable. It is designated as a national special natural monument. Information on the giant salamander in Higashi-Hiroshima city is extremely scarce. To determine the current habitat of A. japonicas, we surveyed the Mukunashi River including areas where the giant salamander had lived in the past. Our surveys did find 21 adults and 10 larvae of A. japonicas within a two year period (from 2011 to 2013). However, we did not discover any young individuals of total length of 50 mm - 600 mm. This suggests that larval recruitment is not successful. This paper specifically reports that a critical situation exists for the giant salamander in the Mukunashi River in Higashi-Hiroshima City. And the publicity work aiming at conservation and its result are also reported

A population of the Japanese giant salamander Andrias japonicus (Amphibia: Caudata) inhabiting a small stream flowing through a wetland upstream of a dam: A study on the population of small individuals and larval growth in the field

広島県廿日市市飯山のダム上流の湿地を流れる小河川に生息するオオサンショウウオAndrias japonicusの個体群について報告する。本産地は標高が775–795mあり，本種の生息地で最も標高の高い部類に入る。飯山貯水池は1932年より水力発電ダム湖として建造され，その上流は約90年間ダムの下流域と隔離されている。水位の低下した2001年以降は長年人の手の加わっていない湿地となっている。2017–2020年ののべ17日間に渡る調査で，0歳から1歳，2歳と考えられる幼生が多数見つかり，全長210mmの幼体や326–680mmの成体，繁殖巣穴も見つかった。これは独立した繁殖個体群として世代交代している証拠でもある。この個体群からは全長700mmを越える個体が見つかっておらず，全長が小さい傾向がある。また，0歳幼生の全長と確認日の関係を見ると，全長46mmで離散した0歳幼生が，6月から8月にかけて急成長して75mmに達し，10月以降はほとんど成長しないで翌春を迎えることを示唆していた。幼生は主にダム湖であった当時の名残の水草，ヒルムシロPotamogeton distinctusの中から見つかる傾向がある点も特異な点である。ダム湖へ直接流入する源流域の小河川で本種が持続的に繁殖している例として本産地と個体群は稀少な存在であると言える。Here, we describe a population of the Japanese giant salamander Andrias japonicus inhabiting upstream of the Iinoyama Reservoir in Iinoyama, Hatsukaichi City, Hiroshima Prefecture, Japan. The locality is situated at 775–795 m above the sea level and is one of the highest localities in the habitat of this salamander. The Iinoyama Reservoir was originally built as a hydroelectric dam lake in 1932, and its upstream part has remained isolated for nearly 90 years. Since 2001, when the water level dropped, it has become a wetland, albeit not used by human for many years. In surveys over 17 days during 2017–2020, many zero-, first-, and second-year larvae; a juvenile 210 mm in total length (TL); and adults (326–680 mm in TL) as well as a breeding nest were found, providing evidence that the salamanders in this regions constitute an independent breeding population. No individuals measuring over 700 mm in TL were found in this population, and the overall TL tended to be low. Considering the association between the total length and the date of discovery of zero-year larvae, these larvae likely dispersed when they were about 46 mm and rapidly grew from June to August to reach 75 mm; from October, however, they barely grew until the next spring. Interestingly, the larvae were found in the remnants of the dam lake, near the aquatic plant Potamogeton distinctus. The described locality and population present a rare example of continuous breeding of the Japanese giant salamander in a small stream directly flowing into the dam lake

Development of Microsatellite Markers for the Two Giant Salamander Species (Andrias japonicus and A. davidianus)

The Japanese giant salamander (Andrias japonicus) is a near threatened species endemic to western Japan and is strictly protected by law. However, available information regarding the genetic diversity and genetic structure in this species, essential for its effective conservation, has been limited. We developed four microsatellite markers from A. japonicus and characterized these markers for two populations of this species, as well as for some captive Chinese giant salamanders (A. davidianus) of unknown original locality or localities. These markers, showing expected heterozygosities of 0. 00–0. 50 in the former and 0. 63–0. 89 in the latter, will be useful in documenting population genetic properties for each of the two species

Preoviposition paternal care in a fully aquatic giant salamander: nest cleaning by a den master

Parental care in salamanders is thought to be simple and typically limited to female egg attendance. No elaborate preoviposition parental care had been described from salamanders. Recent studies revealed complex care behaviours by male Japanese giant salamanders (Andrias japonicus), a fully aquatic, secretive species with external fertilization. These studies emphasize behavioural convergence in paternal care between some of the fish species and the giant salamanders. The fish examples further imply the possibility that males of A. japonicus provide preoviposition parental care in the form of nest cleaning and building. We tested this possibility and also predicted that cleaning effort by a male salamander, if exists, would increase as it approaches the spawning event. Prior to the breeding season, large males (i.e. den masters) of A. japonicus occupy and guard suitable burrows well-hidden along the stream bank. In the falls of 2012, 2013 and 2015, we videotaped and examined a single den master’s pre- and postoviposition behaviours at Asa Zoological Park in Hiroshima, Japan. The den master repeatedly exhibited vigorous movements of front and hind limbs in a paddling motion at the bottom of the nest every day for the three separate years. The cleaning effort by the den master lineally increased as the spawning event approached, after which the den master completely ceased cleaning. With the cleaning behaviour, the den master made the den filled with debris including leaves and twigs buried in the sand. The floating debris was subsequently removed by the water current flowing through the nest. Water mould infection is a major cause of offspring mortality of aquatic amphibians including A. japonicus. By reducing the amount of organic matter that provides food sources for water mould, the nest cleaning likely reduces the risk of water mould infection among the offspring, serving as an important preoviposition parental care