Hynobius fossigenus
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| Hynobius fossigenus | |
|---|---|
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| An adult male | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia |
| Order: | Urodela |
| Family: | Hynobiidae |
| Genus: | Hynobius |
| Species: | H. fossigenus |
| Binomial name | |
| Hynobius fossigenus Okamiya, Sugawara, Nagano & Poyarkov, 2018 | |
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| Its distribution is comprised by the area in red. | |
| Synonyms | |
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Hynobius luteopunctatus (partim) | |
Hynobius fossigenus is a species of salamander in the family Hynobiidae, and is found in some prefectures in Kantō and Chūbu districts in Japan.
Like all species in the genus Hynobius, it has lungs, its tail is smaller than its body, and it does not have claws on its fingertips. However, characteristics such as its purplish coloration with golden spots, its size, and its use of lotic waters to reproduce make this species different from all the others.
The individuals breed between December and April in mountain streams surrounded by Cryptomeria japonica evergreen forests. After mating, the females lay their eggs in envelopes, which are thick, transparent, and resistant, where they remain for sixty days, when the embryo fully develops in the egg. After hatching, the tadpoles leave the envelope and start living under rocks or at the bottom of streams, completing their metamorphosis within a year. The males become adults around the age of five, while the females become adults around the age of seven.
The species was described in the scientific journal PeerJ on June 21, 2018, by researchers Hisanori Okamiya, Hirotaka Sugawara, Masahiro Nagano, and Nikolay A. Poyarkov.[1] It is treated as belonging to the genus Hynobius, since it has all the characteristics that together are unique to it, such as: the presence of lungs, having a tail smaller than the body, existence of clawless fingers, and the absence of a clear, visible line on the dorsal region. Speciation can be determined by its large size, by laying its eggs in lotic waters, by the thickness of its egg sac, by its small head and slender body, and by its coloration. Genetic tests were also made from its nuclear and mitochondrial DNA, as well as from mitochondrial 16S RNA, which attested that it is indeed a new species.[2]
The holotype, which was an adult male, was found on March 1, 2018, in a stream on the eastern slope of Mount Hinode in the town of the same name in Japan at an elevation of 679 meters. Also used in the description were 25 paratypes, 17 males and eight females, which were collected during the breeding season in the surrounding regions of the town where the holotype was found.[3]
Since 1986, there were already suspicions that the species existed, when researchers Ikebe, Yamamoto, and Kohno, when analyzing different populations of Hynobius kimurae, noticed a certain difference in the karyotype between individuals, in addition to a phylogenetic proximity of this species with H. boulengeri. Later, in another study in 1991, Ikebe and Kohno detected that this heterogeneity was located in the Kantō district, in addition to noticing several distinctions between the groups, such as the number of eggs per clutch and the biology of the tadpoles. Despite all these dissimilarities, the species was not described at that time, and the data was attributed to mere divergences between distinct population groups.[2]
The species' specific epithet is an agglutination of the Latin words fossa, meaning abyss, and genus, meaning born in, forming an adjective that loosely translates as one born in the abyss, a reference to the fact that it is found near a fault between the North American Plate and the Eurasian Plate.[2]
Distribution and conservation
The species can be found in several prefectures in Japan, such as Gunma, Saitama, Tokyo, Kanagawa, Yamanashi, Shizuoka, Nagano, and Aichi. Many of these populations are isolated from each other by landforms such as massifs. It is present between the altitude range of 300 and 1 100 meters, but is most common between 400 and 900 meters. It is usually close to lotic waters, such as streams, where they lay their eggs. Although the species is not protected by any law or environmental park, with the exception of the Gunma prefecture, it has a wide distribution, and only a few isolated populations may be threatened by anthropogenic actions or habitat loss, making it a least-concern species (LC). It has not yet been assessed by the International Union for Conservation of Nature (IUCN).[2]
Speciation
| Evolutionary irradiation | ||||||||||||||||||
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| Cladogram showing its speciation from a specific complex. |
Through genetic tests performed on the species, it was possible to determine that speciation occurred from the adaptive radiation of the specific H. kimurae-H. boulengeri complex, which occurred seven million years ago, at the end of the Miocene. Such radiation was caused by the appearance of mountains of volcanic origin, which separated the complex into three different groups: the western, which gave rise to H. kimurae, the central, H. boulengeri, and the eastern, H. kimurae. These populations, being reproductively isolated, and due to natural selection, began to diverge and became separate species.[2]
