Hynobius fossigenus Okamiya, Sugawara, Nagano & Poyarkov, 2018
Japanese Rift Salamander, Higashi-hida Sanshouuo
|Species Description: Okamiya H, Sugawara H, Nagano M, Pooyarkov NA 2018 An integrative taxonomic analysis reveals a new species of lotic Hynobius salamander from Japan. PeerJ 6:e5084; DOI 10.7717/peerj.5084|
Hynobius fossigenus is most similar morphologically to other Japanese lotic Hynobius species, but can be diagnosed based on its size and breeding behaviors. Hynobius fossigenus is large, and its size allows it to be distinguished from the Taiwanese congeners H. fucus, H. formosanus, H. glacialis, H. arisanensis, and H. sonani. Hynobius fossigenus breeds in mountain streams like other lotic-breeding Hynobius species, but they lay a small clutch of 12 to 16 yellow-colored eggs. Egg sacs have a crescent or loosely spiraled shape with a smooth envelope that has a vivid blue-violet iridescent hue in water and terminate in a whip-like tail; this egg sac morphology is only observed for members of the H. kimurae-H. boulengeri species complex. Many other Hynobius species have completely dark dorsal colorations, occasionally with minimal light markings. Hynobius fossigenus, however, has a blackish-violet dorsum with tiny yellow spots, making it easily distinguishable from most other lotic species. Hynobius kimurae is the sister species of H. fossigenus, but the males and females of the latter species are consistently larger than those of H. kimurae. Vomerine teeth in H. fossigenus form a narrow U-shape, and are composed of 43 - 66 teeth in both sexes; H. kimurae, however, has long V-shaped teeth (Okimiya et al. 2018).
In life, the dorsum is dark violet-brown to black. The ventral side is paler than the dorsal side. There are distinct golden spots of varying sizes speckled across the dorsum from the head to the tail. Spots are smaller in size and fewer in number on the limbs and tail. The ventral surface lacks spots. The irises are dark brown. The vent is gray in hue and tinged with blue (Okimiya et al. 2018).
In preservation, Hynobius fossigenus did not exhibit many color changes. The dorsal markings became a beige color, and the pink tint of the underside faded to light gray (Okimiya et al. 2018).
Males are smaller than females, with heads that are shorter and wider. Males have tails that are relatively longer and thicker, and a shorter trunk length. Males have longer forelimbs than females. Some males may have 12 costal grooves instead of 13. Males’ cloacal areas are noticeably more swollen than females’ during the breeding season. Variation also exists in the number of golden spots on the dorsum (Okimiya et al. 2018).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
Hynobius fossigenus reproduce underwater, beneath stones in the stream. After copulation, females lay crescent or loosely spiraled shape egg sacs in pairs that terminate in a whip-like tail and attach them under big stones. They may also attach them onto smaller stones that are close to a waterfall. The egg sacs are very thick and appear iridescent when in water. Egg sacs contain12 to 16 yellow-colored eggs. While females leave the streams after oviposition, males linger in the streams and can often be found underneath the same stone with egg clutches (Okimiya et al. 2018).
Embryonic development lasts about 60 days, and larvae hatch between April to mid-May. Hynobius fossigenus adolescents remain in their larval form throughout the winter months. Many larvae in the Tokyo population metamorphose towards the end of May and early in June of the following year after overwintering the last stages of their development. Older larvae have been observed to cannibalize younger larvae (Okimiya et al. 2018). Larvae feed on larval caddis flies and mayflies, amphipods, and sometimes prey on conspecifics (Okimiya et al. 2018).
After undergoing complete metamorphosis, H. fossigenus prey on insects and other smaller invertebrates like spiders and earthworms. Males take at least 5 years to mature in the Tokyo population, while females require at least 7 years (Okimiya et al. 2018).
In life, larval H. fossigenus have a golden-brown dorsum and are covered with multiple dark brown spots. The ventral surface is pale surface and has no spots (Okimiya et al. 2018).
Trends and Threats
Possible reasons for amphibian decline
General habitat alteration and loss
Hynobius fossigenus is a sister species to H. kimurae, and both are members of the H. kimurae–H. boulengeri species complex. Phylogenetic analyses – using both Maximum Likelihood estimates and Bayesian Inference – of 16S rRNA, tRNA(Glu), and cyt b, mitochondrial gene fragments and RAG1 nuclear gene fragments was used to support the monophyly of this species complex. The observed level of genetic divergence between H. fossigenus and other lotic Hynobius points to a species level of differentiation. It’s estimated that the split between H. fossigenus and its sister species, H. kimurae , was approximately 5.2 million years ago. The next closest species is H. boulengeri (Okimiya et al. 2018).
The species epithet, "fossigenus", is derived from the Latin word “fossa” which means “pit” or “hollow”, and “-genus” meaning “born in;” this alludes to the distribution of the species, as they are located on either side of the Itoigawa-Shizuoka Tectonic Line, Fossa Magna’s western boundary. It is thought that the uplifting of the Central Highlands in the Fossa Magna area in the early Pliocene resulted in the geographic split between H. fossigenus and H. kimurae (Okimiya et al. 2018).
In Japanese, the common name is Higashi-hida Sanshouuo (Okimiya et al. 2018).
Okimiya, H., Sugawara, H., Nagano, M., Poyarkov, N. A. (2018). "An integrative taxonomic analysis reveals a new species of lotic Hynobius salamander from Japan." PeerJ [link]
Originally submitted by: Heidi Kim (2021-11-03)
Description by: Heidi Kim (updated 2021-11-03)
Distribution by: Heidi Kim (updated 2021-11-03)
Life history by: Heidi Kim (updated 2021-11-03)
Trends and threats by: Heidi Kim (updated 2021-11-03)
Comments by: Heidi Kim (updated 2021-11-03)
Edited by: Ash Reining (2022-10-24)
Species Account Citation: AmphibiaWeb 2022 Hynobius fossigenus: Japanese Rift Salamander <https://amphibiaweb.org/species/8868> University of California, Berkeley, CA, USA. Accessed Oct 3, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 3 Oct 2023.
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