Hynobius shinichisatoi Nishikawa & Matsui, 2014
|Species Description: Nishikawa K, Matsui M 2014 Three new species of the salamander genus Hynobius (Amphibia, Urodela, Hynobiidae) from Kyushu, Japan. Zootaxa 3852: 203-226.|
The body length is about three times that of the head. A groove runs along the spine and becomes deeper near the tail (Sato 1954). There are 13 or 14 costal grooves between the axilla and groin. The fore- and hind-limbs are long and thin. When the limbs are adpressed, male limbs are separated by 1.5 to 0.5 costal grooves and female limbs by 2.5 to 0 costal grooves. The relative finger lengths are I < IV < II < III and the relative toe lengths are I < V < II < IV < III. The fifth toes are well developed. The cloaca has a shape of a longitudinal slit. The genital tubercle on anterior cloaca is absent (Nishikawa and Matsui 2014). The tail is long and cylindrical near the base but becomes vertically flatter to the tip (Sato 1954). The tip of the tail is rounded when viewed laterally. The dorsal fin can be seen posteriorly (Nishikawa and Matsui 2014).
The head of larvae is trapezoidal in dorsal view, with a greatly depressed and sloping profile. The eyes are slightly protruded from edge of head. There is a labial fold located at the posterior two-thirds of upper jaw. The larvae have well-developed external gills. The caudal fin is higher than head and the dorsal fin is higher than ventral fin. The dorsal fin originates at middle to posterior of trunk, whereas ventral fin originates from vent. The tail tip is moderately pointed. The larvae also have robust limbs, with claws on fingers and toes (Nishikawa and Matsui 2014).
The species is most similar to H. hirosei, as they both have similar color and length. However, H. shinichisatoi has longer vomerine tooth series and a smaller and thinner body (Nishikawa and Matsui 2014). Larval and mature H. shinichisatoi have a black “claw” at the fingertip, whereas H. hirosei do not and H. shinichisatoi larvae are 20 - 30 mm longer than H. hirosei right before metamorphosis (Sato 1954). Hynobius shinichisatoi can be distinguished from the sympatric H. yatsui as H.shinichisatoi is larger and have an immaculate body, whereas H. yatsui have a marbled body. Hynobius shinichisatoi can be distinguished from true H. boulengeri, from which it was split in 2014, as H. shinichisatoi has a smaller body, V-shaped vomerine tooth series, a coiled egg sacs (Nishikawa and Matsui 2008 Curr. Herp – Notes on Clutch, 2014). The mean male snout-vent length of H. shinichisatoi is 82.9 mm whereas H. boulengeri is 93.9 mm. The shape of vomerine tooth series is V-shaped for H.shinichisatoi but U-shaped for H. boulengeri (Nishikawa and Matsui 2014). The egg sacs of H. boulengeri are banana-like (Nishikawa and Matsui 2008 Curr. Herp – Notes on Clutch)
In life, the mature salamanders have uniform purplish brown to slate grey coloration from the head to the tail (Nishikawa and Matsui 2014; Sato 1954). The ventral side is slightly lighter than the dorsal side. No markings on the body are observable. The limbs have the same color of the body (Nishikawa and Matsui 2014). Though mature salamanders have uniform coloration, newly metamorphosed salamanders often have silver spots on the dark blue body, especially at the dorsal side of the legs (Sato 1954). The iris is dark brown without marking. In preservative, the dorsal coloration usually fades to become gray brown. No other obvious change can be observed otherwise (Nishikawa and Matsui 2014).
In life, the larvae have a dark brown dorsum, usually with a beige stripe. The venter is white and almost transparent. Large black spots appear from head to tail, except for ventral side. Golden dots are scattered on tail fin. The "claws" on their digits is black. In preservative, dorsal coloration tends to fade to light brown, and golden dots fades to white (Nishikawa and Matsui 2014).
There are several differences between males and females. Males (82.9 ± 5.5 mm) tend to have shorter snout-vent length than females (84.3 ± 8.9 mm), but the difference has no statistical significance. Males tend to have a larger head, shorter trunk, and longer tail than females, but again these deviations are not statistically significant. Males significantly exceed females in the width and height of tail, and in the length of forelimb. The distance between costal grooves in males’ adpressed limbs is less separated than those in females. Tail fins and white tubercles on limbs are exclusive in breeding males. Some adults and young specimens have white dots on dorsum (Nishikawa and Matsui 2014).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
The estimated breeding season is between April and May (Nishikawa and Matsui 2008 Curr. Herp – Comparative Study, 2014) as males can be found in streams during this period. Females are less frequently found. They are lotic-breeding salamanders, meaning they breed in moving waters like streams, which are often very steep (Nishikawa and Matsui 2014). The clutch size ranges from 30 to 57 eggs laid in a long, coiled (two and a half times) string-like egg sac under stones in the water. The egg sac has a thin envelope and lacks a distinct whiptail structure, which is present in the banana-like egg sac of H. boulengeri. The egg sacs' length ranges from 190 to 242 mm. The eggs form a single row in each sac (Nishikawa and Matsui 2008 Curr. Herp – Note on clutch), are large, and do not have pigment. The eggs hatch in early summer (Nishikawa and Matsui 2014).
Like most other Hynobius species, H. shinichisatoi undergoes indirect development (Nishikawa and Matsui 2014). Larvae live in ponds or slow moving streams and usually are found under rocks and leaves (Sato 1954). Larvae are mostly nocturnal, but can be seen in the daytime in early summer (Nishikawa and Matsui 2014). The larvae usually overwinter, sometimes three times, before metamorphosing (Nishikawa and Matsui 2008 Curr. Herp – Comparative study). They metamorphose mostly in fall (Nishikawa and Matsui 2014).
Larvae consume comparatively large prey like earthworms (2014). Hynobius shinichisatoi larvae share some similarities with the cannibalistic H. boulengeri from Honshu, as they both exhibit overwintering and have a relatively wide mouth. However, H.shinichisatoi have not been found to display cannibalism (Nishikawa and Matsui 2008 Curr. Herp – Comparative study).
Survey on stomach contents of the metamorphs shows that they feed on a variety of invertebrates, such as arthropods and earthworms (Nishikawa and Matsui 2014).
Sexual maturation is probably earlier in males than in females as the median age of breeding females is 11 years old and that of breeding male is 9 years old (Nishikawa and Matsui 2014).
As a species in the genus Hynobius, H. shinichisatoi is part of Hynobiidae, one of only two salamander families that exhibit reproduction via external fertilization. As adults are never seen with larvae, the species does not appear to exhibit parental care for young, though it is unknown whether they guard eggs (Nishikawa and Matsui 2008 Curr. Herp – Note on Clutch)
Trends and Threats
Relation to Humans
Possible reasons for amphibian decline
General habitat alteration and loss
Analysis of cytochrome b gene from mitochondria and allelic frequencies of certain enzymes suggests that H. shinichisatoi is a sister group to H. stejnegeri, H. amakusaensis, and H. osumiensis. All of these species are species from Kyushu Island (Nishikawa and Matsui 2014). The eruption of Aso Volcano (1.30 - 0.09 mya) that created large pyroclastic flow eastward supposedly divided H. shinichisatoi from the other population and led to speciation (Nishikawa et al. 2005).
The species is named after Shinichi Sato, who discovered the species in the Sobo-Katamuki Mountains and studied its life history for 60 years (Nishikawa and Matsui 2014).
The species was originally classified as Pachypalaminus boulengeri (Sato 1954). After the genus Pachypalaminus was reclassified as Hynobius, the species was known as H. boulengeri (Nishio et al. 1987). There were indications of differentiations between H. boulengeri and H. shinichisatoi as early as 2008 (Nishikawa and Matsui 2008 Curr. Herp – Note on clutch), but they were not formally split until 2014 (Nishikawa and Matsui 2014).
The species occur sympatrically with H. yatsui in the Sobo-Katamuki Mountain, but is likely separated from each other by microhabitats and breeding sites (Nishikawa and Matsui 2014).
Kaneko, Y., Matsui, M. (2004). Hynobius boulengeri. The IUCN Red List of Threatened Species 2004: e.T59091A11869929. http://dx.doi.org/10.2305/IUCN.UK.2004.RLTS.T59091A11869929.en. Downloaded on 22 February 2017.
Nishikawa, K., Matsui, M. (2008). ''A Comparative Study on the Larval Life History in Two Populations of Hynobius boulengeri from Kyushu, Japan (Amphibia: Urodela).'' Current Herpetology, 27(1), 9-22.
Nishikawa, K., Matsui, M. (2008). ''A note on the clutch size and shape of egg sacs of Hynobius boulengeri from the Sobo-Katamuki Mountains, Kyushu, Japan (Urodela: Hynobiidae).'' Current Herpetology, 27(1), 29-34.
Nishikawa, K., Matsui, M. (2014). ''Three new species of the salamander genus Hynobius (Amphibia, Urodela, Hynobiidae) from Kyushu, Japan.'' Zootaxa, 3852(2), 203-226.
Nishikawa, K., Matsui, M., Tanabe, S. (2005). ''Biochemical phylogenetics and historical biogeography of Hynobius boulengeri and H. stejnegeri (Amphibia: Caudata) from the Kyushu region, Japan.'' Herpetologica, 61(1), 54-62.
Nishio, K., Matsui, M., Tasumi, M (1987). ''The lacrimal bone in salamanders of the genera Hynobius and Pachypalaminus: a reexamination of its taxonomic significance.'' Monitore Zoologico Italiano-Italian Journal of Zoology, 21(4), 307-315.
Sato, S. (1954). ''On Pachypalaminus boulengeri Thompson from Kyushu.'' Zoological Magazine, Tokyo, 63, 195-199.
Originally submitted by: Masato Hayashi, Yutong Song, Aimee Lim (first posted 2017-10-24)
Edited by: Ann T. Chang (2017-10-24)
Species Account Citation: AmphibiaWeb 2017 Hynobius shinichisatoi: Sobo-sanshouo (Japanese) <https://amphibiaweb.org/species/8216> University of California, Berkeley, CA, USA. Accessed Dec 11, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 11 Dec 2023.
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