Description
Onychodactylus tsukubaensis is a cryptic, medium-sized salamander in the Hynobiidae family with a snout-vent length of 69.5 ± 3.1 mm in males and 66.9 ± 2.1 mm in females. Onychodactylus tsukubaensis males are generally bigger than females in snout-vent length and have a tail that is longer relative to snout-vent length, but sexual dimorphism is not significant. The head is oval and sunken with a length that is almost twice the width. The head is wider than the neck. Onychodactylus tsukubaensis has a rounded snout that extends farther than the lower jaw; its nares are close to the tip of the snout. The internarial distance is 7.0 - 7.5% of snout-vent length in males and 6.9 - 7.8% in females. The eye-nostril distance is 2.9 - 3.7% of snout-vent length in males and 3.1 - 3.5% in females. Onychodactylus tsukubaensis has large, protuberant eyes that are shorter than the snout and bulge out prominently almost as far as the outside edge of the upper jaw. The upper eyelid length is 5.9 - 6.4% of snout-vent length in males and 5.9 - 6.6% in females. The minimum distance between upper eyelids is 4.2 - 4.6% of snout-vent length in males and 4.0 - 5.0% in females. The interocular region has a minimum distance of 8.5 - 9.8% of snout-vent length in males and 8.9 - 9.5% in females. The postorbital groove is distinct and extends to the parotoid gland. The oval parotoid gland is well developed between the angle of the jaw and the gular fold, located posterventrally to the head and has a 1.7:1.0 ratio of length to width. Onychodactylus tsukubaensis has a relatively thick body with a trunk that is long and tubular. The forelimb is slim, and the forearm is somewhat fuller than the upper arm. From the base of the forelimb to the longest fingertip, males are 25.0 - 27.4% of snout-vent length and females are 24.4 - 28.1%. For fingers, the relative lengths are III > II > IV > I. Palmer and tarsal tubercles as well as palmer and plantar black asperities are absent. Compared to the forelimb, the hindlimb is longer and noticeably sturdier. From the groin to the longest toe tip, males measure 29.5 - 32.8% of snout-vent length and females are 28.2 - 31.9%. The thigh and tibia are approximately equivalent in thickness. Hindlimbs in females are not as hearty as in males. Distally, the end of the female’s fibula does not project as far back as in the male. During breeding season, males have a dermal skin fold on the back edge of the hindlimb. For toes, the relative length is IV = III > II > V > I. Breeding adults and larvae have horny, black claws on finger and toe tips. Distance between the forelimb and hindlimb in males is 49.7 - 53.3% of snout-vent length and in females is 48.6 - 53.6%. On both sides of the trunk, there are 11 - 12 costal grooves that are well developed and do not differ significantly between males and females. There is, however, a greater amount of overlap between the forelimbs and hindlimbs in males (about 0.8 folds) compared to females (no folds). There is a mid-dorsal groove that runs from the back of the head to a position on the back level with the cloaca. This salamander does not have a swollen cloaca. The vent is slit longitudinally with a length that is 7.1% of snout-vent length. There is a skin fold on the anterior half of the vent’s somewhat enlarged edge that resembles an inverted V-shape. Tail length ranges from 99.0 - 114.1% of snout-vent length in males and 82.0 - 95.9% in females, with no significant difference between sexes. In males, the basal tail height is 6.8 - 10.6% of snout-vent length and 8.2 - 10.1% in females. The basal tail width in males is 7.6 - 10.6% of snout-vent length and 8.7 - 10.2% in females. The medial tail height in males is 6.0 - 11.2% of snout-vent length and 7.2 0- 10.9% in females. The medial tail width in males is 5.0 - 8.3% of snout-vent length and 4.8 - 7.6% in females. At the base, the tail is cylindrical, increasing in compression posteriorly with additional lateral compression occurring in the last 75% of the tail. The tail is highest at 11.4% of snout-vent length in the last 25% of the tail (Yoshikawa and Matsui 2013).

Onychodactylus tsukubaensis larvae have a total length of 30.2 - 81.8 mm with a snout-vent length of 18.4 - 45.6 mm and a tail length of 11.7 - 39.1 mm. The head is oblong and the snout is rounded. Three pairs of small, external gills are evident. A labial fold is well developed on the back half of the upper jaw. Although low, the caudal fin is well developed on both the dorsal and ventral surfaces. Relative to the ventral fin, which is low and begins near the last 25 - 33% of the tail, the dorsal fin is higher and originates above the cloaca. The tip of the tail is somewhat rounded. There is a fold of skin on the back edge of the limbs. The palms and soles have dark asperities, and the digits have sharp claws that are black and curved (Yoshikawa and Matsui 2013).

Members of the Onychodactylus genus have a characteristically long tail that is generally much longer than the snout-vent length, compared to others in the Hynobiidae family, where the tail length is generally the same or smaller. However, besides variation in background color, O. tsukubaensis can be differentiated from O. fischeri, O. koreanus, O. zhangyapingi, and O. zhaoermii by tail length, which is shorter than snout-vent length in females and the same or only marginally longer in males in relation to snout-vent length compared to the other species. In species-specific comparisons, O. tsukubaensis males have wider and longer heads than male O. japonicus. Female O. tsukubaensis are smaller overall, have shorter tails, smaller intercanthal and internarial distances, but have longer and wider heads than female O. japonicus. Onychodactylus tsukubaensis has a significantly shorter tail than O. nipponoborealis and relative to head length, O. tsukubaensis females have a smaller interorbital distance compared to O. nipponoborealis females. Since coloration varies greatly in O. tsukubaensis and often overlaps with other species, it is difficult to differentiate this salamander from O. japonicus or O. nipponoborealis by coloring. However, O. tsukubaensis can be distinguished by its red-brown/ochre dorsal stripe with a well-defined edge and many lateral to ventral, dense silvery dots compared to topotypic O. japonicus, which has a distinct red/orange dorsal stripe and sparse silvery dots, and O. nipponoborealis, in which a defined, wide dorsal stripe and dense silvery speckling occurs less often. From other species, O. tsukubaensis has a wider head and shorter trunk than O. fischeri, O. zhangyapingi, and O. zhaoermii. Onychodactylus tsukubaensis females have lengthier forelimbs and hindlimbs and fewer costal grooves (12) than O. koreanus (13). Onychodactylus tsukubaensis also has fewer costal grooves than O. fischeri (14 – 150). Onychodactylus tsukubaensis can be further differentiated from O. fischeri, O. zhangyapingi, O. zhaoermii, and O. koreanus by its broad dorsal stripe, which is absent in these species (Yoshikawa and Matsui 2013).

Relative to snout-vent length, the tail in O. tsukubaensis larvae grows at a significantly slower rate, resulting in a somewhat shorter tail, compared to O. japonicus. The head of O. tsukubaensis larvae is commonly wider relative to head length in comparison to O. japonicus. The shorter tail and wider head make O. tsukubaensis larvae appear to be relatively heavier built than the larvae of the other two species. Distinguishing characteristics of O. tsukubaensis are the silvery speckling and mottling, which occur over the whole body, and the pale yellow, dorsal and caudal stripe, which is relatively more defined and broader than in the other species (Yoshikawa and Matsui 2013).

In life, O. tsukubaensis is generally ranges from grayish-brown to dark gray to purplish gray with a vivid red-brown to ochre dorsal stripe, that has a clearly demarcated, wavy and blotchy border. The top of the head is covered in indistinct dots that coalesce into the dorsal stripe. The stripe widens toward the back of the eye, narrows at the neck, and then widens again across the trunk, tapering towards the tip of the tail. The dorsal stripe appears mostly clearly and vividly at the base of the tail then narrows and becomes less distinct toward the tip of the tail. In alcohol, body coloration is faded and the dorsal stripe is bleached. From the side of the body to the belly, this salamander is covered in compact silvery dots. These dots also turn slightly hazy and the belly becomes whitish. The top half of the iris is evenly golden and the bottom appears black. Slightly dark coloration surrounds the vomerine teeth. In life, the salamander nymph is yellow-gray with black dots on the upper half of its body and light white and translucent on the lower half. As the nymph grows, the black spots spread out and coalesce (Yoshikawa and Matsui 2013).

In life, Onychodactylus tsukubaensis individuals vary widely in coloration. The broad dorsal stripe may be wavy, straight, or blotchy; it is rare that no stripe occurs. The dorsal stripe is usually distinct from the background coloration but may occasionally blend into the background. The silvery dots that appear on the side of the body to the belly vary in density from scarce to compact. The top half of the iris is usually evenly golden but may occasionally include black blotches (Yoshikawa and Matsui 2013).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Japan

View distribution map in BerkeleyMapper.

To date, O. tsukubaensis has been found in the Tsukuba Mountains of eastern Honshu, Japan, on Mts. Tsukuba (the southern limit), Kinoko, Ashio, Kaba, and Tsubakuro (the northern limit) as well as in the nearby mountains of the Ibaraki Prefecture at elevations from 350 m to 871 m above sea level (Yoshikawa and Matsui 2013). Prior studies recorded this species as O. japonicus north of Mt. Tsubakuro in Saruda, Higashinaka-mura (currently Sakuragawa-shi; Sato 1943) and on Mts. Tomiya and Takamine (Kosuge 1979). Annual temperatures and amounts of winter precipitation are limiting factors on the ranges for many salamanders. Onychodactylus species prefer cold temperatures and need access to a stable network of plentiful underground streams for breeding. Compared to others in the O. japonicus species complex, O. tsukubaensis’ home range occurs at a relatively lower elevation. Selection pressures unique to this geographically isolated species, which occurs at a lower elevation, may account for the characteristics that differentiate this species from the others (Yoshikawa and Matsui 2013).

Life History, Abundance, Activity, and Special Behaviors
Onychodactylus tsukubaensis inhabits montane ecosystems at moderate elevations with dense forests on moist, cool, upland slopes below the timberline. Mating is thought to occur from the end of May to the middle of June in underground headstreams (about 550 - 700 meters above sea level), where the water level and temperature (7.9 - 9.5°C) remain stable annually (Yoshikawa and Matsui 2013). Mature adults have been observed gathering at the breeding sites from the end of April to mid-May (Hayase and Oseki 1983).

Nymphs, measuring roughly 35 mm in total length, appear in headstreams in March, scatter downstream, and grow and develop to about 80 mm in total length over a period of three years; metamorphosis occurs between July and October. Larvae may migrate back to their natal headstreams prior to or during metamorphosis as they are often found near the headstreams (Yoshikawa and Matsui 2013).

As a newly discovered species, the fecundity for this salamander is not yet known. A female specimen that was collected in the first week of May 2011 was kept in a completely dark environment in approximately 11°C water. Eighteen days later, she laid a pair of jellylike and spindle-shaped egg sacs. The total clutch size was 17 eggs, with 10 eggs in the larger sac, 6 in the second, and one fertilized egg left in the ovary. The eggs were entirely yellow and without pigment, ranged in diameter from 4.4 to 5.9 mm, and were organized in two rows upon being laid. After the bigger egg sac expanded, its eggs realigned into three rows. The egg sacs had a jellylike external layer that was elastic, yet so tough that it was hard to tear it apart by hand. The egg sacs were securely attached to a stone by short, jellylike stalks. The egg sac’s external layer had minor, lengthwise indentations (Yoshikawa and Matsui 2013).

Trends and Threats
Onychodactylus tsukubaensis is endemic to Japan with a very small home range that extends only over the top half of the Tsukuba Mountains. Currently, this salamander is abundant locally, but both its population and range size are declining due to habitat disturbance despite the fact that some populations are in protected land. The authors who described the species recommend that all habitats of this species be included as protected areas. The authors also express concern that the new identification of the species will make it a target for the pet trade, especially due to the proximity of the Tsukuba Mountains to urban areas and popular tourist locations (Yoshikawa and Matsui 2013).

No assessment has been made yet for O. tsukubaensis on the IUCN Red List and it is not currently listed in the Catalogue of Life.

Relation to Humans
This species is found in a highly urbanized area and thus has an increased potential of interacting with humans. This includes habitat disturbance via urbanization and pollution and illegal collection (Yoshikawa and Matsui 2013).

Possible reasons for amphibian decline

General habitat alteration and loss
Urbanization
Intentional mortality (over-harvesting, pet trade or collecting)

Comments
The species authority is: Yoshikawa, N. and M. Matsui. 2013. A new salamander of the genus Onychodactylus from Tsukuba Mountains, Eastern Honshu, Japan (Amphibia, Caudata, Hynobiidae). Current Herpetology. 32(1):9-25.

The specific name tsukubaensis refers to “Mount Tsukuba,” the type locality in the Tsukuba Mountains and also the highest mountain in the range in which this species has been found (Yoshikawa and Matsui 2013).

The Japanese name for this salamander is Tsukuba-hakone-sanshou-uwo (Yoshikawa and Matsui 2013).

Several cryptic species were once thought to be Onychodactylus japonicus. Allozymic studies for the O. japonicus species complex across its known home range have categorized it into six genetically distinct groups based on mitochondrial phylogeny: N-Tohoku, S-Tohoku, Tsukuba, SW-Honshu, Kinki, and Shikoku. Onychodactylus tsukubaensis was listed as the Tsukuba group or Clade II-B in prior studies; its sister group is the S-Tohoku group (Subclade II-A). These two groups are geographically separated and genetically very divergent (p-distance = 4.82 – 5.70%, mean = 5.23%), which may be due to O. tsukubaensis’ isolation since it occurs in geographically remote areas (Yoshikawa and Matsui 2013). The N-Tohoku group or Clade I has been described as the new species O. nipponoborealis, but the taxonomic status of the other groups has not yet been determined (Poyarkov et al. 2012).

References

Hayase, N., Oseki, K. (1983). ''Spawning and embryo of the salamander Onychodactylus japonicus (Houttuyn).'' Collecting and breeding, 45, 122-123.

Kosuge, T. (1979). Report of the 2nd National Survey on Natural Environment: Animal Distribution (Amphibians and Reptiles): Ibaraki Prefecture. Environmental Agency of Japan, Tokyo.

Poyarkov, N. A., Che, J., Min, M.-S., Kuro-o M., Yan, F., Li, C., Iizuka, K., and Vieites, D. R. (2012). ''Review of the systematics, morphology and distribution of Asian Clawed Salamanders, genus Onychodactylus (Amphibia, Caudata: Hynobiidae), with the description of four new species.'' Zootaxa, 3465, 1-106.

Sato, I. (1943). A Monograph of the Tailed Batrachians of Japan (In Japanese). Nippon Shuppan-Sha, Osaka, Japan.

Yoshikawa, N., Matsui M. (2013). ''A new salamander of the genus Onychodactylus from Tsukuba Mountains, Eastern Honshu, Japan (Amphibia, Caudata, Hynobiidae).'' Current Herpetology, 32(1), 9-25.

Species Account Citation: AmphibiaWeb 2013 Onychodactylus tsukubaensis: Tsukuba clawed salamander <https://amphibiaweb.org/species/7984> University of California, Berkeley, CA, USA. Accessed Nov 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Nov 2024.

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