Hynobius formosanus Maki, 1922
Distribution is very local and populations are small, making this as well as the other Taiwanese Hynobius species vulnerable to habitat destruction and degradation, due to development of infrastructure for tourism. Hynobius sonani and H. formosanus were first protected under the Cultural Heritage Preservation Law in 1986 as precious and rare species, and later by the Wildlife Conservation Law (1989) (Lee et al., 2006). Both species are considered critically endangered by Zhao (1998) and are listed as endangered by Stuart et al. (2008) and IUCN (2010). Currently all five salamander species in Taiwan are protected by the Wildlife Conservation Law.
Shorter than other Taiwanese species except Hynobius fuca, around 10 cm in total length (Lai & Lue, 2008). The interior line of vomerine teeth is very long, exceeding the posterior margin of eye (Fei et al., 2006). 11 to 12 costal grooves (Lai & Lue, 2008). Most specimens have four toes on hind limb. Tail stout and short. Tail tip pointed. Dorsal color is yellowish brown with irregular dark blotches or vice versa (i.e., dark brown with yellow to golden blotches). Venter has dark small spots (Fei et al., 2006).
Karyotype:
2n=58, 1M, 2M, 3M, 4ST, 5SM, 6M, 7M, 8SM, 9M, 10ST, 11SM, 12SM, 13M, 14M, 15M, 16M, 17M, 18M, m (19–29), from Iizuka et al. (1989).
M: metacentric; SM: submetacentric; T: telocentric; ST: subtelocentric; m: micro-chromosome
The mitochondrial genome has been sequenced by Zhang et al. (2006).
Hynobius formosanus resembles H. fuca in overall size and having four toes and relatively short tail and limbs. But the former species has brown blotches on the dorsum and the latter has none (Lai & Lue, 2008).
Tail shorter than snout-vent length. Head round, flattened; nostril nearer tip of snout than eye; distance between nares greater than between eyelids; eyelid equal to interorbital space; 11–12 costal grooves. Vomerine tooth row equals 3/4 width of tongue; interior rows close together. Gular fold present. Behind the eye, a horizontal groove crosses over the gular fold. A vertebral groove present at the middle line of the dorsum. Big round black eyes. Paratoids large and flat. Tail cylindrical, slightly compressed toward the tip, which is blunt. Limbs rather short, fore and hind limbs do not touch when laid against the body. Fifth toe smaller than first (Maki, 1922; Dunn, 1923). But Iizuka et al. (1989) and Lai & Lue (2008) observe only four toes in this species. Tubercles are not noticeable on palms and soles (Fei et al., 2006). Skin smooth. Tail is longer in males than in females and more males than females appear to have 11 rather than 12 costal grooves (Lai & Lue, 2008). Color variable, tawny yellow background, mottled with irregular, sometimes dense brown spots and patches over body and tail, small spots on belly. Total length 9-10 cm (Lai & Lue, 2008).
All measurements are from Lai & Lue (2008).
Male (15 specimens). Snout-vent length: 47–61.7 mm; Tail length: 31.6–46.1 mm; Head length: 8.8–13.6 mm; Head width: 7.6–9.6 mm; forelimb length: 10.3–13.8 mm; hind-limb length: 11.6–14.7 mm.
Female (8 specimens). Snout-vent length: 46.4–56.7 mm; Tail length: 30.8–38.1 mm; Head length: 8.2–12.6 mm; Head width: 7.3–9.2 mm; forelimb length: 10.6–12 mm; hind-limb length: 12–15.6 mm.
Based on mitochondrial data, Hynobius formosanus, H. glacialis and the group of H. sonani and H. arisanensis form a well-supported trichotomy. But relationships among the three lineages are not known (Lai & Lue, 2008).
Hynobius formosanus occurs from the Central Mountain Range to the northern Central and to the Syueshan Mountain ranges of Taiwan, at elevations from 2,300 to 2,900 m. It is partly sympatric with H. sonani (between Mt. Hohuan and Mt. Bilu); H. formosanus and H. glacialis are parapatric, with the former at lower elevations and latter at higher ranges (Lai & Lue, 2008; Chang, 2010).
The species, like the other Taiwanese Hynobius species, occurs in high-elevation montane areas, in woodlands, and broadleaf and coniferous forests, and the transition zone between coniferous forests and alpine bamboo grasslands (Lai & Lue, 2008): Areas with low temperatures, high annual precipitation, little disturbance and high humidity. The animals spend most of their lives under logs and rocks near small cool creeks and seepage areas with moist substrate. Adult salamanders usually search for food actively at night under debris on the forest floor and prey mainly on sow bugs, earth worms, and other terrestrial invertebrates. Their natural enemies are snakes and other predators (see refs in Lee et al., 2006).
The breeding season ranges from November to January, when the amount of rainfall is small (Kakegawa et al., 1989). Eggs are laid in headwater streams and underground seepages. Male and female adults and freshly laid egg sacs were found in February in a small water reservoir under stones, water temperature 1°C, along a mountain path. Some adults showed biting wounds, probably the result of agonistic encounters (2008, MS pers. obs.). The female produces a pair of string-like egg sacs, containing some 14–15 large eggs (4.25 mm diameter). Egg sacs are laid in small slow-moving bodies of water (Lee et al., 2006), where they are attached under stones (Kakegawa et al., 1989). The egg sac is transparent, outer envelope not tough as in H. sonani, with many irregular horizontal grooves and lighter longitudinal stripes than in H. sonani. Color not uniform, but generally light yellowish with a brown tint, the brown fading with development of the embryos. At a water temperature of 7–9°C embryos hatch some three months after oviposition. Larvae hatch at a total length of some 19–21 mm, retaining a large amount of yolk; they have no balancers. Larvae are reported to take almost no food; metamorphosis takes place about two months after hatching at a length of 25 mm (Kakegawa et al., 1989).