Hynobius amjiensis Gu, 1992
Listed as critically endangered in the IUCN Red List of Threatened Species (IUCN, 2010). Zhao (1998) also places Hynobius amjiensis on the red list of endangered Chinese amphibians. This salamander is only found at the type locality, which is a small swamp at the top of a mountain. Gu et al. (1999) report population dynamics from the type locality monitored between 1992 and 1998 as follows. Population size shows sign of decline. Less than 400 females reproduce each year. Ponds for reproduction are decreasing in size since 1990 because rocks and soil are washed into ponds by rain due to deforestation. Illegal collection further reduces the population size. Therefore, immediate measures should be taken to protect this salamander.
Vomerine teeth lined in “ɿɾ” shape: interior line extends posteriorly to the posterior margin of eye. Thirteen costal grooves. Tail length slight shorter than snout-vent length. When limbs are adpressed, fingers and toes overlap.
Karyotype:
2n=56, 1M, 2SM, 3SM, 4ST, 5M, 6M, 7ST, 8SM, 9M, 10SM, 11SM, 12SM, 13M, 14M, 15M, 16M, 17M, 18M, m (19–28), from Zeng et al. (1997)
M: metacentric; SM: submetacentric; T: telocentric; ST: subtelocentric; m: micro-chromosome
The mitochondrial genome has been sequenced by Zhang et al. (2006).
This salamander looks similar to Hynobius yiwuensis but has a larger body size (150–160 mm in total length), a relatively longer tail (90% of snout-vent length) and 13 costal grooves. Hynobius yiwuensis is smaller (80–120 mm) with a shorter tail (60–75% of snout-vent length) and typically 10 costal grooves (Fei et al., 2006).
This description is based on the original description by Gu (1992) and additional information from Fei et al. (2006). Trunk stocky and somewhat flattened. 13 costal grooves. Head oval and slightly flattened. Head a little longer than wide, snout obtuse and rounded. Distance between nostrils less than or equal to distance between eyes. Eye diameter less than distance between eyes, pupil round. No labial fold. Vomerine teeth lined in “ɿɾ” shape: interior line extends posteriorly to the posterior margin of eye and converges but not contacts at the middle axis. Tongue oval, adhering to bottom of oral cavity. Tail long, a little shorter than snout-vent length. Tail base almost round, flattened laterally towards the tip. Low dorsal tail fin, tail tip obtuse and rounded. Limbs slender, forelimbs shorter and weaker than hind limbs. Fingers and toes overlap when limbs are laid against the body. Horny cover absent on palms, tarsa and tips of all digits. Tubercles are prominent at palms and tarsa. Webbing is absent. Skin smooth, central groove running along the dorsum. Gular fold prominent. Vent of males is a longitudinal groove with an anterior papilla. Color dusty gray or sepia above, dark gray brown below.
All measurements are from Gu (1992).
Male (17 specimens). Total length: 153.3–166 mm; snout-vent length: 79.5–86.5 mm; Head length: 17–21.2 mm; Head width: 15.5–19 mm; forelimb length: 23.5–26 mm; hind-limb length: 27.8–29.5 mm.
Female (1 specimen). Total length: 166 mm; snout-vent length: 84.5 mm; Head length: 18.7 mm; Head width: 19 mm; forelimb length: 24 mm; hind-limb length: 28.2 mm.
By analyzing allozyme and mitochondrial data, Fu et al. (2003b) reveal a high inbreeding coefficient in Hynobius amjiensis from the type locality. They also suggest a sister relationship between H. amjiensis and H. yiwuensis, which occurs geographically close to the former species. A recent molecular study includes all species of Hynobius from continental China (Nishikawa et al., 2010). This work indicates that H. yiwuensis is the most basal species from continental China, and H. amjiensis is the sister to H. maoershanensis, H. chinensis and H. guabangshanensis.
This species is only known from the type locality at the top of Mount Longwang in northern Zhejiang province. The adjacent Mount Tianmu could harbor some populations too.
The salamander occurs in a marshy area, covered with spaghnum mosses at 1,300 m altitude. This narrow area is surrounded by mountain tops that are only 50–100 m higher. There are nine small deserted ponds that are dug for previous geological work and have now become the only breeding sites for Hynobius amjiensis (Gu, 1992). All ponds are around 1 m long, 1 m wide and less than 1 m deep (Gu, 1992). Ponds are surrounded by mosses, grasses, pine and deciduous woods and shrubs. Outside the breeding season H. amjiensis is a terrestrial species, hard to find. The salamander feeds on small aquatic invertebrates and earthworms (Gu, 1992). When food is scarce, cannibalism occurs (Fu et al., 2003a). In the laboratory, all small larvae are eaten by ones that are twice as large when food is scarce and larval density is high. The extent of cannibalism is positively correlated with the size difference among larvae.
Breeding season lasts from late November to late March (Gu, 1992). Egg sacs and males are found in ponds under ice in late December. More eggs are found in February, which could be the reproductive peak. Females leave ponds soon after eggs are laid. Egg sacs are laid in pairs with one end attaching to aquatic plants, underwater twigs or stones. The egg sac is 460–580 mm in length, 27–37 mm in diameter. Each sac contains 43–77 eggs. Less than 1% of eggs survive to juvenile stage due to low water oxygen level and scarce food supply given the conditions of these lentic ponds (Gu et al., 1999).