Pachytriton labiatus (Unterstein, 1930)
Unterstein's Newt (English), Spotless Stout Newt, Pingchi's Newt
The species is abundant in its range. Zhao et al. (1994) compared the number of animals collected in 1986 and 1993, and found no sign of population decline. However, large numbers of wild-caught animals appear in the pet trade every year. Local inhabitants may sell them as juvenile giant Chinese salamanders (Andrias davidianus; Xu et al., 2002). Human exploitation and habitat destruction are the two most important factors affecting P. labiatus. It is listed as of least concern by IUCN (2010).
Large-bodied newt with smooth skin. Color of the back uniform brown, sometimes with red spots or dorso-lateral orange stripes. No small black spots on body, head and tail. Distinct red and black coloration of the belly.
2n=24, 1M, 2M, 3M, 4M, 5M, 6M, 7SM, 8M, 9M, 10SM, 11SM, 12M, from Gu & Tian (2000). (M: metacentric; SM: submetacentric)
The mitochondrial and nuclear DNA data are available from Wu et al. (2010).
Coloration of P. labiatus is nearly identical to that of P. brevipes from Zhejiang, Anhui, Guangdong and eastern Guangxi, which also have a uniformly dark brown to black dorsum. This is a case of convergent evolution of color pattern (Wu et al., 2010). Sometimes it is extremely difficult to diagnose species based on external morphology alone.
A moderate to large newt. The morphology and size are similar to P. brevipes, it may even be bigger. Males are significantly smaller and weigh less than females (Xu et al., 2002). Tail is shorter than snout-vent length. Head is flat, and the trunk is stout and robust. Snout is very broad in some populations, so the head almost gets a rectangular shape. Eyes are small, located at or anterior to the jaw angle. Labial folds are more conspicuous on the upper jaw than the lower jaw. Two lines of vomerine teeth orient in a Λ-shaped manner, converging anteriorly. Gular fold is present and paratoid region is evident. There is no vertebral ridge, but a vertebral groove may be present (Fei et al., 2006). The skin is very smooth and slippery due to secretion of mucus. Limbs are relatively short. When forelimb and hindlimb are adpressed, toes and digits never meet. Digits are short and partially webbed. The lengths of fingers are 3 > 2 > 4 > 1, and the lengths of toes are 3 > 4 > 2 > 5 > 1. The anterior part of the tail is rounded, and the posterior part is laterally compressed like a paddle (hence their other popular name: paddle tail newt). Sexually mature males have papillae at the cloaca.
Live animals are uniformly brown to dark brown on the dorsal side, and lack the black dots that characterize most P. brevipes populations. Some P. labiatus develop two dorsolateral lines of red flecks. Orange blotches are present on the ventral side, which are well defined in juveniles, blurred in subadults, and finally washed out in aged animals (Wu et al., 2010). After preservation, the orange or red coloration turns to ivory white. No pattern difference is found between males and females. Larvae are grey on the back and white on the ventral side (Zhao et al., 1994). A fully metamorphosed juvenile is about 70 to 80 mm, it is sexually mature at 125 mm (Fei et al., 2006).
All measurements are from Fei et al. (2006).
Male (10 specimens). Total length: 153.3–191.5 mm; snout-vent length: 82–108 mm; head length: 21.2–26.9 mm; head width: 16.9–23.3 mm; forelimb length: 16.3–20.6 mm; hind-limb length: 18–26.5 mm.
Female (10 specimens). Total length: 168–198 mm; snout-vent length: 95.5–106 mm; head length: 23.7–27.7 mm; head width: 18.3–24 mm; forelimb length: 18.4–22 mm; hind-limb length: 19.6–23.4 mm.
Ecology and Distribution
Two allopatric distributions were recorded in southern China: one range includes Guizhou, Hunan, Guangxi and Guangdong and the other includes Anhui, Zhejiang and probably Jiangxi (Zhao & Hu, 1988; Fei et al., 2006). Recent molecular work suggests that only animals from Hunan, Guizhou and Guangxi (excluding populations close to Guangdong) are real P. labiatus (Wu et al., 2010; Wu et al., unpublished). Animals from Guangdong, eastern Guangxi, Anhui and Zhejiang are genetically identified as P. brevipes.
Pachytriton labiatus inhabits mountain streams at various altitudes. Some streams are several meters wide and about one meter deep, whereas others are mere trickles of 20 to 40 cm deep. Substrate includes sand and small rocks. Water can be either clear or extremely murky (due to flooding). The species is fully aquatic. Populations in Hunan Province hibernate from November till April in crevices or under boulders where water is present (Zhao et al., 1994). The newts hide in shelters during daytime, and are active at night. Pachytriton labiatus feeds on earthworms, other aquatic arthropods and insect larvae. Two animals were observed fighting for the same earthworm from the two ends. After their snouts met, they rolled rapidly like a crocodile’s death roll (Wu, Y. pers. comm.). When captured, the animal may emanate a strong sulfurate odor (Fei et al., 2006). It may also emit food from the stomach. Zhao et al. (1994) recorded anti-predator postures including stretching of limbs, lifting the head and tail, and exposing the orange ventral blotches.
The breeding season typically begins in April and lasts to July (Fei et al., 2006). The courtship behaviors of some Pachytriton from the pet trade were observed by Sparreboom & Thiesmeier (1999). Although those animals are mostly likely P. brevipes from Zhejiang, the observation still provides insight in courtship behaviors of this genus. When a male senses the presence of a female, he swims toward her immediately and tries to block her path. Then the male positions itself perpendicular to the female’s body, slowly fanning his tail tip near her snout. The female may either swim away or stay motionless if she is interested. After several bouts of tail-fanning, she moves towards the male, who turns around and begins to retreat. The female touches the male’s tail while following. Finally, the male deposits a spermatophore and the female creeping behind him picks it up with her cloaca.
Females lay around 40 single eggs at the lower surface of rocks in streams; sometimes the eggs are clustered to form a patch (Zhao et al., 1994). The ovum is milky white and attains 3 to 4 mm in diameter. There are three jelly capsules enclosing the ovum, so the egg is about 10 mm in diameter.
Evolution and Systematics
According to current taxonomy, Pachytriton labiatus and P. brevipes are mainly distinguished by their coloration (Fei et al., 2006). However, a homoplastic color pattern may lead to misidentification of P. brevipes from Zhejiang, Anhui, Guangdong and eastern Guangxi as P. labiatus (Wu et al., 2010). Pachytriton labiatus is the sister species to the group of P. brevipes and P. archospotus. The taxonomy of Pachytriton is subject of debate.
- Molge labiatum Unterstein, 1930, Sitzungsber. Ges. Naturforsch. Freunde Berlin, 1930: 313. (synonym)
- Pachytriton granulosus Chang, 1933, Contrib. Biol. Lab. Sci. Soc., China, Zool. Ser., 9: 320. (synonym)
- Pingia granulosa Chang, 1935, Bull. Soc. Zool. France, 60: 425. (synonym)
- Pachytriton brevipes labiatus Hu, Zhao, and Liu, 1973, Acta Zool. Sinica, 19: 149&ndash. 178. (synonym)
- Hypselotriton (Pingia) granulosus Dubois and Raffaëlli, 2009, Alytes, 26: 32, 46, 65. (synonym)