Description

Oreolalax sterlingae is a relatively small Megophryide frog described from one male and one female specimen that have snout-vent lengths of 37 mm and 45 mm, respectively. The head has a protruding snout, distinct canthus rostralis, and concave loreal region. The nostrils are located between the tip of the snout and the eye. The pupil is vertical. Behind the eye, the tympanum is hidden, but the parotoid gland is obvious and elongated. The forelimbs are uniquely enlarged and comparatively shorter. The fingers have round tips, and lack dermal fringes and webbings. The male has nuptial spines on fingers I and II. The tibia is shorter than the femur, and the foot is long with thin, long, and round-tipped toes. Webbing is only present at the base of the toes. The subarticular tubercles are distinct in O. sterlingae. It does not have outer metatarsal tubercle or tarsal folds, but does have an undeveloped inner metatarsal tubercle. There are round spiny warts on the dorsum, and, in males, a smaller patch of spines on chest (Nguyen et al. 2013).

The tadpoles have ovoid bodies, a rounded snout, a left-directing spiracle, and dorsally positioned eyes (Rowley et al. 2017).

DIAGNOSIS:

Oreolalax sterlingae is smaller relative to all other species in genus Oreolalax, and only has webbing at the base of the toes compared to the fully webbed O. granulosus and O. weigoldi, and nearly fully webbed O. xiangchengensis. The tympanum is hidden in O. sterlingae, but obvious in O. rhodostigmatus. Oreolalax sterlingae has uniquely round spiny warts on the dorsum, and smaller spinal patches on chest that distinguish it from O. granulosus, O. jingdongensis, O. liangbeiensis, O. major, O. multipunctatus, O. nanjiangensis, and O. popei. There is dark marbling on O. sterlingae’s belly and limbs, while O. liangbeiensis, O. nanjiangensis, O. pingii, O. puxiongensis, and O. schmidti lack markings. Moreover, O. sterlingae’s belly is smooth rather than grainly as in O. weigoldi. White spots appear on the flanks of O. sterlingae, but are not present in O. chuanbeiensis, O. granulosus, O. major, O. multipunctatus, O. nanjiangensis, O. omeimontis, and O. popei. There is no dark triangular pattern on the interorbital region of O. sterlingae, but one is present in O. omeimontis, O. puxiongensis, and O. schmidti. Three dark bars are present on the upper thigh of O. sterlingae, but absent in O. pingii (Nguyen et al. 2013).

The tadpole of O. sterlingae is smaller than all the related species in the genus Oreolalax, but it resembles O. granulosus in black coloration (Rowley et al. 2017).

COLORATION:

Live O. sterlingae have a brown dorsum with small black spines and cream venter with brown mottling. Whitish spots are present on the lip and limbs, and yellowish-white spots are present on the lower flanks. In preservative, O. sterlingae’s brown fades into grayish brown, but otherwise, colors do not change much (Nguyen et al. 2013).

The tadpoles have black bodies and pale tail fins that are clear with a gold stripe running anteriorly on both the upper and lower margins (Rowley et al. 2017).

VARIATION:

There is some sexual dimorphism in this species. The male has black spines on the lower lip, small spinal patches on the chest, and nuptial spines on fingers I and II, while the female has less prominent warts (Nguyen et al. 2013).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Viet Nam

View distribution map in BerkeleyMapper.

Oreolalax sterlingae is endemic to Hoang Lien Mountain Range in northern Vietnam. It was first discovered in a small, rocky stream in the bamboo forest at an elevation of 2900 m above sea level at Mount Fansipan (Nguyen et al. 2013; Tapley et al. 2020). Subsequent surveys in 2016 and 2017 found O. sterlingae on the summit of Mount Fansipan and in rocky streams at lower elevations than the type locality. In 2018, O. sterlingae tadpoles were detected in a 2 m wide stream in the evergreen forest at Mount Pu Ta Leng, 20 km northeast of the type locality. According to the known records, researchers suggest the species ranges in elevation from 2344 m to 3108 m above sea level and has an Extent of Occurrence of 639 km² (Tapley et al. 2020).

Life History, Abundance, Activity, and Special Behaviors

Type specimens of O. sterlingae were collected at night, but it is unclear if this species is nocturnal or diurnal (Nguyen et al. 2013).

Oreolalax sterlingae is noted as being locally abundant, but the population is expected to be small and decreasing due to its small Extent of Occurrence and increasing threats (IUCN 2015).

Adult O. sterlingae live near rocky streams and rivulets in bamboo forests, where they experience heavy precipitation in a temperature range of -3 to 20 degrees celsius (Nguyen et al. 2013; IUCN 2015).

Oreolalax sterlingae is assumed to be ovoviviparous and have indirect development like other members of the genus Oreolalax (IUCN 2015).

Oreolalax sterlingae has no vocal sac, and no call has been recorded (Nguyen et al. 2013).

A female (paratype) was documented with yellow eggs (3.6 mm in diameter) in the body (Nguyen et al. 2013).

Tadpoles are aquatic and can be observed year-round in large pools of rocky streams (Tapley et al. 2020). They are bottom dwellers that prefer actively flowing water (Rowley et al. 2017).

Trends and Threats
Known sites of O. sterlingae occurrence are covered by Hoang Lien National Park and Bat Xat Nature Reserve. Unfortunately, they are not fully protected from human disturbance. Disturbance is most severe at the type locality in Hoang Lien National Park, where the stream is polluted by garbage and runoff from a campsite and toilet, and a fraction of the stream bed has been destroyed for gravel mining. Oreolalax sterlingae habitat on the summit of Mount Fansipan is fragmented by cable car construction and associated infrastructure development for tourism. In lower elevation, hiker activity could have a potential impact on O. sterlingae. Compared to Hoang Lien National Park, Bat Xat Nature Reserve is relatively intact with good forest cover (Tapley et al. 2020). In the future, climate change is predicted to increase water stress in tropical montane forests, which would threaten the survival of this water-dependent species, and as a high-elevation species, any O. sterlingae forced to undergo climate-induced migration would have a hard time finding new habitat with suitable climate (Foster 2001). IUCN (2015) suspects the population of O. sterlingae is decreasing given the threat it faces, but further research is needed to understand the exact population size and trend (Tapley et al. 2020).

Relation to Humans
Oreolalax sterlingae is not known to be collected for food, pet trade, or traditional medicine. Unsustainable and irresponsible tourism is blamed for degrading the habitat of O. sterlingae in Hoang Lien National Park (Tapley et al. 2020).

Possible reasons for amphibian decline

General habitat alteration and loss
Mining
Habitat fragmentation
Local pesticides, fertilizers, and pollutants
Climate change, increased UVB or increased sensitivity to it, etc.

Comments

PHYLOGENETIC RELATIONSHIPS:

Both Maximum Parsimony and Bayesian Inference analyses of mitochondrial genes 12S and 16S show that O. sterlingae is a unique member of the genus Oreolalax. More specifically, O. sterlingae is sister to the clade containing O. chuanbeiensis, O. multipunctatus, O. nanjiangensis, O. omeimontis, and O. popei (Nguyen et al. 2013). However, this placement is not strongly supported by either analysis. More information from both mitochondrial and nuclear genes is needed to provide a more solid placement (Nguyen et al. 2013).

ETYMOLOGY:

The specific epithet “sterlingae” refers to Dr. Eleanor J. Sterling from the American Museum of Natural History in New York, in recognition of her exceptional contribution to biodiversity research and conservation in Vietnam, where the species is found (Nguyen et al. 2013).

OTHER INTERESTING INFORMATION:

Oreolalax sterlingae was the first species from the genus Oreolalax that was described outside of China (Nguyen et al. 2013).

References

Foster, P. (2001). “The potential negative impacts of global climate change on tropical montane cloud forests.” Earth-Science Reviews, 55 (1-2), 73-106. [link]

IUCN SSC Amphibian Specialist Group. (2015). "Oreolalax sterlingae." The IUCN Red List of Threatened Species 2015: e.T76491633A76491638. https://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T76491633A76491638.en. Downloaded on 16 February 2021.

Nguyen, T. Q., Phung, T. M., Le, M. D., Ziegler, T., Böhme, W. (2013). “First record of the genus Oreolalax (Anura: Megophryidae) from Vietnam with description of a new species.” Copeia, 2(2), 213-222. [link]

Rowley, J. J. L., Tapley, B., Chung, N. T., Altig, R. (2017). “Tadpole of the critically endangered Sterling’s toothed toad (Oreolalax sterlingae).” Zootaxa, 4272(4), 579-582. [link]

Tapley, B., Nguyen, L. T., Portway, C., Cutajar, T., Nguyen, C. T., Luong, H. V., Kane, D., Harding, L., Rowley, J. J. L. (2020). “A point endemic no more; a range extension for Oreolalax sterlingae (Nguyen et al., 2013) in Bat Xat District, Lao Cai Province, northern Vietnam.” Herpetology Notes, 13, 497-500. [link]

Species Account Citation: AmphibiaWeb 2022 Oreolalax sterlingae: Sterling's Toothed Toad <https://amphibiaweb.org/species/8524> University of California, Berkeley, CA, USA. Accessed Dec 21, 2024.

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

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