Description
Microhyla pineticola, or the pine narrow-mouth frog, is a flattened frog with a leaf-like appearance. They have an adult male snout vent length of 17.2 – 19.5 mm and an adult female snout-vent length of 18.0 – 23.0 mm. The head is triangular shaped, with an approximately equal length and width. The snout is about a third of the length. Its nostrils are rounded, and located slightly closer to the tip of the snout than to the eyes. The canthus rostralis is sharp. The protuberant eyes have a diameter that is slightly shorter than the snout. The frog has no pineal spot. The tympanum is hidden, and a weak supratympanic fold runs from the corner of the eye to the arm. The lower arm is more than half the forelimb length. The prominent inner metacarpal tubercle is oval and the larger, single outer metacarpal is round and flattened. The frog’s fingers are slender and have no webbing in between digits. The relative finger lengths are I < II < IV < III. All the fingers have discs with narrow, dorsal peripheral grooves while fingers II, III, IV have an additional medial groove. The relative disc width formula is I < IV < II < III. There is one prominent, round subarticular tubercle on fingers I and II and two on fingers III and IV. No nuptial pads were found. The slender hind limbs are longer than the snout-vent length. When adpressed along the body, the tibiotarsal articulation extends between the nostril and the snout tip. The tibia is slightly shorter than the foot. The prominent inner metatarsal tubercle is large, elongated, and oval. It is slightly less than half the length of the first toe. The distinct outer metatarsal tubercle is rounded, elevated, and slightly smaller than the inner metatarsal tubercle. The relative toe lengths are I < II < V < III < IV. The toe tips expand into discs. Webbing is present between the toes, but is poorly developed with a formula of I 1 ½ – 2 ½ II 1 ¾ – 3 III 2 ¾ – 3 ¾ IV 4 – 2 ½ V. The subarticular tubercles on the toes are similar to those on the fingers, but smaller with a formula of 1, 1, 2, 3, 2. The skin is smooth, with a few tubercles present on the posterior dorsum, and along the dorsolateral sides of the frog (Poyarkov et al. 2014).

The species description includes the description of 10 tadpoles between the stages of 25 and 37. Individuals between the stages of 25 - 27 had total lengths of 12.2 - 18.2 mm, body lengths between 4.8 - 6.1 mm, and tail lengths between 7.4 - 12.1 mm. At stages 28 - 29, total lengths were between 19.0 - 19.8 mm, body lengths between 6.2 - 6.4 mm, and tail lengths between 12.8 - 13.4 mm. Between stages 34 - 37, total lengths were between 21.5 - 24.0 mm, body lengths between 7.2. - 8.0 mm, and tail lengths between 14.3 - 16.0 mm. In the dorsal view, the body is elliptical or pear-shaped with the head being wider than the body. From the lateral view, the body is triangular with a flat dorsal surface and rounded ventral surface. The snout is rounded, and the head of the tadpole is larger than the stomach. The large, bulging eyes are positioned laterally with pupils that are oriented laterally and somewhat ventrally. They are visible from the ventral view. Tadpoles have no beaks, nostril openings, nor discernible lateral line system observed in the life stages samples from. Oral disks are present as a funnel, directed dorsally. The upper labium is thick with prominent round lobes at the corners of the mouth. The lower labium is umbrella shaped with semicircular marginal ridges. The infralabial flange is horse-shoe shaped and has several prominent papillae. They possess free spiracles that form an elongated membrane, are positioned medially, and end at the stomach. The almost vertical vent tube opens, medially, at the junction of the lower fin. The tails are almost twice as long as the body, with a muscular portion at the tail base and a thin filament-like tip. The base of the tail musculature is equal in height to the lower fin. The upper fin does not extend onto the body. The upper fin reaches its maximum height at the second third of the tail while the lower fin reaches its maximum height in the first third and is taller than the upper fin (Poyarkov et al. 2014).

DIAGNOSIS:

The Microhyla genus is one of the most taxonomically challenging groups of asian frogs but species can be differentiated with a combination of various characteristics. Due to the large list of similar species, only a sample of similar species are discussed below. Among all Microhyla, the species most similar to M. pineticola is the M. heymonsi, however, M. pineticola can be differentiated by having a deeply free tongue, a hand with two low palmar tubercles, and comparatively much longer hindlimbs than M. heymonsi, a snout that is clearly acuminate in profile, and a tibiotarsal articulation of the adpressed hind limb that usually extends beyond the snout. Among other species, the smooth dorsal skin in M. pineticola is opposed to the warty skin present in M. annamensis. The presence of basal rudimentary webbing between toe II and toe III and smaller body size differentiates M. pineticola from M. berdmorei. And a reduced first finger, and dorsal coloration pattern differentiates M. pineticola from M. butleri (Poyarkov et al. 2014).

Larval M. pineticola is superficially similar to M. heymonsi, but can be differentiated because M. pineticola is less elongated and more pear-shaped than M. heymonsi. Additionally, the mouth part of M. heymonsi extends beyond the head, the lobed shape has a rostromedial notch, and the oral disc is half the body width while in M. pineticola the mouth does not extend, there is no notch and the oral disc is a third of the body width. Lastly, the round bulges at the angles in the mouth are more developed and distinct in M. pineticola than in M. heymonsi (Poyarkov et al. 2014).

COLORATION:

In life, the dorsum of M. pineticola is pinkish brown, with a distinct dark wood-grain pattern that runs across the head, eyelids, and continues horizontally down its sides. These dark bands diverge and connect towards each other at the groin area. More specifically, there is a distinct brown, triangular interorbital bar. There is darker coloration on the back of the head, slightly behind the eyes, and in the groin area, left of the medial line. At the ends of the appendages the main brown coloration fades to white. The ventrum is cream-white, with indistinct light-brown and beige marbling toward the midline of the ventrum. This paler pigmentation at the tips of digitals matches the pale, cream-colored underside of the frog as well (Poyarkov et al. 2014).

In preservative, the colors are slightly faded. Red and pink tints are especially faded, and the yellow from sides turns more cream colored (Poyarkov et al. 2014).

VARIATION:

Variations between members of this species primarily exist with size and body proportions. Females (18.0 - 23.0 mm) are larger in snout-vent length than males (17.2 - 19.5 mm), and males possess slit-like openings for singular vocal sacs. Males also show slightly different coloration patterns on their head, and may possess extra patterns, such as a large, butterfly-shape brown pattern on the dorsum, or a thin white stripe along the midline of the dorsum (Poyarkov et al. 2014).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Viet Nam

View distribution map in BerkeleyMapper.

Though not well dispersed, M. pineticola is endemic to the southern part of the Annamite Mountains in southern Vietnam in the provinces of Lâm Đồng and Đắk Lắk. The frogs dwell in mixed montane tropical forest with a predominance of pine species at elevations of about 860 - 1850 m (Poyarkov et al. 2014).

Life History, Abundance, Activity, and Special Behaviors
Microhyla pineticola can be found on the ground, both during the day and at night (Poyarkov et al. 2014).

Microhyla pineticola have hidden tympanum in addition to a vocal sac. This body structure suggests that calling may be a breeding behavior for this species (Poyarkov et al. 2014).

Microhyla pineticol are associated with water bodies at high elevations. Late staged tadpoles were found in pools during mid-July. As a result, it can be assumed that their breeding season coincides with warm, and wet environmental conditions (Poyarkov et al. 2014).

It is assumed that the M. pineticola have similar clutch sizes as other closely related Microhyla species, with several tens of eggs. Although no eggs of M. pineticola have been observed, eggs of another member in the species group, M. minuta, have a diameter that ranges from 0.78 - 1.2 mm, and it takes approximately 47 - 48 hours for the tadpoles to hatch (Poyarkov et al. 2014).

Other amphibians found in sympatry include Ingerophrynus galeatus, Microhyla annamensis, and Rhacophorus vampyrus. Other tadpoles found near the breeding sites of M. pineticola are Feihyla palpebralis and Polypedates megacephalus (Poyarkov et al. 2014).

Trends and Threats
Due to the fact that the M. pineticola are found in a small habitat range in Vietnam, human impacts on the M. pineticola’s habitat have far-reaching consequences. Part of the species habitat is protected, such as in Bidoup – Nui Ba National Park of Lam Dong Province and the Chu Yang Sin National park of Dak Lak Province. However, habitat loss outside of these provinces due to logging, destruction of forests, agricultural activity, road construction, and other anthropogenic activities are still a threat. These threats are likely associated with the decreasing population trend of this species (Poyarkov et al. 2014, IUCN 2017).

Comments

PHYLOGENETIC RELATIONSHIPS:

Maximum Likelihood and Bayesian Inference analyses of 12SrRNA, tRNA-Val and 16S rRNA gene fragments indicate that M. pineticola is part of the Microhyla achatina group. More specifically, M. pineticola is sister to M. neglecta and together they are sister to M. heymonsi (Pokaryov et al. 2020).

ETYMOLOGY

The species epithet, “pineticola” is derived from the latin word “pinetum” which means “inhabitants of pine forests”. This name was specifically made because the species mainly inhabited the pine forests of the Langbian Plateau and because of the characteristic dorsal pattern that was commonly seen in the females, which resembled the grain of pinewood (Poyarkov et al. 2014).

References

IUCN SSC Amphibian Specialist Group. (2017). "Microhyla pineticola." The IUCN Red List of Threatened Species 2017: e.T73727759A73728084. https://dx.doi.org/10.2305/IUCN.UK.2017-2.RLTS.T73727759A73728084.en. Downloaded on 19 February 2021.

Poyarkov, Jr, N.A., Vassilieva, A.B., Orlov, N.L., Galoyan, E.A., Dao, T.T.A., Le, D.T.T., Kretova, V.D., Geissler, P. (2014). ''Taxonomy and distribution of narrow-mouth frogs of the genus Microhyla Tschudi, 1838 (Anura: Microhylidae) from Vietnam with descriptions of five new species.'' Russian Journal of Herpetology, 21(2), 89-148. [link]

Poyarkov, N. A., Nguyen, T. V., Trofimets, A. V., Gorin, V. A. (2020). “A new cryptic species of the genus Microhyla (Amphibia:Microhylidae) from Langbian Plateau, Vietnam.” Taprobanica, 9, 136-163. [link]

Species Account Citation: AmphibiaWeb 2022 Microhyla pineticola: Pine (pigmy) narrow-mouth frog; Nhai bau Thong (Vietnamese) <https://amphibiaweb.org/species/8219> 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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