Description
Leptolalax pallidus is a smaller frog with a male snout-vent length range of 24.5 – 27.7 mm. No females were described in the original description. The width of the head is only slightly shorter than the length of the head. In the dorsal view the snout is truncate and in the profile it projects a little over the lower jaw. The nostrils are closer to the snout than the eyes. The canthus rostralis is gently rounded but indistinct. The loreal region slopes. The eye diameter is smaller than the snout length, and the pupils are vertical. The indistinct, round tympanum has diameter that is smaller than the eye diameter. The rim of the tympanum is a slightly raised and a distinct supratympanic ridge runs from the eye to the axillary gland. The fingertips are rounded, slightly swollen, and have relative lengths of I < IV < II < III. Only one subarticular, located at the base of finger IV, can be found and the fingers lack webbing and dermal fringes. Nuptial pads were not found on males. The length of the tibia is slightly over half of the snout-vent length of the frog. When extended, the tibiotarsal articulation reaches the anterior edge of the eye. Near the knee, on the posteroventral surface of the thigh is an oval femoral gland. The toes are similar in appearance to the fingers and the relative toe lengths are I < II < V < III < IV. The toes have rudimentary webbing and dermal ridges have replaced the subarticular tubercles at the base of toes II and III. Lateral fringes are absent. While the outer metatarsal tubercle is absent, there is a large, oval inner metatarsal tubercle. The dorsum is shagreened in life but becomes less tubercated in preservative. The ventrum is smooth. Specimens also have an oval pectoral gland and raised, oval supra-axillary gland. Specimens may also have visible ventrolateral glands (Rowley et al. 2016).

Leptolalax pallidus can be distinguished from other members of the genus by its morphology, advertisement call, and molecular data. Leptolalax pallidus has a distinct ventral coloration that differentiates it from L. aereus, L. croceus, L. bourreti, L. eos, L. firthi, L. fuliginosus, L. heteropus, L. kecil, L. melanoleucus, L. minimus, L. nahangensis, L. nyx, L pelodytoides, L. platycephalus, L. pluvialis, L. solus, L. sungi, L. tuberosus, L. ventripunctatus, and L. zhangyangpingi. Iris coloration differs between the focal species and L. aereus, L. croceus, L. bourreti, L. botsfordi, L. eos, L. firthi, L. fuliginosus, L. kecil, L. melanoleucus, L. nahangensis, L. solus, L. sungi, L. ventripunctatus, and L. zhangyangpingi. Male body size differs from the focal species in L. bourreti, L. botsfordi, L. eos, L. fuliginosus, L. heteropus, L. kecil, L. melanoleucus, L. minimus, L. nahangensis, L. platycephalus, L. pluvialis, L. sungi, and L. zhangyangpingi. The presence of a black supratympanic line differentiates the focal species from L. bourreti, L. botsfordi, L. firthi, L. heteropus, L. kecil, L. melanoleucus, L. nahangensis, L. nyx, L pelodytoides, L. pluvialis, L. solus, L. tuberosus, and L. ventripunctatus. Skin texture differentiates the focal species from L. bourreti, L. fuliginosus, L. heteropus, L. melanoleucus, L. minimus, L. nahangensis, L. nyx, L. pluvialis, L. solus, L. tuberosus, L. ventripunctatus, and L. zhangyangpingi. The focal species can be differentiated from L. eos, and L. firthi because the focal species lacks lateral fringes on the toes (Rowley et al. 2016).

Specifically from the L.applebyi group, which L. pallidus is part of, an indistinct brown supratympanic line, tuberclated skin, and advertisement call differentiates L. pallidus from the rest of the group (L. applebyi, L. bidoupensis, L. melicus, L. pyrrhops, L. ardens, L. kalonensis, L. maculosus, and L. tadungensis). More specifically, the focal species has a larger body size than L. applebyi, L. bidoupensis, L. melicus, L. ardens, and L. maculosus but smaller than L. pyrrhops, and L. kalonensis. Various other morphologies are also different between the focal species and individual species in the group including tibia length, head width, pectoral gland size, tympanum diameter, iris color, distance between the eye and the tympanum, and eye diameter (Rowely et al. 2016).

In life, the frog has a brown back marked with dark interobital bars and pale brown spots on the anterior and posterior sides. In the armpits, there is a faint W-shaped mark. There is a darker brown line along the supertympanic ridge that encompasses most of the tympanum and ends at the arm insertion. The thighs, tibia, tarsus, lower arms, finger, and toes have transverse dark brown bars on the dorsal surfaces. The elbows and upper arms are paler brown. The sides from the groin to arm insertion have many small dark brown spots. The ventral surface is dark brown with white speckling on the throat, chest, and belly. The ventral surfaces of the limbs also have white speckles, but it is more sparse. The femoral, pectoral, and ventrolateral glands are white. The supra-axillary gland is copper. The upper half of the iris is copper and the lower half is gold with black reticulations. In preservation, the posterior region becomes slightly paler. The fingers and toes also become a somewhat paler brown color. The elbows are distinctly paler in preservative. The ventrum is a medium brown with faint white speckles. The macroglands become a creamy white color (Rowley et al. 2016).

There is a degree of variation on dark brown pattern on the dorsum and spread of the white spots on the ventral surface (Rowley et al. 2016).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Viet Nam

View distribution map in BerkeleyMapper.

Leptolalax pallidus has been found in Gia Rich mountain, Bidoup Nui Ba National Park, Vietnam in evergreen forests between 1644 – 1681 m on forest floors, leaf-litter, rocky crevices, and clay holes in dry stream banks (Rowley et al. 2016).

Life History, Abundance, Activity, and Special Behaviors
Male advertisement calls were recorded at ambient temperatures of 14.0 – 21.4^oC. Calls consisted of 4 – 7 notes and had an average duration of 673 ms. The calls started with short, low amplitude introductory notes that took up 22 – 26% of the call duration and had up to 63 pulses. The non-introductory notes consisted of a single pulse. The average dominant frequency of the call was 2.5 kHz. The call had a weak harmonic of ~7.3 kHz, an indistinct fundamental frequency, and sounded like a squelch followed by a clicking (Rowley et al. 2016).

Trends and Threats
The forest habitat where the species is found in is known to be disappearing, but no data on the frog is yet available (Rowley et al. 2016).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities

Comments
The species authority is: Rowley JJL, Tran DTA, Le DTT, Dau VQ, Peloso PLV, Nguyen TQ, Hoang HD, Nguyen TT, Ziegler T (2016). ''Five new, microendemic Asian Leaf-litter Frogs (Leptolalax) from the southern Annamite mountains, Vietnam.'' Zootaxa, 4085(1), 63-102.

Based on Baysian Inference and Maximum-likelihood analyses of 16S ribosomal RNA L. pallidus is a member of the L. applebyi group. More specifically, L. pallidus is sister to L. kalonensis, which was described at the same time as L. pallidus. The next most closely related species is L. bidoupensis (Rowley et al. 2016).

The species epithet, “pallidus” was chosen for the frog’s paler color in life and in preservative relative to other Leptolalax species known at the time (Rowley et al. 2016).

Leptolalax pallidus’ range may overlap with L. bidoupensis (Rowley et al. 2016).

References

Rowley JJL, Tran DTA, Le DTT, Dau VQ, Peloso PLV, Nguyen TQ, Hoang HD, Nguyen TT, Ziegler T (2016). ''Five new, microendemic Asian Leaf-litter Frogs (Leptolalax) from the southern Annamite mountains, Vietnam.'' Zootaxa, 4085(1), 63-102.

Species Account Citation: AmphibiaWeb 2017 Leptobrachella pallida <https://amphibiaweb.org/species/8461> University of California, Berkeley, CA, USA. Accessed Apr 20, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 20 Apr 2024.

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