Micryletta hekouensis, Liu, Hou, Mo & Rao, 2021

Nguyen, Tan Van, Liu, Shuo, Tran, Vy The, Tran, Thinh Gia, Trofimets, Alexei V., Dau, Vinh Quang & Poyarkov, Nikolay A., 2024, Range extension and expanded description of Micryletta hekouensis Liu, Hou, Mo & Rao, 2021 (Amphibia, Anura, Microhylidae), with comments on Micryletta of Northern Vietnam, Herpetozoa 37, pp. 111-121 : 111

Micryletta hekouensis

, Fig. 2

Micryletta cf. inornata - Poyarkov et al. (2018: 1-27, in part); Miller et al. (2021: 248, in part).

Micryletta cf. steinegeri - Poyarkov et al. (2021a: 42-43, in part).

Micryletta hekouensis - Liu, Hou, Mo & Rao (2021: 133).

Micryletta hekouensis - Sankar et al. (2022: 462).

Holotype.

KIZ 20210510, adult male collected by Shuo Liu on 15 May 2021. Type locality: Nanxi Village, Nanxi Town, Hekou County, Honghe Prefecture, Yunnan Province, China (22°38'17"N, 103°59'8"E; elevation 350 m a.s.l.).

Suggested name in Vietnamese.

Nhái bầu Hà khẩu.

Specimens examined

(n = 12). Two adult males DTU 310, 316 and four adult females DTU 309, 311-312, 317 from Cuc Phuong NP, Ninh Binh Province, Vietnam (ca. 20.2594°N, 105.6928°E; elevation of 160-215 m a.s.l) collected by Tan Van Nguyen on 3 June 2018 . Three adult males ZMMU NAP-2176, ZMMU NAP-3580, ZMMU NAP-5572 and three adult females ZMMU NAP-3352, ZMMU NAP-3574, ZMMU NAP-5574 from Cat Ba NP, Hai Phong Province, Vietnam (ca. 20.8123°N, 106.9988°E; elevation of 90 m a.s.l.) collected by Nikolay A. Poyarkov in October 2013 .

Variation based on examined specimens from Vietnam

(n = 12). According to the original description of Liu et al. (2021a) the species M. hekouensis is a small-sized species of Micryletta with SVL 20.5 mm in adult male (Holotype, KIZ 20210510) and SVL 20.8 mm in adult female (Paratype, KIZ 20210511). However, the specimens from Vietnam exhibit generally larger body sizes: SVL 20.0-24.1 mm in males (n = 5), 25.4-29.5 mm in females (n = 7). Therefore, we propose that the paratype specimen should be considered a subadut female, and that M. hekouensis in fact represents a medium-sized species within its genus. Moreover, the TbL/SVL ratio in female specimens from Vietnam (0.43-0.55) was also slightly larger than in the paratype female from China (0.40). Furthermore, Liu et al. (2021a) reported this species to have a small rounded and distinct tympanum; however, the specimens from Vietnam had the tympanum hidden. It is not clear if the observed morphological differences between the type series of M. hekouensis from China and the series from Vietnam represent the actual intraspecific variation, or might result from the different state of specimen preservation, the reproductive condition of the specimens, or the observer effect. However, though we acknowledge the limitations of mtDNA markers for species delimitation in amphibians (e.g., Velo-Antón et al. 2023), the overall similarity of the Chinese and Vietnamese specimens of M. hekouensis in external morphological traits and coloration strongly suggest that they belong to the same species.

Additionally, the Vietnamese specimens examined were characterized by: habitus relatively slender; head small and triangular, width approximately equal to length (HW/HL 0.93-1.11 in males, 0.97-1.22 in females); snout abruptly rounded in dorsal view and slightly acuminate in profile, projecting beyond margin of lower jaw; eyes relatively small, slightly protuberant, pupil oval, transverse, eye diameter slightly equal to snout length (ED/SL 0.75-1.20 in males, 0.83-1.18 in females). Top of the head flat, canthus rostralis rounded and distinct; loreal region weakly concave; nostril round, closer to tip of snout than to eye; interorbital distance greater than internarial distance (IOD/IN 1.26-2.16 in males, 1.20-1.71 in females) and upper eyelid width (IOD/UEW 1.45-1.91 in males, 1.30-1.89 in females). Tympanum and supratympanic fold indistinct. Choanae rounded; vomerine teeth absent; opening of vocal sac long cleft; tongue oval, with no notch at posterior tip.

Forelimbs: Forearm length ca. three times shorter than hand length (FLL/HAL 0.43-0.62 in males, 0.40-0.53 in females). Fingers slender with no webbing, rounded in cross-section, no lateral fringes; relative finger lengths: I<II<IV<III; tips of fingers round and not dilated; subarticular tubercles on fingers distinct, rounded and prominent, formula: 1, 1, 2, 2; supernumerary tubercles on palm present and developed; three metacarpal tubercles, inner one rounded and smallest, median one rounded and almost directly in front of oval outer one; two rounded and one elongated prominent supernumerary palmar tubercles on the base of fingers II-IV, respectively; nuptial pad absent.

Hindlimbs: Tibia slightly longer than thigh (FeL/TbL 0.80-0.97 in males, 0.82-1.02), approximately three times longer than wide (TbL/TbW 3.27-5.50 in males, 3.08-5.19 in females); tibiotarsal articulation of adpressed limb reaching eye; foot longer than tibia (TbL/FoL 0.60-0.67 in males, 0.59-0.68 in females). Relative toe lengths: I<II<V<III<IV; tarsal fold absent; tips of toes round and not dilated, slightly wider than those of fingers; webbing between toes absent; subarticular tubercles on toes oval and prominent, formula: 1, 1, 2, 3, 2; dermal ridges present under 2nd to 4th toes but indistinct; inner metatarsal tubercle rounded, prominent, and small; outer metatarsal tubercle absent.

Dorsal skin scattered with small tubercles on dorsum of body, flanks, and hindlimbs, dorsal skin of forelimbs smooth; subtle longitudinal median ridge present on dorsum; dorsolateral fold absent; lateral sides of head smooth; ventral skin of body and limbs smooth.

Colouration in life.

Coloration varies greatly, dorsum of body purple brown, blueish grey, or dark brown with two indistinct parallel longitudinal grey stripes on back. Dorsum of forelimbs light yellow, dorsum of hindlimbs the same color as dorsum of body, no bands on dorsum of limbs. Upper lip white. Ventral side of head, body, and limbs greyish brown, purple grey or pinkish brown. Chin region brownish black, males usually have a darker one than females, white marbling patterns on chest and belly, some white spots on chin region and ventral side of limbs. Iris bicolored, with upper third bronze and lower two-thirds brownish black.

Revised diagnosis.

Medium-sized within genus Micryletta (SVL 20.0-24.1 mm in males, 25.4-29.5 mm in females); areas above canthus rostralis, upper eyelids, areas posterior to eyelids, and dorsum of upper arms golden, other parts of dorsum almost solid black or yellowish grey with brownish black stripes; lateral sides of the head and body black or yellowish grey, a white stripe from lower front of eye along upper lip back to anterior forelimb insertion; ventral side of body and limbs pink brown, chin region in adult males brownish black, small and irregular white marbling patterns on chest and lateral belly; tympanum indistinct; supratympanic fold indistinct; outer metatarsal tubercle absent; webbing between toes absent; tibiotarsal articulation adpressed limb reaching level of eye (data from Liu et al. (2021) and this study).

Comparisons.

We summarize the main characters separating Micryletta hekouensis from the other twelve species of the genus Micryletta in Suppl. material 1. In Vietnam, previously this species was often recorded under the names M. steinegeri or M. inornata , therefore we focused on comparing the morphological characteristics of Micryletta hekouensis with these two species. Micryletta hekouensis differs from M. steinegeri by having:venter without dark patterns (vs. with greyish white and brown spots); webbing between toes absent (vs. rudimentary webbing); tibiotarsal articulation adpressed limb reaching level of eye (vs. reaching to tympanum). Micryletta hekouensis differs from M. inornata sensu stricto by having: lager body size in females (SVL 25.4-29.5 mm vs. 19.5 mm); ventral side of body and limbs pinkish brown or pinkish grey with small and irregular white marbling patterns on chest and lateral belly (vs. reddish grey without mottling, nearly immaculate, or chin, chest, and lateral belly with a few dark marbling patterns).

Distribution.

Micryletta hekouensis was previously known only from Nanxi Town, Hekou County, Honghe Prefecture, Yunnan Province, China (Liu et al. 2021). We here add further records of this species in Vietnam (Ninh Binh and Hai Phong provinces). The new location in Cat Ba NP is situated ca. 335 airline kilometers southeast of the type locality. Given the geographic proximity and distribution patterns of limestone-associated herpetofauna in Vietnam (see Poyarkov et al. 2021a, 2023), M. hekouensis likely occurs in several limestone karst massifs of Northern Vietnam; in particular, records from Quang Ninh, Lang Son and Bac Giang provinces of Northeastern Vietnam, as well as from Hoa Binh, Ha Nam, and Thanh Hoa provinces of Northwestern Vietnam are anticipated.

Natural history notes.

Prior to this study, biological data of Micryletta hekouensis were very limited; it was only reported from an altitude of 350 m a.s.l. (Liu et al. 2021). The species appears to be closely associated with karstic habitats ( Poyarkov et al. 2018; Liu et al. 2021). In Cuc Phuong NP, the frogs were observed from 16:00 to 20:00 h under the dead leaves on the ground. Other species of microhylids recorded syntopically with Micryletta hekouensis in Cuc Phuong NP included Kalophrynus interlineatus (Blyth, 1855), Glyphoglossus cf. yunnanensis (Boulenger, 1919), Kaloula pulchra Gray, 1831, Microhyla berdmorei (Blyth, 1856), M. butleri Boulenger, 1900, M. cf. heymonsi Vogt, 1911, M. mukhlesuri Hasan, Islam, Kuramoto, Kurabayashi & Sumida, 2014, M. pulchra (Hallowell, 1861), Micryletta nigromaculata Poyakov, Nguyen, Duong, Gorin & Yang, 2017, and Vietnamophryne cf. orlovi Poyarkov, Suwannapoom, Pawangkhanant, Aksornneam, Duong, Korost & Che, 2018. In Cat Ba NP, the frogs were observed from 16:00 to 20:00 h hiding between small pieces of limestone rocks. Other species of microhylids recorded syntopically with Micryletta hekouensis in Cat Ba NP included Kaloula pulchra , Microhyla butleri , M. fissipes Boulenger 1884, M. cf. heymonsi , M. pulchra , Micryletta nigromaculata . We also recorded gravid females of M. hekouensis in June in Cuc Phuong, but other reproduction biology data, such as advertisement call, tadpole morphology, as well as diet of the species remains unknown. It is remarkable that in both localities of Micryletta hekouensis in Vietnam, this species was recorded in syntopy with M. nigromaculata , another species of the genus Micryletta strongly associated with limestone karst formations of northern Vietnam.

Figures

Figure 2. The Micryletta hekouensis alive: from Cuc Phuong NP., Ninh Binh, Vietnam. A, B. DTU 316, adult male; C. DTU 311, adult male; D, E. DTU 317, adult female); from Cat Ba NP, Hai Phong, Vietnam; F, G. ZMMU NAP- 3580, adult female); from Hekou, Yunnan, China; H. KIZ 20210510, holotype, adult male; I. KIZ 20210511, paratype, subadult female). Photos by: TV. Nguyen (A-E), NA. Poyarkov (F, G), and L. Shuo (H-K).