Limnonectes isanensis McLeod, Kelly, and Barley, 2012

Ampai, Natee, Rujirawan, Attapol, Arkajag, Jirachai, Mcleod, David S. & Aowphol, Anchalee, 2015, Description of the tadpoles of two endemic frogs: the Phu Luang cascade frog Odorrana aureola (Anura: Ranidae) and the Isan big-headed frog Limnonectes isanensis (Anura: Dicroglossidae) from northeastern Thailand, Zootaxa 3981 (4), pp. 508-520 : 514-517

Limnonectes isanensis McLeod, Kelly, and Barley, 2012

Specimens examined. Five tadpoles of L. isanensis (ZMKU AM 0 1140 [n=3], ZMKU AM 0 1141 [n=1] and ZMKU AM 0 1142 [n=1]) were collected from Ron Ton Son Stream, Phu Luang Wildlife Sanctuary, Loei Province (17°17'53.2"N 101°31'22.1"E, 1,361 m ASL). Specimens were collected by Anchalee Aowphol, Attapol Rujirawan, Natee Ampai, Korkhwan Termprayoon, and Somphouthone Phimmachak on 28 July 2012 (2100 hr) and 11 December 2012 (2045 hr). A single tadpole specimen (ZMKU AM 01142; stage 38) was photographed in life and illustrated ( Figs. 6–7 ). A single adult specimen (ZMKU AM 01139; Fig. 5 A) was collected at Nam San Noi Stream, Phu Luang Wildlife Sanctuary, Loei Province (17°20'01.0" N 101°30'35.0"E, 915m ASL) by Anchalee Aowphol, Attapol Rujirawan, Natee Ampai and Somphouthone Phimmachak on 26 September 2012 (2030 hr).

Identification. Tadpole (ZMKU AM 01140) has an uncorrected pairwise divergence of 0.18 % from an adult specimen (ZMKU AM 01139). Morphology of the adult specimen of L. isanensis matched the original description ( McLeod et al. 2012).

Measurement of tadpole. Morphometric measurements (in mm) at Gosner (1960) developmental stage 38: BH = 5.9; BL = 13.4; BW = 7.9; IND = 2.8; IOD = 4.0; IOS = 2.6; MTH = 6.8; ODW = 2.4; SS = 7.7; TAL = 26.9; TL = 40.3; TMH = 3.1; TMW = 3.2; HUF = 2.2; HLF = 1.5.

Variation within the series. Mensural and ratio values for external morphology of the tadpole series (Gosner stages 30–38; n = 5) is provided in Table 1 . External morphology of the tadpoles remains generally consistent throughout the developmental stages in this series. In all specimens the sinistral spiracle and intestine coils were visible in lateral and ventral views. In early stages 30–35, the tail is weakly mottled whereas in later stages (e.g., Gosner 38), the tail is much more densely mottled.

Description of tadpole. Body moderate ( Fig. 7 A). From above, body oval, length twice width, wider anteriorly than posteriorly, snout rounded; in profile body depressed, sloping steeply from level of eyes, oral disc anteroventral. Nares are small, rim slightly elevated, anterodorsally positioned, closer to the snout than eye. Eyes dorsolaterally positioned at the end of the anterior quarter of body (closer to nares than spiracle), widely spaced relative to nares ( IND /IOD = 0.70), not visible from ventral view. Single, sinistral, tubular spiracle, opening below body axis near midpoint of body SS = 7.7 mm ( Fig. 7 A–B). Vent tube dextral, opens midway between muscle and edge of ventral fin; both of fins slightly convex ( Fig. 7 B). Tail musculature well developed, tail tapering gradually to pointed tip. Fin beginning at root of tail, margin of dorsal fin slightly higher than ventral fin and convex, ventral fin parallel to dorsal fin, TMH = 3.1 mm.

Color Pattern. Color in life (Stage 38, Fig. 7 ): body pale brown to yellowish with slightly darker brown pigment. Many small, thin, golden-yellow stripes on the sides of body and on dorsum of tail musculature. Dorsum and tail with many dark brown to black spots. Oral disc pale white. Venter of body nearly transparent, lightly flecked with gold; centro-sinistral intestine visible. Ventral surface of tail is semitransparent to white; caudal musculature faintly pale brown in dorsal view, with the upper and lower fins transparent. In preservative, coloration similar to specimen in life, pale yellowish stripes on ventrolateral body, dark brown pigmentation on tail remains distinctly visible.

Oral disc. Oral disc ( Fig. 6 B), anteroventral, 5–6 marginal papillae at corners of upper labium, papillae on upper labium larger than lower lip, upper and lower jaw sheathes medium, slight medial convexity, margin serrated, black. Separation between individual denticles narrow, LTRF: 2(1)/3(1); first row without gap, second row sub-equal left and right. The first lower labial tooth row with narrow median gap. Third lower labial tooth row nearly half the length of first and second rows.

Ecology. Tadpoles were collected from a shallow pool (12–15 cm deep) at the edge of a permanent stream (4 m wide, 60 cm deep) at 0 845 hr on 11 December 2012 ( Fig. 5 B). Ambient air temperature = 22.8°C, surface water temperature = 17.9°C, water pH = 6.14, and stream current was slow (0.1 m /s). Tadpoles were abundant at the study site during the study period. During the daytime, tadpoles were occasionally seen in the water column, but were predictably found buried in the gravel substrate or hiding beneath clumps of leaves at the bottom of the pools in the stream. When disturbed, tadpoles were observed to swim quickly to new hiding places. At nighttime, tadpoles were active in the water column. Egg masses containing 35–40 ova with transparent external jelly were found in clumps stuck to rocks in stream or to stream bank at the same location as the tadpoles during December (2012) and September (2013). Individual eggs encased in a jelly capsule measured 4–5 mm. Adult males of L. isanensis were found perched either on the ground amidst leaf litter, or on rocks on the bank of the stream at this site.

Comparisons. McLeod et al. (2012) described the PLWS endemic, L. isanensis , based on adult morphology, but provided no tadpole information. Our description of the tadpole of L. isanensis closely match the general characteristics of genus Limnonectes tadpoles described by Altig & McDiarmid (1999). McLeod (2008) provided morphometric data from a series of tadpoles and the description of the external morphology of a Gosner stage 40 tadpole of L. megastomias from Sa Kaeo Province, in eastern Thailand. Limnonectes megastomias is the sister taxon of L. isanensis and adults of both species are morphologically very similar ( McLeod et al. 2012). Despite this overall adult similarity, the tadpoles of L. megastomias and L. isanensis differ notably in several features. Measurement proportion of two species is shown in Table 2 . In overall size, the tadpole of L. isanensis seems to be smaller than L. megastomias , particularly during early stages of development (TL = 27.1–40.3 mm and 31.3–39.8 mm, respectively). Nevertheless, relative to total length, the body of L. isanensis appears to be larger than L. megastomias . When comparing tadpoles of the same developmental stage, Limnonectes isanensis was found to have a significantly greater body height (BH), the ratio of body height (BH) to body length (BL) and consequently in the ratio of body width (BW) to body length (BL) than L. megastomias (P <0.05). Oral disc structure and pattern of pigmentation on the body tail were also different in two species. Marginal papillae on the upper labium in L. isanensis are arranged in single row with about 5–7 papillae per side, two rows of papillae on the lower labium with about 20–22 papillae per side, a very narrow gap in the posterior marginal papillae, and the occurrence of two submarginal papillae ventrally. Tadpoles of L. megastomias have a single row of upper labial papillae, about 11–13 thick papillae of upper labium per side and about 28–30 papillae per side on lower labium arranged in two rows with narrow median interruption (but broader than in L. isanensis ). The caudal musculature and fins are more heavily pigmented in L. isanensis (dark brown to black on posterior half of tail) than in L. megastomiasis (faint brown spots scattered over length of tail). Additionally, tadpoles of L. megastomias have a median dark-brown horizontal bar through eye, which L. isanensis lacks.

Figures

FIGURE 5. (A) Adult male of the Isan big-headed frog, Limnonectes isanensis, (B) The habitat of L. isanensis at Phu Luang Wildlife sanctuary.

FIGURE 6. Limnonectes isanensis tadpole (ZMKU AM 01142; Gosner stage 38); (A) lateral view, (B) oral disc. Scale bar = 1 mm.

FIGURE 7. Limnonectes isanensis tadpole (ZMKU AM 01142; Gosner stage 38) in life; (A) Dorsal view, (B) ventral view, and (C) lateral view. Scale bar = 1 mm.