Heterixalus luteostriatus (Glaw & Vences, 2007)

Griep, Stine & Glos, Julian, 2020, Description of tadpoles of the frogs Heterixalus tricolor, H. carbonei and H luteostriatus (Anura: Hyperoliidae) from western Madagascar, Zootaxa 4767 (2), pp. 332-344 : 340-341

Heterixalus luteostriatus

The description of the external morphology is based on a specimen in stage 30, field number 2_Kirindy, from Kirindy Forest (TL 21.58 mm, BL 8.64 mm; Table 1-2 , Fig. 3 ).

External morphology. In the dorsal view, the body has an ovoid form with its widest point in the distal half to three-quarters of the body. The snout is broadly rounded. In profile, the body is depressed (BW 126% of BH), with its highest point in the distal half shortly behind mid-body. The snout is pointed. Moderately sized eyes (ED 13% of BL) are in a lateral position with a dorsolateral orientation. They are not visible in the ventral view. Nares are externally invisible. The spiracle is sinistral and visible in the dorsal view. It opens posterodorsally, at the broadest part of the body, slightly below the level of the proximal end of the tail myotomes axis. Its inner wall is free from the body. The vent tube is dextral, very short, and not attached to the ventral fin. The coiled gut is visible in an irregular shape. The tail reaches a length of about one and a half body lengths (TAL is 150% of BL). The tail muscle, which reaches the pointed tail tip, is narrow (TMW 36% of BW) and low both in the origin (TMH 46% of BH) and at mid-tail (TMHM 36% of THM). At its maximum height, which lies in the proximal quarter to half of the tail, the tail has a similar height as the body (MTH 98% of BH). More distal, at mid-tail, the tail height remains comparably high (THM 97% of MTH).

Dorsal and ventral fins have their pointed origin at the body tail junction. Both fins reach their maximum height, which is lower in the ventral fin than in the dorsal fin, in the proximal quarter to half of the tail. The height remains mostly constant until both fins start converging in the distal half of the tail to a pointed tail tip.

The oral disc is small and generalized without emargination (ODW 29% of BW). It has an anteroventral position and orientation. On the lower labium, there is a single row of very few marginal papillae. Ventrally and laterally, there are some submarginal papillae. The papillae are rounded and form a moderately sized dorsal gap (DG 60% of ODW). The LTRF is 1/3(1), P3 is much shorter than P1 and P2. The upper tooth row is about half as wide as the oral disc (A1 53% of ODW). Serrated labial teeth have two to three cusps. The wide jaws sheaths (JL 71% of ODW) have edges with pointed serrations. The upper jaw sheath has a broad, round form while the lower one is V-shaped. Both jaws sheaths are half keratinized.

Coloration in preservative. Dorsally, the body of the tadpole shows uniform pigmentation. Laterally, the pigmentation pattern is fading. Pigmentation is particularly sparse in the area between the pigmented spiracle and the tail. There are parts of light brown pigmentation on the transparent abdomen, the coiled gut is visible. The limb buds are without pigmentation. The eyes are black. A pattern of uniformly pigmented patches covers the tail. Scattered spots of pigmentation are visible in the papillae of the oral disc. The teeth and the keratinized parts of the jaws sheaths are blackish-brown.

Variation. The external morphology and general appearance were very similar between specimens. The ratios taken on five tadpoles in stages 25 to 34 vary in the following proportions: BH 116-127% of BW; ED 12-13% of BL; TAL 150-168% of BL; TMW 21-36% of BW; TMH 29-49% of BH; TMHM 31-36% of THM; THM 83-97% of MTH; MTH 82-98% of BH; DF 103-131% of TMHM; VF 67-95% of TMHM; DF 122-164% of VF; ODW 25-29% of BW; DG 44-68% of ODW; A1 50-69% of ODW; JL 54-71% of ODW.

Morphometric differences between species

When performing an NMDS, all five individuals within a species formed clear clusters that separated mainly along axis 1 ( Fig. 4 ). The stress value (0.16) of the final two-dimensional solution indicated a reasonable preservation of ordering relationships of the multidimensional dissimilarities. Morphometry along this axis differed significantly between species (PerManova: TSS = 0.81, F = 6.69, p <0.001, n = 15). Pairwise comparisons revealed significant differences between all species combinations (p <0.05 for all combinations).

Figures

FIGURE 3. Tadpole of Heterixalus luteostriatus in (A) the lateral and (B) the dorsal view, its oral disc (C) under the scanning electron microscope, (D) labial teeth from P1.

FIGURE 4. NMDS plot of Heterixalus tricolor (open circles), H. carbonei (+), and H. luteostriatus (filled circles) with five individual tadpoles per species based on 18 size corrected, morphometric characters (stress = 0.16).