Minervarya andamanensis (Stoliczka)

Gopika, C., Garg, Sonali, Sivaperuman, Chandrakasan, Gokulakrishnan, G. & Biju, S. D., 2023, Larval morphology and natural history in two Minervarya species from Andaman Islands, with comments on a new phytotelmonous larval morphotype for the genus, Zootaxa 5353 (6), pp. 567-581 : 569-572

Minervarya andamanensis (Stoliczka)

Breeding and early development ( Fig. 1 ). As a prolonged breeder, Minervarya andamanensis continues breeding activities for nearly three months. The most active breeding period is during the first half of the monsoon season, usually between the months from May to June. Males usually vocalise in a chorus from the edges of water bodies or shallow waters (rarely on the deeper side), from 17:00 hrs until 01:00 hrs. Males inflate a pair of externally visible subgular vocal sacs while emitting advertisement calls ( Fig. 1A ). Vocal sacs are yellowish to dark grey in colour. Female approaches a calling male and the male mounts the female in axillary amplexus ( Fig. 1B ). Oviposition sites vary from temporary water collection sites (such as roadside puddles and water-filled abandoned boats) to small permanent water bodies (such as ponds, fountain areas, and ditches). Spawning takes place mostly during the early morning hours, between 02:00–04:00 hrs. In the spawning sequence, the breeding pair spends more than two to three hours in amplexus before initiation of spawning. During this time, the amplectant pair usually remains in shallow waters or on ground close to the water bodies. The pair often moves towards the vegetated zone of the water bodies, where the female lays eggs on the water surface.

Female produces eggs in bouts, and after each bout of egg extrusion the male pushes the eggs close to his cloaca with noticeable arching of the body. The entire process of egg-laying can be divided into a series of bouts of egg release, followed by fertilisation. In each bout female releases between 8– 30 eggs, and while doing so the female raises her cloaca towards the water surface by submerging her head down into the water. The egg-laying process completes in 5–10 minutes ( Fig. 1C ). The egg clutch size varies from 80– 120 eggs, and the freshly laid eggs are half creamy-white and half light brown to black. Individual eggs with jelly cover measure 3.3 ± 0.5 mm in diameter ( Fig. 1D–F ). Embryonic development was not studied in detail; however, cleavage was observed to initiate within an hour of spawning ( Fig. 1G–I ), and further cell division was found to complete in three days ( Fig. 1J,K ). At this stage, the developing embryos sunk in water, where they underwent further larval development ( Fig. 1L ).

Larval morphology (Gosner Stage 35, n = 1; Fig. 2 ). In dorsal view, body is broader than tail (TMW 30% of BW), elliptical-shaped, and has maximum body width at the gill region. The body is depressed with body height 83% of body width. Body length constitutes 37% of total length. Snout shape in the lateral view is roughly rounded from plane of the eye to the base of upper labium. The narial opening is moderately sized, dorsolaterally oriented, and has a marginal rim. The nares are closer to snout than the eyes. The eyes are of moderate size and dorsolaterally positioned. Internarial distance is 50% of the interorbital distance. The spiracle opens sinistrally at the level of the hindlimbs and is located near the mid-point of the body (SS 69% of BL). The spiracular aperture is of moderate size and opens in the dorsoposterior direction. The inner wall of the spiracular aperture is fused with the body wall through a small ridge. The vent tube is tubular and opens dextrally at the base of the lower tail fin. The dorsal wall of vent tube is medially attached to the lower fin. Tail is of moderate size (TAL 63% of TL). Tail musculature is well developed (TMH 54% of MTH and 46% of BH, and TMW 30% of BW). Upper fin originates before the body-tail junction, and lower fin starts near the ventral terminus of body. The upper and lower fins gradually increase in height, reach maximum height at the mid-region of the tail, and taper into a tail tip. The tail muscle shows maximum height at the body-tail junction, gradually tapering and ending before the tail tip. Upper fin is higher than the lower fin (UFH 35% of MTH and LFH 12% of MTH). The tail tip is acutely pointed ( Fig. 2A–D ).

The oral disc is anteroventrally positioned, elliptical in shape horizontally, and relatively small in size (ODW 37% of BW). Lower labium is larger than the upper labium and lateral emarginations are present. The margin of upper labium is demarcated by a single irregular row of small, elongated marginal papillae laterally, with a wide dorsal gap in the middle. The lower labium has two irregular rows of small, elongated marginal papillae with a moderate-sized ventral gap. A few submarginal papillae are present inside the marginal papillae on the lower labium, near the lateral emarginations, and a few on the lateral side of upper labium. The labial tooth row formula is 2(2)/3. The tooth rows are uniserial. Labial teeth are well keratinised and have a curved spatulate apical tip with four to five marginal cusps. The jaw sheaths are moderately keratinised and nearly similar sized. The upper sheath is broadly arched, with the medial portion nearly straight, while the lateral tips end with a sigmoid curvature. The lower sheath is V-shaped. Sheaths possess short and broad-based serrations ( Fig. 2E,F ).

Colour in life. The overall colour of the tadpole is beige with a darker shade on the body. Dark melanocytes are distributed on the dorsal and lateral surfaces of the body, especially accumulating on the cheeks (posteroventral to the eyes), otic region, and dorsal half of the abdominal region. In the tail region, dark melanocytes are dusted on the tail muscle and more scarcely on both the fins. Dark melanocytes are faintly present on the lateral surfaces of the developing limb buds and the spiracle. The ventral surface of the body is pigmented only by golden iridocytes that partially cover the gut coil. The gills are visible through the cheeks and ventral surface of the body. The dorsal and lateral surfaces of the body are studded with golden iridocytes. Laterally, the golden pigmentation is mostly concentrated on the cheeks, abdominal region, and the lateral surfaces of the limb bud. A few golden iridocytes are speckled throughout the tail. Myosepta are evident in the tail musculature. The eyes are black in colour with golden iridocytes scattered in the sclera, which get denser towards the pupil forming a golden ring around it. The oral disc is unpigmented.

Measurements (in mm). TL 25.26, BL 9.23, SU 9.13, BH 4.99, BW 5.96, IOD 2.92, NE 1.69, SN 0.96, IND 1.47, SS 6.45, TAL 16.03, MTH 4.19, TMH 2.28, TMW 1.79, ODW 2.19, LFH 0.49, UFH 1.48. Additional morphometric measurements for different stages of tadpoles are provided in Table 1 .

Ontogenetic variation. The jaw sheaths remain well keratinised from Stage 25 to 42. The keratinised structures are well developed at Stage 25 even though A2 and P3 are more feebly keratinised than in the later stages. The LTRF remain unchanged until Stage 42, but the labial teeth in P2 and P3 are feebly keratinised in comparison to the previous stages. Occasionally, small tooth rows are seen on the lateral side of A2.

Figures

FIGURE 1. Breeding sequence and development in Minervarya andamanensis. A. Calling male with paired subgular vocal sacs; B. amplectant pair; C. close up of cloacal regions of the amplecting pair at the time of egg laying; D. freshly laid pigmented eggs; E. pigmented view of freshly laid eggs; F. close-up of a single freshly laid egg surrounded with jelly layer; G–I. cleavage of the egg after two hours (eight-celled stage); J. cleavage after five hours (sixteen-cell stage); K. tailbud stage after 40 hours; L. lateral view of a Gosner Stage 35 tadpole. Photographs: SDB and GG.

FIGURE 2. The tadpole of Minervarya andamanensis, Gosner Stage 35 (SDBDU 2021.4215). In life: A. lateral view; B. dorsal view; C. ventral view; D. frontal view. Oral disc: E. in preservation and F. illustration. Photographs: SDB.