Description
Nasikabatrachus sahyadrensis is a relatively large burrowing frog with a distinct, bloated appearance. Snout-vent length ranges from 52.8 mm to 89.9 mm (Radhakrishnan et al. 2007). Males are about one third the size of females (Zachariah et al. 2012). The head is small and relatively short in comparison with the rest of the body. The snout ends in a white, knob-like protrusion. The mouth is ventral, with a narrow gape. The upper jaw is rigid while the lower jaw is flexible and flaplike, enabling a grooved aperture to be formed through which the tongue can be protruded. The tongue is basally attached, small and fluted, with a rounded tip. Maxillary teeth are absent. Eyes are small, with a prominent upper eyelid and a lower eyelid consisting of a small skinfold. Males have a single subgular vocal sac (Zachariah et al. 2012). The tympanum is lacking. Both the forelimbs and hindlimbs are short. Palms are hard with rounded fingertips (but no discs) and barely webbed fingers. Feet have rounded toe tips (no discs) and are 3/4 webbed. Each hindfoot possesses a large, white, shovel-like inner metatarsal tubercle, used for digging. Irises are black, with a rounded, horizontal pupil. This species has smooth, black skin dorsally which fades into gray ventrally (Biju and Bossuyt 2003; Radhakrishnan et al. 2007).

The skeletal structure of N. sahyadrensis is characteristic of a burrowing frog, with a strongly ossified skull and well-calcified bones. Due to the species' unique appearance, as well as specific osteological differences, Biju and Bossuyt (2003) placed N. sahyadrensis in a new anuran family, named Nasikabatrachidae. Although some traits are shared with the sister group, Sooglossidae, the authors concluded the lack of toe discs and much larger size, as well as other characters, significantly separate N. sahyadrensis from Sooglossidae (Biju and Bossuyt 2003).

N. sahyadrensis tadpoles have a wide, flattened, wedge shaped snout. The nostrils are located on top of the head, closer to the eyes than the snout tip. Eyes are small and located dorsolaterally. The oral disc is suctorial and ventrally located. Body is wide and flattened. The tail is low relative to the body, dorsal and ventral fins are about the same height. The tail is about two thirds of the total length. The dorsum is dark brown, while the ventral surface is a silvery cream color. The eyes are black. The tail is light brown, with dark brown patches throughout (Raj et al. 2012).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: India

View distribution map in BerkeleyMapper.

Nasikabatrachus sahyadrensis appears to be endemic to the Western Ghat Mountains of southern India. This species has been found in disturbed secondary forest located close to a cardamom plantation at Kattappana in the Idukki district of Kerala, at an altitude of around 900 m (Biju and Bossuyt 2003). It has also been found at Sankaran Kudi in the Anamalais, Tamil Nadu; Indira Gandhi Wildlife Sanctuary, Pollachi, Tamil Nadu; Murikkassery (near Kothamangalam), Ernakulam district; and the Manimala River at Erumely, Kottayam district (Dutta et al. 2004). Most recently it has been found 3 feet underground, while excavating pits in a cleared area of disturbed forest habitat, on a rubber plantation (Karuvarakundu, Malappuram district, Kerala), at 500 m asl (Radhakrishnan et al. 2007). Two specimens were found at this locality, in subsequent years, during monsoon season (July and August; Radhakrishnan et al. 2007). The habitat consisted of cocoa and coffee plants on the hilltops, and rubber plants on the slopes, with forest loam on the soil surface and red soil underneath, and a barely running stream (Radhakrishnan et al. 2007).

As of 2012, the species ranges from Camel's Hump Hill Range in the north to the northern reaches of the Agasthyamalai Hill Range in the south, in the Western Ghats of India. It inhabits an elevational range of 60-1100 meters above sea level (Zachariah et al. 2012).

Life History, Abundance, Activity, and Special Behaviors
Male N. sahyadrensis call from inside shallow burrows nearby streams. The fundamental frequency of the call is 1200 Hz, with 5-6 pulses per note. Choruses typically occur on rainy evenings (lasting until dawn) from late April to mid-May (Zachariah et al. 2012).

N. sahyadrensis is an explosive breeder, laying large numbers of eggs during the earliest rains of the pre-monsoon season. Additionally, the tadpoles are lentic, inhabiting fast flowing seasonal streams. The unique timing of reproduction and tadpole habitat significantly reduces competition (from other anuran larvae) and predation. The eggs are laid so early that there has not been time for predators to significantly establish themselves in the stream, and by the time other organisms have settled in, the tadpoles have moved to fast flowing waters over sheer rock, where there is little threat from predators (Zachariah et al. 2012).

Eggs are laid in rocky crevices at the edges of second-order streambeds. During amplexus, the male grasps the female's spine (as there are no adhesive glands present and the male is very small relative to the female). The female then carries the male to suitable oviposition sites, where he pushes the eggs out of the female with his hindlimbs and fertilizes them. The eggs are deposited in arrays or clumps. One mating pair deposited about 3600 eggs in one night (Zachariah et al. 2012).

N. sahyadrensis tadpoles are known to feed out of the water at night, using their strengthened abdominal muscles to move onto surfaces with extremely shallow water flow (Zachariah et al. 2012). Tadpoles take about 100 days from hatching to metamorphose (Raj et al. 2012).

N. sahyadrensis is fossorial and comes to the surface only for a few weeks a year to breed (Biju 2004). Sightings are more likely at the beginning of monsoon season, in July (Radhakrishnan et al. 2007). A captured specimen was reported to be able to dig itself into loose soil within 3-5 minutes. When placed on a pebbled gravel surface within an open, dry streambed, the frog tried to escape with stretching movements (not hopping). The pointed snout is touch-sensitive. In captivity, the frog used its hindlimbs for burrowing, with Radhakrishnan et al. (2007) providing a detailed description of the burrowing process. During five months of captivity, the frog did not emerge from the soil, even at night, although it moved about underneath the soil. Given the hard-knobbed snout and small ventral mouth, this species is likely to be a completely underground feeder specializing in termites (Dutta et al. 2004; Radhakrishnan et al. 2007).

Other frogs with similar lifestyles and morphology include those of the genus Rhinophrynus and Hemisus (Radhakrishnan et al. 2007).

Trends and Threats
This amphibian is found in the Western Ghats region of India, a biodiversity hotspot. Human encroachment, especially from crop farming, has reduced the forested area by greater than 90% (Myers et al. 2000). In addition, dam projects in the Western Ghats threaten large portions of this frog's habitat (Dutta et al. 2004). It has been found in disturbed forest but cannot tolerate completely cleared areas (Biju 2004). Around one third of the range of N. sahyadrensis is contained within protected areas in Kerala (Zachariah et al. 2012).

Relation to Humans
This frog was known to local people before two separate teams of herpetologists reported its discovery (Aggarwal 2004). Plantation workers turn this frog up when excavating trenches during the monsoon period from July to October (Radhakrishnan et al. 2007). Local people eat gravid N. sahyadrensis, believing that they have medicinal properties (Zachariah et al. 2012).

Thomas and Biju (Salamandra 2015) extensively documented tadpole consumption in Nasikabatrachus sahyadrensis. At a single study site in the Western Ghats of India, thousands of tadpoles were harvested per year, as well as adults. While potentially sustainable, the combination of heavy exploitation with annual variation in monsoon rains likely have a long-term negative impact on this threatened and biologically unique species.

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Urbanization
Disturbance or death from vehicular traffic
Drainage of habitat
Dams changing river flow and/or covering habitat
Intentional mortality (over-harvesting, pet trade or collecting)
Climate change, increased UVB or increased sensitivity to it, etc.

Comments
The species authorities for N. sahyadrensis are S.D. Biju and F. Bossuyt.

N. sahyadrensis tadpoles were first described in Annandale (1918), without specimens of adults. It was tentatively assigned to the family Cystignathidae (Raj et al. 2012).

In Sanskrit, nasika means "nose" and batrachus means "frog," while Sahyadri refers to the location where this species is found (the Western Ghats, also known as the Sahyadri Mountains, a low-lying mountain range along the west coast of the Indian subcontinent).

As pointed out by Hedges (2003), most of the anuran families were named in the mid-nineteenth century; the last time the discovery of a new species led to the description of a new family was in 1926 (Frost 2003). Based on a phylogenetic analysis of mitochondrial genes, Biju and Bossuyt (2003) suggest that this species, endemic to India, is a sister taxon to the Sooglossidae, a family of frogs endemic to the Seychelles Islands. This has lent support to the idea of a possible land bridge between Africa and India, enabling faunal dispersal. The species Nasikabatrachus sahyadrensis is estimated to have originated in the Jurassic, 130-180 million years ago (Biju and Bossuyt 2003; Dutta et al. 2004) which is 50 to 100 million years earlier than any other known frog species in India (Aggarwal 2004), and predating the breakup of the ancient continent Gondwana (Radhakrishnan et al. 2007; Dutta et al. 2004).

References

Aggarwal, R. K. (2004). ''Ancient frog could spearhead conservation efforts.'' Nature, 428, 467.

Biju, S. D. and Bossuyt, F. (2003). ''New frog family from India reveals an ancient biogeographical link with the Seychelles.'' Nature, 425, 711-714.

Dutta, S. K., Vasudevan, K., Chaitra, M. S., Shanker, K. and Aggarwal, R. K. (2004). ''Jurassic frogs and the evolution of amphibian endemism in the Western Ghats.'' Current Science, 86, 211-216.

Frost, D. R. (2003). ''Amphibian Species of the World: An Online Reference.'' Electronic database available at http://research.amnh.org/herpetology/amphibia/index.html. American Museum of Natural History, New York, USA.

Hedges, S. B. (2003). ''The coelacanth of frogs.'' Nature, 425, 669-670.

Myers, N., Mittermeier, R. A., Mittermeier, C. G., Da Fonseca, G. A. B. and Kent, J. (2000). ''Biodiversity hotspots for conservation priorities.'' Nature, 403, 853-858.

Radhakrishnan, C., Gopi, K.C., and Palot, M.J. (2007). ''Extension of range of distribution of Nasikabatrachus sahyadrensis Biju & Bossuyt (Amphibia: Anura: Nasikabatrachidae) along Western Ghats, with some insights into its bionomics.'' Current Science, 92(2), 213.

Raj, P., Vasudevan, K., Vasudevan, D., Sharma, R., Singh, S., Aggarwal, R.K., and Dutta, S.K. (2012). ''Larval morphology and ontogeny of Nasikabatrachus sahyadrensis Biju & Bossuyt, 2003 (Anura, Nasikabatrachidae) from Western Ghats, India.'' Zootaxa, 3510, 65-76.

Thomas A and Biju SD (2015). "Tadpole consumption is a direct threat to the endangered purple frog, Nasikabatrachus sahyadrensis." Salamandra, 51(3), 252-258. [link]

Zachariah, A., Abraham, R.K., Das, S., Jayan, K.C., and Altig, R. (2012). ''A detailed account of the reproductive strategy and developmental stages of Nasikabatrachus sahyadrensis (Anura: Nasikabatrachidae), the only extant member of an archaic frog lineage.'' Zootaxa, 3510, 53-64.

Species Account Citation: AmphibiaWeb 2021 Nasikabatrachus sahyadrensis: Purple Frog <https://amphibiaweb.org/species/6197> University of California, Berkeley, CA, USA. Accessed Dec 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Dec 2024.

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