Species Description: Biju & Bossuyt 2005 Current Science 88
Raorchestes nerostagona is a frog distinct to the rainforest canopy of the Western Ghats, India. It is small (34.0 mm SVL for males), and its head is broader than long. Pupils are oval and horizontal, and the snout is rounded. The tympanum is distinct and rounded. A supratympanic fold is present, running from the posterior of the eye to the base of the forelimb. On the snout, the skin is shagreened to granular, and glandular with short spinular projections on the side of the head, between the eyes, on the upper eyelids, and on the dorsum and flanks. The forelimbs and hindlimbs are shagreened dorsally with a few scattered granules. The throat, chest, belly and the posterior ventral part of thighs are glandular. Forelimbs are shorter than hands, and there is a dermal fringe along the outside of the forelimbs. Fingers have lateral dermal fringe and are moderately webbed. Subarticular tubercles are single, rounded and distinct. Supernumerary tubercles are prominent on fingers II and III and the palm. Relative finger length is as follows: III>IV>II>I. The tips of the fingers are expanded into oval discs with circummarginal grooves. Hindlimbs are moderately long, and the tips of toes are expanded into oval discs with circummarginal grooves. The toes show extensive webbing, and the relative toe length is IV>V>III>II>I. Similar to the forelimbs, the hindlimbs also have a distinct dermal fringe along the outside, ending with a spinular projection on the heel. Subarticular tubercles are rounded, and simple where present. The inner metatarsal tubercle is distinct and oval, and supernumerary tubercles are present on all fingers and toes. Nuptial pads are not present on the males. Vocal sacs are evident, however, and are median and subgular, with paired openings at the base of the throat (Biju and Bossuyt 2005).
This frog can be distinguished from all others in its genus by the combination of webbed fingers, toes with nearly full webbing, a dermal fringe along the outer side of the forelimbs and hindlimbs, and a pointed papilla on the tongue (Biju and Bossuyt 2005).
On the dorsum and the dorsal side of limbs, the frog is light brown with dark green and reddish-brown patches of varying size. Laterally, it is bluish-black and vermiculated with brown blotches. The loreal and tympanic regions are light brown with irregular light green patches, and the hands and feet are grey. The posterior edges of the femur and tibia are chocolate brown. Ventrally, the coloration is off-white with different amounts of brown, light gray, and light yellow spots in a vermiculated pattern. The lips of the frog are white with dark bands. The iris is reddish-gray with a brown ring. This species is capable of metachrosis as well, and is thus both highly variable in color and cryptic. It may, for example, resemble lichen-covered tree bark on which it rests (Biju and Bossuyt 2005).
Distribution and Habitat
This frog is associated with the regions of Sultanbathery, Kalpatta, and Mananthavady at an altitude of around 1,000 m asl, in the Wayanad District of Kerala State, in the Western Ghats of India. It lives almost exclusively in the highest canopy layer (at around 10-20 m above the ground) of tropical evergreen forests (IUCN 2006). The holotype was collected on a tree near the forest fringe, and the paratype was collected from a height of about 20 m in the forest canopy (Biju and Bossuyt 2005).
Life History, Abundance, Activity, and Special Behaviors
Raorchestes nerostagona is an arboreal species which dwells in the high canopy, at around 10-20 m above ground. Males vocalize frequently during the monsoon season. The unique calls resemble the sound of a drop falling into water. Calls occur at intervals of 3-4 seconds (Biju and Bossuyt (2005).
Female R. nerostagona deposit clutches of about 40 direct-developing eggs high in the rainforest canopy, in contrast to other species of the genus Raorchestes. A clutch of R. nerostagona eggs was found in a tree hole about 10 cm deep, at a height of 10 m. These eggs were white (non-pigmented) and protected by a dense layer of jelly, with each egg measuring 4.5 +/- 0.3 mm in diameter (Biju and Bossuyt 2005).
Trends and Threats
This species appears to be "nearly ubiquitous" in its limited range, based on hearing its calls during the monsoon season (Biju and Bossuyt 2005), but continues to face habitat loss due to habitat-replacement for cultivated lands, Eucalyptus, coffee and tea plantations, and hydroelectric reservoirs. A part of the species' range falls inside the Wayanad Sanctuary, but a need for heightened conservation is still present (IUCN 2006).
Possible reasons for amphibian decline
General habitat alteration and loss
This species was first described by S.D. Biju and Franky Bossuyt (2005). The name nerostagona is derived from a combination of two Greek words: nero, water and stagona, drop, referring to the mating calls that resemble drops falling into water.
Biju, S.D., and Bossuyt, F. (2005). ''A new species of frog (Ranidae, Rhacophorinae, Philautus) from the rainforest canopy in the Western Ghats, India.'' Current Science, 88, 175-178.
IUCN, Conservation International, and NatureServe. (2006). Global Amphibian Assessment: Philautus nerostagona. www.globalamphibians.org. Accessed on 04 May 2006.
Written by Alamelu Natesan (amluuu AT gmail.com), UC Berkeley
First submitted 2008-05-07
Edited by Kellie Whittaker (2010-09-28)
Species Account Citation: AmphibiaWeb 2010 Raorchestes nerostagona <http://amphibiaweb.org/species/6526> University of California, Berkeley, CA, USA. Accessed May 23, 2017.
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Citation: AmphibiaWeb. 2017. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 23 May 2017.
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