A frog with a stout and compressed body. Males are 32-48 mm (SVL) and females are 37-48 mm (SVL) (Kunte 2004; Bhaduri and Kriplani 1955). The head is broad, with a snout that is short and rounded. Eyes are bulging, directed forward and upward, and have narrow upper eyelids. Pupils are vertical. There is an oblique fold underneath the eye, and the upper eyelid has distinct tubercles. The tympanum is hidden beneath the skin. A relatively large, free-moving tongue is deeply notched behind. Vomerine teeth patches are present in two slightly oblique series, each with 6-8 teeth in a single row, separated by a narrow space, and set back from the choanae. The forelimb is short and robust with moderately long, semi-flattened fingers (3>4>2>1). Fingertips and toe tips are dilated into large discs with a horizontal circummarginal groove separating the upper from the lower surface; finger discs are mostly the same size except for the fourth one which appears slightly smaller. The palm has one or two tubercles. The hindlimb is similarly stout and somewhat long, with toes that are moderately flattened and completely webbed except for the fourth one (4>5=3>2>1). Subarticular tubercles are moderately developed, and a small inner metatarsal tubercle is present but no outer metatarsal tubercle. There is a deep fold of skin on the outer side of the fifth toe (Bhaduri and Kripalani 1955). Males have larger toe-discs than females, which may help in holding onto leaves during lengthy vocalization periods (Kunte 2004). Males lack vocal sacs (Bhaduri and Kripalani 1955) and they also lack the nuptial pads that are common to many male anurans (Kunte 2004).
Nyctibatrachus humayuni coloration in preserved specimens ranges from grayish to brownish black dorsally. If present, dorsal markings are irregular and darker. The venter is slightly gray, with ventral patterning usually consisting of dark stain-like blotches on the chin and throat. Limbs may have dark crossbars or spots (Bhaduri and Kripalani 1955). In life, adult males have colorful femoral glands which may be pale orange to bright orange or pink (Kunte 2004).
The tadpole is of moderate size (47 mm) at a stage where the legs are half developed. Its head and body are narrowly oval, and moderately flattened with the ventral surface being slightly convex. The tail is about one and a half times longer than the head and body, and it gradually narrows to a blunt point. The eyes are dorsolateral, pointing forwards and upwards, and the nostrils are widely spaced and nearer to the tip of the snout. The spiracle is lateral, sinistral, pointing upwards and backwards, and located about halfway been the tail and the tip of the snout. The vent is dextral. The mouth has a small oral disc which is surrounded by the anterior and posterior lips. The anterior lip is distinct, fringed with 3-4 rows of short papillae just above the upper beak, and can be closed down over the mouth. The posterior lip consists of 3 lobes, the upper part of which can be folded backwards. The upper beak is entirely black, and is relatively broader than the lower one, which is more stout, V-shaped, and consists of a whitish basal part. Both beaks are finely serrated. The tadpole itself is dark brown on its dorsal side and whitish on its ventral side, with irregular dark markings (Bhaduri and Kriplani 1955).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: India
This species is endemic to the Western Ghats mountains of the state of Maharashtra in southwestern India. Records from this state are primarily from Konya Valley, Bhimashankar, and Amboli.Nyctibatrachus humayuni is also prevalent in the states of Goa and Karnataka in southern India, mainly between Castle Rock and Dudhasagar. It has an altitudinal range of 200 to 1,200 m above sea level (Stuart et al. 2008). This species lives under stones and in crevices, in small, often steep and rocky hill-streams which have significant overhanging vegetation and run through thick evergreen and semi-evergreen forests (Bhaduri and Kripalani 1955; Kunte 2004).
Life History, Abundance, Activity, and Special Behaviors
The genus Nycibatrachus has a wide range of reproductive behaviors. However, all species are known to deposit eggs on rocks or vegetation that hangs over water. The tadpoles hatch out and fall into the water where they develop until metamorphosis (Willaert et al. 2016).
Nyctibatrachus humayuni is a stream-breeder. Both males and females call, although the latter is rare and of unclear function. Males call from territories that may be partly submerged, but usually are on rocks, vegetation and fallen trees bordering or overhanging the stream; territories were observed up to 4 m above water. Males have strong site fidelity and will guard multiple clutches in the same location (Willaert et al. 2016).
Male advertisement calls have two distinct parts. The first is non-pulsated and the second is pulsated with a temporal structure. The overall call time ranged from 483 - 630 seconds, reached their full amplitude in the middle of their call and with a dominant frequency range of 1.11 - 1.45 kHz. The range of dominant frequency for the first portion of the call was 0.91 - 1.45 kHz and the second was 1.17 - 1.47 kHz. The pulsed portion of the call consisted of 16 - 24 pulses with an average pulse period of 13.2 milliseconds and duration of 12.8 milliseconds, and pulse rates between 74 - 84 pulses per second. The mean rise time of the pulses were 4.7 milliseconds and the mean fall time was 8.1 millisecond. Within an individual, there was relatively low variation between calls. Additionally, there was frequency modulation for the first portion of the call but not for the second (Willaert et al. 2016).
Females were occasionally heard using a call that was distinct from male advertisement calls. Two females were observed calling after trying unsuccessfully and for a considerable amount of time to reach a male. On one instance a male was observed moving closer to the female but the female was still unable to find the male. Males were observed changing their direction to be towards calling females and to increase their vocalization rate leading researchers to speculate that female calls help the frogs locate each other. However female calling may serve other functions that require testing. A single female, calling from 2.5 m above the ground for over 30 minutes (50 calls), was recorded and her call described. Her calls, which was similar to other female calls, consisted of a single unpulsed note lasting a mean duration of 83 milliseconds with several frequency peaks. The lowest three frequency peaks had mean dominant frequencies of 1.45 kHz, 2.90 kHz, and 4.37 kHz (Willaert et al. 2016).
Nyctibatrachus humayuni is known for having a unique breeding method that results in a 100% fertilization rate. Females move between male territories before choosing a male to mate with. The female then approaches the male and backs up to him until her abdomen is touching his head. The male then mounts the female in a loose form of amplexus, termed a "dorsal straddle". During the dorsal straddle the male rests above the female by holding on to vegetation above the female (or occasionally resting his hands on her arms or hands) and lays his abdomen on her lower dorsum. The male then pulses his flanks for 338 - 1670 seconds while mounted, at which time it is believe that he deposits sperm the female's back. To signal for dismounting, the female arches her back repeatedly and the male dismounts. Within a few seconds, the female lays her full clutch without any further physical contact with the male. After depositing her eggs, the female remains motionless in her ovipositioning stance with her legs around the eggs for 260 - 961 seconds, at which time it is believed that the sperm spreads from her back onto her legs and over the eggs. The female stays with her clutch for a few more minutes after that before jumping back into the stream. The male stays with the female during this whole process but does not come into contact with her after dismounting. The unique dorsal straddle is speculated to function as a means to avoid falling and thus interrupting mating (Willaert et al. 2016).
Although males attend eggs, egg clutches have a high (80%) predation rate, most frequently by snakes. The eggs begin to hatch 18 - 19 days after oviposition and take 1 - 2 days to complete. The hatched larvae immediately fall into the water below where they continue their development (Willaert et al. 2016).
Trends and Threats
The population is vulnerable and declining, due mainly to habitat loss and pollution. It is currently protected by national legislation and protected within the Koyna and Bhimashankar Wildlife Sanctuaries in the state of Maharashtra (Stuart et al. 2008).
Possible reasons for amphibian decline
General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Subtle changes to necessary specialized habitat
Local pesticides, fertilizers, and pollutants
Long-distance pesticides, toxins, and pollutants
Nyctibatrachus humayuni is named after Mr. Humayun Abdulali of the Bombay Natural History Society who first discovered the frogs at Khandala, India and collected tadpoles from other locations (Bhaduri and Kriplani 1955).
Bhaduri, J.L., and Kriplani, M.B. (1955). ''Nyctibatrachus humayuni, a new frog from the Western Ghats.'' Journal of the Bombay Natural History Society, 52, 852-859.
Busse, K. (1991). ''Bemerkungen zum fortpflanzungsverhalten und zur Zucht von Rhinoderma darwinii.'' Herpetofauna, 13, 11-21.
Crump, M. (1972). ''Territoriality and mating behavior in Dendrobates granuliferus (Anura: Dendrobatidae).'' Herpetologica, 28, 195-198.
Kunte, K. (2004). ''Natural history and reproductive behavior of Nyctibatrachus cf. humayuni (Anura: Ranidae).'' Herpetological Review, 35, 137-140.
Limerick, S. (1980). ''Courtship behavior and oviposition of the poison arrow frog Dendrobates pumilio.'' Herpetologica, 36, 69-71.
Stuart, S., Hoffmann, M., Chanson, J., Cox, N., Berridge, R., Ramani, P., and Young, B. (eds) (2008). Threatened Amphibians of the World. Lynx Edicions, IUCN, and Conservation International, Barcelona, Spain; Gland, Switzerland; and Arlington, Virginia, USA.
Willaert B, Suyesh R, Garg S, Giri VB, Bee MA, Biju SD (2016). ''A unique mating strategy without physical contact during fertilization in Bombay Night Frogs (Nyctibatrachus humayuni) with the description of a new form of amplexus and female call.'' PeerJ, 4, e2117.
Written by Alamelu Natesan (amluuu AT gmail.com), UC Berkeley
First submitted 2008-03-12
Edited by Kellie Whittaker, updated by Ann T. Chang (2016-06-19)
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