Bombay Night Frog
© 2011 Bert Willaert (1 of 1)
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
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
There is no amplexus in this species, making N. humayani the only known Old World frog species to completely lack amplexus. This is very unusual; only two other anuran groups (Dendrobatidae and Rhinodermatidae) have species which do not engage in any form of amplexus (Crump 1972; Limerick 1980; Busse 1991). Unlike dendrobatids and rhinodermatids, N. humayani has larger clutches and does not exhibit parental care. Surprisingly, N. humayani achieves 100% fertilization even in the absence of amplexus (n=85 clutches, totaling 1,937 eggs; Kunte 2004).
The breeding season starts with the beginning of the southwest monsoon, by the end of May to early June, and continues until mid-September. Rain and monsoon seasons lead to short peaks in breeding. Males perch up to a meter high on leaves overhanging flowing water of steep, rocky forest streams. If overhanging vegetation is not present, they resort to perching on wet, slanted, moss-less rock faces adjacent to the stream. Calling sites are spaced approximately 5-8 m apart, with some further apart. Vocalizations are used both for advertisement to females and for territorial defense as well, since a single male exclusively claims a large territory with several suitable calling posts that later serve as oviposition sites. If competition arises, the larger male is always dominant (Kunte 2004).
Nyctibatrachus humayuni is similar to the centrolenids (glass frogs) in depositing eggs mainly on vegetation overhanging water. Males vocalize from leaves that are 10-100 cm above the stream, or from the moss-free rocks adjacent to the stream (thus some eggs may be deposited on streamside rock surfaces as well). Females search through several male territories to choose a male. As the female approaches the chosen, vocalizing male, his calls get more frequent. The male steps to the side and continues to vocalize while the female deposits her eggs at the exact calling site. If she deposits part of the clutch at a second location, it is always the spot a few centimeters away where the male moved after her arrival. Thus, the male determines the oviposition site since the female follows his vocalization to release her clutch of eggs Immediately after the clutch is released, the female returns back to the water and the male ceases calling and positions himself to fertilize the eggs. After fertilization, the male resumes his calling at a new site a few centimeters away (on the same branch, often on the same leaf), until he is encountered by a different female. Clutches fertilized by the same male are thus spatially clustered (Kunte 2004).
Females lay at least two and potentially up to six clutches per breeding season, with 10-55 eggs in each clutch. Each newly laid egg measures 2.5-3 mm in diameter. After about 12-15 days of development, tadpoles hatch by aggressively wriggling in the egg-jelly, which bursts and releases them into the flowing water underneath. There is no parental care for this species (Kunte 2004).
It is thought that reproductive success is approximately equal between the sexes in this species, since most calling males typically succeeded in attracting multiple females, and females lay multiple clutches. This may contribute to the lack of sexual dimorphism for N. humayuni (Kunte 2004).
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
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.
Written by Alamelu Natesan (amluuu AT gmail.com), UC Berkeley
First submitted 2008-03-12
Edited by Kellie Whittaker (2010-01-13)
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