Description

Nyctibatrachus petraeus has a short body and blunt snout. Calling males have a snout-vent range of 32 – 47 mm and adult females have a range between 37 – 45.5 mm. The head is wider than it is long, with a head width to length ratio of 1.55. The head slopes forward in the lateral view. The snout has a narrow longitudinal fold that comes from the upper lip to the nostrils and then branches into two forks. The nostrils are oval shaped and are positioned close to the tip of the snout. The canthus rostralis is weak and the interorbital width is more than twice the upper eyelid width. The eyes are large and the contracted pupils in this species are rhomboidal. The length of the anterior margin of eye to nostril is larger than the internarial distance. A transverse fold connects the two upper eyelids. The tympanum is indistinct. The mouth extends to the posterior corner of the eye. Nyctibatrachus petraeus has maxillary teeth present and has a notch in the anterior edge of mandible that is vaguely shaped like a “W”. The bifid tongue is triangular in shape, covered in papillae and is free posteriorly. The choanae is located close to anterior edge of palate. The vomerine ridges are large in this species and appear in two series that begin at the beginning of the choana and are separated from one another by a distance that is 1/3 of vomerine ridges length. Each cluster of vomerine ridge has 11 teeth. The skin is not co-ossified to the boney elements of the head and the pineal ocellus is absent. The dorsum has transverse skin folds. Suprecloacal folds and postcoacal tubercles are not present in this species however, there are small glandular structures on the rectal region (Das and Kunte 2005).

The arms are short and stout. The fingers are long and stout and lack interdigital webbing. The relative lengths of the fingers are: III > IV > II > I. The tips are dilated into disks with circummarginate grooves. The disk on the third finger is the widest. Rounded subarticular tubercles are prominent on all fingers. Palmar tubercles are present. The hind legs are also short and stout and do not overlap when folded on a right angle to the axis of the body. There is a postaxial fold on the heels and the femoral glands are present. The outer metatarsal tubercle is absent, and the elongated inner metatarsal tubercle is slender. The toes are long and thin. There is webbing between all the toes expect for the fourth toe. The relative toe lengths are: IV > III > VI > II > I. The rounded tips of the toes have circummariginal grooves and the toes have subarticular tubercles that are well developed. Disks on fingers and toes are similar in width (Das and Kunte 2005).

Nyctibatrachus petraeus is most likely to be confused with to P. humayuni, especially due to the close geographical proximity of the two species. In 2005, Das and Kunte split N. petraeus from N. humayuni based on morphology. Nyctibatrachus humayuni is most notably different because it has a snout that does not project beyond the mouth, a snout with a length equal to the length of the eye, vomerine teeth patches that contain approximately 6 - 8 teeth, and adults are larger, approximately 48 mm. Among other Nyctibatrachus, N. petraeus can be differentiated from N. aliciae by the latter's well defined supratympanic fold, presence of outer metatarsal tubercle, presence of webbing on toe IV between the middle and distal tubercles and the pattern on the dorsum that is brown and tan with light banding. Nyctibatrachus beddomii varies from N. petraeus because it has a smaller body size, has a smooth dorsum, has slender, unwebbed toes, lacks circummariginal grooves, and has a light blue-whitish stripe behind and below the eyes. Nyctibatrachus deccanensis can be contrasted from N. petraeus by the former's short snout, irregular dorsolateral folds, fingers and toes lacking enlarged disks, and presence of toe webbing that can reach middle subarticular tubercle in some individuals. Nyctibatrachus hussaini can be differentiated by N. petraeus because of its large body size, distinct supratympanic fold, presence of dermal fold that extends from the lower eyelids along the jaw, vomerine teeth in rows of about 8 - 9 teeth, and light thumb pads in males. Nyctibatrachus kempholeyensis is more easily differentiated because the dorsum is a bronze or black colored, the throat of males are yellow, the iris is red, the skin lacks folds and males have large external vocal sacs. Nyctibatrachus major is unique from N. petraeus by the former's shallow digital disks, poorly defined circummarginal grooves, lips with narrow white stripes and a dorsum with light dorsolateral bands. Nyctibatrachus minor has a dorsolateral glandular fold, lacks toe webbing, and has no femoral gland in adult males. Nyctibatrachus sanctipalustris is unlike N. petraeus because it has toe webbing to the middle subarticular tubercle, no canthus rostralis, and has a reddish-brown dorsum. Nyctibatrachus sylvaticus has a broader head, lower lips that are barred, a visible tympanum, toe webbing that reaches middle subarticular tubercle, and a inner metatarsal that is spade shaped that allow for differentiation from N. petraeus. Lastly, N. petraeus differs from N. vasanthi by the latter having smooth dorsum skin, vomerine teeth row in the shape of an oval, disks on finger that lack circummarginate grooves, subarticular tubercles are that indistinct, flanks with dermal folds and toes that are webbed to the base of disks (Das and Kunte 2005).

In life, the dorsum is a medium brown and has a grayish-brown saddle that starts from the interorbital region and extends to the vent. The fore- and hind limbs are medium brown and have grayish-brown stripes. The pupils are black and have a golden-yellow sclera. The juvenile had extensive light orange markings and have an interorbital bar along with another bar across rostrum and edges of dorsal saddle. The throat is cream (Das and Kunte 2005).

In preservative, the dorsum of Nyctibatrachus petraeus is medium brown in color and has a darker brown saddle shaped splotch that stretches from the interorbital to sacral region. The throat is a brown color. There are no light dorsolateral bands present and the venter has a uniform cream color. The fore- and hind limbs are the same medium brown color and have dark brown striping. The thighs have light orange markings and the under surface of the upper arm is cream. The under surfaces of the thighs are a light brown. The tongue is pinkish-yellow (Das and Kunte 2005).

Nyctibatrachus petraeus is slightly sexually dimorphic. Males can be distinguished from females and juveniles by the presence of elongated femoral glands on the inner side of the thighs. Males lack external vocal sacs and show internal vocal sacs, with openings on each side of the tongue (Das and Kunte 2005).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: India

View distribution map in BerkeleyMapper.

Nyctibatrachus petraeus is found in Castle Rock located in the Western Ghats of southwest India at elevations around 300 m a.s.l. Individuals are commonly found besides rocky flowing streams through semi-evergreen forests, with hilly terrain with steep slopes (Das and Kunte 2005).

Life History, Abundance, Activity, and Special Behaviors

There is no amplexus in this species, making Nyctibatrachus petraeus the only known Old World frog species to completely lack amplexus and because of this, males lack nuptial pads. This is very unusual; only two other anuran groups (Dendrobatidae and Rhinodermatidae) have species that do not engage in any form of amplexus (Crump 1972; Limerick 1980; Busse 1991). Unlike dendrobatids and rhinodermatids, N. petraeus has larger clutches and does not exhibit parental care. Surprisingly, N. petraeus 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 (Kunte 2004).

The call has been described as a soft and melodious, prolonged note—“OORRsss”— with an occasional faint “OA” preceding the call. Male 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, Das and Kunte 2005).

Nyctibatrachus petraeus is similar to members of the family Centrolenidae (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 (Kunte 2004).

Although, there was no amplexus or any physical contact between the sexes, it has been observed that there is ‘pseudo-amplexus’. This preceded oviposition by 5 min and therefore did not serve the purpose of fertilization (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 (Kunte 2004).

Trends and Threats

Nyctibatrachus petraeus is naturally found in the forests of the Western Ghats and this area has historically been devastated by habitat destruction. This loss continues today, primarily due to conversion to agricultural lands, especially due to the prevalence of eucalyptus plantations, coffee and tea plantations. However, Nyctibatrachus petraeus is listed as "Least Concern" because it is a relatively common species with a sizable range, and thus presumably there is a large population. It also occurs in several protected areas, such as Dandeli and Bheemgadh Wildlife Sanctuaries, is tolerant of closed-canopy secondary forest, and is not known to be declining (Kunte 2006).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Urbanization
Prolonged drought
Drainage of habitat
Dams changing river flow and/or covering habitat

Comments
The species authority is: Das, I., Kunte, K. (2005). "New species of Nyctibatrachus (Anura: Ranidae) from Castle Rock, Karnataka State, Southwest India." J. Herpetol. 39:465-470.

In 2005, Das and Kunte split N. petraeus from N. humayuni based on morphological differences. However, molecular analysis was not done to determine if the two species were sister species.

The name of this species comes from the Greek "petraeus" for “rock ", after the type locality, Castle Rock, as well as referring to the rocky substrate of the collection locality (Das and Kunte 2005).

References

Das I, Kunte K (2005). ''New species of Nyctibatrachus (Anura: Ranidae) from Castle Rock, Karnataka State, Southwest India.'' Journal of Herpetology, 39(3), 465-470. [link]

Kunte, K. (2004). ''Natural history and reproductive behavior of Nyctibatrachus cf. humayuni (Anura: Ranidae).'' Herpetological Review, 35, 137-140.

Kunte, K. (2006). ''Nyctibatrachus petraeus''. The IUCN Red List of Threatened Species 2006: e.T61866A12568499. http://dx.doi.org/10.2305/IUCN.UK.2006.RLTS.T61866A12568499.en. Downloaded on 22 April 2019.

Species Account Citation: AmphibiaWeb 2019 Nyctibatrachus petraeus: Castle Rock Night Frog <https://amphibiaweb.org/species/6654> University of California, Berkeley, CA, USA. Accessed Apr 19, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 19 Apr 2024.

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