Nyctibatrachus major

Illustration of N. major from the 1882 description

The zoologist George Albert Boulenger formally described the species as Nyctibatrachus major in 1882 on the basis of twelve type specimens from "Wynaad" and "Malabar".[3][4] It is the type species of the genus Nyctibatrachus.[5] In 2011, the herpetologist S. D. Biju and colleagues re-examined the specimens from which the species was described, and concluded that several of these actually represented species distinct from N. major; they then designated an adult female collected from "Malabar" the lectotype to avoid subsequent taxonomic uncertainty.[4] In 1910, zoologist Nelson Annandale described the species Rana travancorica on the basis of specimens collected from Travancore;[6] this species was synonymised with N. major by the herpetologist R. S. Pillai in 1978.[2] Although this syonymisation was disputed by the herpetologist S. K. Dutta in 1997, it has since been found to be valid and R. travancorica is currently treated as a synonym of N. major.[2][4]

There are no subspecies of N. major.[2] It is currently treated as one of 34 species in the night frog genus Nyctibatrachus, in the robust frog family Nyctibatrachidae.[5] Within the genus, it is sister (most closely related) to a clade (group of organisms descending from a common ancestor) formed by N. acanthodermis and N. gavi. These three species are further sister to a clade formed by N. grandis and N. sylvaticus. The clade of these five species is sister to N. radcliffei, and these six species are sister to N. indraneili.[7][8] Some studies have found a slightly different relationship, with major being sister to gavi, and acanthodermis being sister to that clade.[9] The following cladogram shows relationships within this clade based on a phylogeny by a 2017 study:[7]

The species has had its DNA barcoded.[10]

N. major is a large species of night frog, with an adult snout–vent length of 31.5–52 mm (1.24–2.05 in) for males and 43.7–54.2 mm (1.72–2.13 in) for females.[4][11] The upperside is dark greyish-brown, with variable light grey and dark brown markings, while the underside is grayish-white. The lores and area around the tympanum (external ear) are dark brown, with a dark grey stripe between the eyelids, and the irises are dark brown. The sides of the stomach are light grey, mottled with white and dark grey, while the groin is dark brown. The limbs are brown with pale diagonal bands. When preserved in 70% ethanol, the colour of the upperside changes to greyish-brown, marked variably with pale and dark brown. The colour of the band between the eyelids changes to faint grey, and the underside and sides become whitish, the latter marked with black spots.[4] Males and females are broadly similar in their external appearance, but can be distinguished by the presence of the femoral glands (bulbous glands near the inner thigh) in males.[11]

The species can be distinguished from other species in its genus by its large size; well-developed toe and finger discs; the absence of a groove on the third finger disc; the presence of a groove on the fourth toe disc; conspicuous wrinkling and glandular protrusions on the skin of the upperside; medium-sized webbing between the fingers; and a prominent Y-shaped ridge from the upper lip to the nostrils.[11]

The species is endemic to the Western Ghats of southern India, where it is found in Kerala, Tamil Nadu, and Karnataka.[12] It was previously thought to also occur in Maharashtra, but those records are likely erroneous.[14] Adults inhabit fast-moving streams in evergreen deciduous forest, secondary forest, and forest edge at elevations of 0–900 m (0–2,950 ft).[1][12] They prefer undisturbed forest,[15] and generally are not found in highly degraded habitats[1] or in open areas near the boundary of a forest.[16] In particular, streams inhabited by adults are slight acidic (pH of 6.0–6.5),[11] with low temperatures, light intensities, and low concentrations of calcium carbonate, as well as high levels of dissolved oxygen.[15] Tadpoles also have highly specific requirements for their microhabitat, preferring streams with low air and water temperatures, low light intensity and dense canopy cover, high humidity, and large amounts of leaf litter.[16] Tadpoles have been found at elevations up to 825 m (2,700 ft).[12]

Adults are mostly nocturnal and spend most of their time in aquatic environments, most commonly being seen on rocks near water. During the day, adults typically conceal themselves below rocks, while subadults are more active. When disturbed or threatened, it rushes into the mud of the streambed and stays underwater for some time before coming to the surface again.[12]

Diet

N. major feeds on several species of frog, such as Fejervarya limnocharis (pictured)[17]

N. major mainly feeds on insect larvae and other frogs. Insects known to be consumed include dragonflies in the genus Ophiogomphus, beetles in the genera Psephenus and Enochrus and the families Dytiscidae and Haliplidae, true bugs in the genus Neides, and springtails in the genus Sminthurinus. Frogs that N. major feeds on include Fejervarya limnocharis, Euphlyctis cyanophlyctis, and Micrixalus saxicola; the especially high rates at which the species predates F. limnocharis and E. cyanophlyctis may be due to the fact that these two species inhabit the same microhabitat as it.[17]

N. major is classified as being vulnerable on the IUCN Red List due to its small and fragmented range and ongoing habitat degradation.[1] It is threatened by habitat loss caused by factors such as deforestation, wood and timber harvesting, and conversion of land to agriculture. It is also threatened by the construction of check dams, road construction, and an increase in tourism in its range. Adults and tadpoles of N. major are highly sensitive to changes in their microhabitat.[15][16] Consequently, increased human activities that alter their habitat may lead to declines in the species' population, as has occurred in the related N. aliciae.[16]

N. major may also be threatened by nitrate pollution caused by overuse of fertilisers. Due to habitat fragmentation, many of the streams the frog inhabits are adjacent to farms which experience high levels of nitrogen-based fertilizer use, leading to elevated nitrate concentrations in the water. The LC50 (concentration at which 50% of exposed tadpoles die) for nitrates in the species is 2510 micrograms (μg) per litre over a 30-day period; nitrate concentrations in streams with N. major tadpoles have been collected vary from 110 to 6000 μg per litre. Even sub-lethal concentrations of nitrates in the water lead to adverse effects such as paralysis, restlessness, abnormal swimming patterns, and swollen body parts.[19][20]