Description
Philautus nepenthophilus is a medium-sized frog described from two adult females and six adult males. Females have an snout-vent length range of 35.22 - 37.24 mm and males have a snout-vent length range of 28.67 - 32.34 mm. The head is moderately large, rounded, and slightly longer than wide. It ranges in length from 10.53 - 11.5 mm and in width from 10.38 - 13.90 mm. The head is about two-fifths as long and about one-third as wide as the snout-vent length. Viewed dorsally, the snout is slightly mucronate (coming to a sharp point) or truncate and occupies about two-fifths of the overall head length. In profile, the snout is vertically truncated but not mucronate, and does not project over the lower jaw. The snout length and eye diameter are nearly equal, with snout length ranges from 3.76 - 5.11 mm and eye diameter ranges from 3.87 - 5.12 mm. The nares are slightly raised, oval, and possess flaps of skin. The distance between them is smaller than the distance to the eyes. The internarial distance ranges from 1.60 - 2.48 mm and the eye to nares distance ranges from 1.98 - 2.95 mm . The canthus rostralis is short, distinct, and rounded. Dorsally, it appears somewhat curved. The interorbital distance is about twice as long as the eye diameter and ranges from 3.19 - 4.85 mm. The eyes are small compared to the head and have horizontal pupils. The area immediately surrounding the eyes (lores) is only weakly concave, and the tympanum is not very distinct either. The tympanum diameter is large, about two-fifths of the eye diameter, and ranges from 1.81 - 2.46 mm. Above it, the supratympanic ridge is distinct and straight. The dorsum is covered with smooth skin. However, scattered across the head, snout, and eyelids are finely granulated, tiny, white-transparent tubercles. These tubercles have pointed keratinous tips only visible under magnification. The venter is granular in appearance (Etter et al. 2021)

The forelimbs are slender and end in large hands, which are about 1.39 times the forelimb length and are about one-third the snout-vent length. The forearms are 5.58 - 8.8 mm long and the hands are 9.73 - 12.19 mm long (measured from the tip of the 3rd finger to the proximal end of the palmar tubercle). Finger length is as follows: III > IV > II > I. The fingers are tipped with rounded discs and lack any webbing. The hands’ subarticular tubercles are only weakly distinct, while the metacarpal tubercles and forearm tubercles are absent. Finally, males lack nuptial pads on their digits (Etter et al. 2021).

The hind limbs are very long and slender, ranging from 50.17 - 64.14 mm in length, about 1.5 times the snout-vent length. The tibias are especially long; they are half as long as the snout-vent lengths, longer than the feet, and slightly longer than the thighs. The thighs range from 13.57 - 15.09 mm in length, the tibia range from 14.65 - 19.26 mm, the tarsi (measured from the tibiotarsal articulation to the proximal inner metatarsal tubercle) range from 8.12 - 10.79 mm, and the feet (measured from the proximal inner metatarsal tubercle to the tip of the 4th toe) range from 13.24 - 17.2 mm. The outer metatarsal tubercle is absent, but the inner metatarsal tubercle is small and oval. The toes have rounded discs, with the discs of toes IV and V ranging from triangular to oval in shape. Toe length is as follows: IV > V > III > II > I. Webbing on the toes is moderate in extent, typically reaching two-thirds of the toe length. The feet possess tubercles, but these are generally absent or weakly distinct. The subarticular tubercle is barely distinct and rounded. There are no tubercles on the tarsus or heel (Etter et al. 2021).

DIAGNOSIS:

Philautus nepenthophilus adults possess eight morphological and behavioral characteristics that, in combination, distinguish them from other members of their genus. (1) In life, the head, dorsum, and flanks are a uniform yellow to green color without any distinct patterning. (2) Individuals vary little in color pattern. (3) The skin is largely smooth with only minute tubercles scattered across the eyelids, interorbital region, and sometimes the snout. (4) The snout is truncated, rounded, and short (whereas the snouts of other congeners are often more pointed). (5) There is no sexual dimorphism in head shape. (6) The tympanum is fairly large. (7) Generally, this is a medium-sized frog compared to other members of its genus, most of which are smaller. (8) The advertisement call is distinctly fast, rattling, and short. Each of the three call notes has 6 - 7 pulses and lasts for about 36.33 ms, with a dominant frequency of 2812.5 Hz (Etter et al. 2021). Philatus nepenthophilus can be specifically distinguished from some other Philautus species as follows: Philatus acutus is smaller, darker, and has a red iris and a more widely-curved canthus rostralis. Its call contains more notes that are longer and higher in pitch. Philatus amoenus is smaller and has banded lips, a smaller tympanum diameter, and more tubercles on its skin (some of which form a distinct line from eye to dorsum and others that are clustered on the metatarsals). Notes in P. amoenus’ call are longer in duration, produced more frequently, and lower in pitch. Philatus aurantium is smaller and has a darker tympanum and bright orange marks on its thighs. Its call has many more notes, each longer in duration. Philatus bunitus is larger with a striking green-and-black color pattern and possesses vomerine teeth (which P. nepenthophilus lack) and yellow webbing between its digits. Its call contains more notes and is of a lower pitch. Philatus davidlabangi is approximately equal in size, but is darker in color, and its nares are closer to its eyes. Its canthus rostralis is curved sharply, its tubercles are curved in a row from the eye to the sacrum, and its dorsum possesses an X-shaped mark. Its call has only one long note. Philatus disgregus is much smaller, has noticeable conical tubercles on the upper eyelids, and is colored black-and-white below the eye. Philatus erythrophthalmus is smaller and has lingual papillae, a red iris, a less distinct tympanum and supratympanic ridge, pinkish digit-tips, and a bright yellow-golden groin. Philatus everetti is slightly larger, beige in color, and has a rounded snout, vomerine teeth, a pale golden iris, a smaller tympanum, conical tubercles below the anus and along the limbs, a flap of skin on the edges of the limbs, and finely granulated skin. Philatus gunungensis is smaller and has a steeper snout when viewed in profile, bright yellow thighs, and more distinct subarticular, thenar, and palmar tubercles. Its call contains more pulses and is continuously emitted. Philatus hosii is notably larger and possesses two series of vomerine teeth, a longer snout, a bright green iris, dark marks on the hind limbs, and a faint “X” on its dorsum. Philatus ingeri differs strongly by its split iris coloration, which is pale gray above and dark brown below. This color pattern is also present on its face to the tip of the snout, which is longer and sharply pointed. Its heels bear spiny tubercles. Philatus juliandringi is smaller and the males have nuptial pads. Its call is just one note long and has a higher dominant frequency. Philatus kakipanjang is smaller and has a concealed tympanum, a long and thick supratympanic ridge, and small but prominent nuptial pads. Its call is only one note in length and slightly lower in pitch. Philatus kerangae is obviously patterned with a light green dorsum and upper limbs with brown markings and a pale venter with brown splotches. It has vomerine teeth and tubercles on its heels. It calls at a lower frequency and emits more notes per call. Philatus larutensis has a row of tubercles on the lower jaw, a fleshy tubercle on the rostrum of the females, and strongly-developed nuptial pads in males. Philatus macroscelis has two groups of vomerine teeth, a less pointed snout, conical tubercles on the upper eyelids, small tubercles on the outer edges of the limbs, and dark crossbars on the limbs. Philatus mjobergi is smaller and has a relatively wider head, nuptial pads, and tubercles on its heels. Its call features more notes with a slightly higher frequency. Philatus nephophilus is smaller and has a red iris, a more pronounced supratympanic fold with an orange stripe, nuptial pads, and tubercles on its heels. Its call has more notes each of longer duration. Philatus refugii is much smaller and the females have a tubercle on the rostrum. The males have nuptial pads. They also have an inverted “V”-shape pattern on the dorsum, and the thighs have brown bars in the anterior region. Philatus saueri is smaller and has a protruding snout, a light interorbital stripe, a steeply-curved supratympanic fold, and a reticulated dark gray pattern on the limbs and sides of the dorsum. Philatus tectus is smaller and has a dark brown iris, a small dorsal tubercle close to the eye, a canthus rostralis curved at a large angle, and large nuptial pads. Finally, P. umbra is dark brown to gray and has lingual papilla, a black iris scattered with gray, a sharply angled canthus rostralis, and rudimentary nuptial pads (Etter et al. 2021).

COLORATION:

In life the body is ocher, yellow-orange-brown, or greenish, and speckled light brown. The dorsal spots are larger and more unevenly distributed than those on the abdomen. The black-and-orange irises are marbled with gold. The eyelids are a dark, green-tinted ocher with light brown speckles. Compared to the body, the tympanum is only slightly lighter in color and possesses fewer brown spots. The supratympanic ridge features a dark brown band. The smooth throat lacks a noticeable pattern. The venter has a white areolated pattern while the flanks have white spots.The forelimbs are more orange in color whereas the hind limbs are browner and darker. The tips of the fingers and toes are the same color as the dorsal spots. The toe webbing is clear with a whitish tinge (Etter et al. 2021).

When preserved, the frog is pale brown, with lighter sandy-white areas on the flanks and venter. The white areolate pattern remain visible. Some dark brown areas, such as the dorsal spots and canthal band, are hardly visible in preservation. The eyelids acquire a dark gray color and the tips of the fingers and toes become a deeper brown, matching the forehead and snout (Etter et al. 2021).

VARIATION:

Variation is described from the type series designated by Etter et al. (2021). The snout varies from being truncate (with the nostrils at the anterior-most point) to mucronate (with the small snout tip at the anterior-most point). The nares can be circular, oval, or drop-shaped. In some specimens, the canthus rostralis is not strongly distinct. The shape of the supratympanic ridge varies from being curved to the arm insertion to instead forming a straight line. Sometimes, toe III is equal in length to toe V instead of being smaller. The discs present at the tips of the digits range from round to approximately triangular. Variation in toe webbing is denoted in brackets in the following formula: I (1.75–2.25) – (2–2.5) II (1.25–1.5) – (2–3) III (1–1.75) – (2.75–3) IV (2.5–3.25) – (1.25–2) V. As for the skin, its tubercles vary from being obvious to hardly visible. Tubercles on the head vary from being lightly speckled across the interorbital region to blanketing the entire dorsal surface of the head (snout, interorbital region, eyelids, and head). On the extremities, the tubercles are especially variable: the outer metatarsal tubercle varies from being oval, round, hardly visible, to entirely absent. Some individuals may have metacarpal tubercles or reniform metatarsal tubercles. Additionally, some possess a weakly distinct thenar tubercle (Etter et al. 2021).

Specimens vary from pale brown, to ocher, to yellow-green. The iris is generally marbled with gold, dark orange, and black, sometimes with a greenish tint. The brown band on the supratympanic ridge varies in distinctiveness from highly visible to inconspicuous. On some individuals, the brown dorsal spots may contrast strongly with the base color, while on others, they may be barely visible. Sometimes, the spots may form a vague “W” in the interorbital region, and on the hind limbs, they may form indistinct bands (Etter et al. 2021).

Finally, the species is sexually dimorphic in size. Females are larger in snout-vent length, 35.22 - 37.24 mm in females vs 28.67 - 32.34 mm in males, and lack a vocal sac opening. In females, the variation in the ratios of head width to length, internarial to eye-to-nostril distance, interorbital to eye diameter, and interorbital to internarial distance are smaller than in males, while the variance in the foot to tarsus length ratio is greater (Etter et al. 2021).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Malaysia

View distribution map in BerkeleyMapper.

Philautus nepenthophilus is known from the Malaysian state of Sarawak on the island of Borneo. It has only been reported from the type locality of Church Camp in Pulong Tau National Park at an elevation of 2,115 m a.s.l. (Etter et al. 2021). Church Camp is located on Gunung Murud, the highest mountain in Sarawak, which features undisturbed mossy forests (Hertwig et al. 2014). Specifically, P. nepenthophilus has been reported from the edges of montane Kerangas forest (Etter et al. 2021), a forest type characterized by acidic, sandy podzol soils and vegetation adapted to water stress (Miyamoto et al. 2016).

Life History, Abundance, Activity, and Special Behaviors
All observed individuals of P. nepenthophilus were found at night in montane Kerangas forests. They closely associate with Nepenthes mollis, a pitcher plant that grows in these forests. They are often perched near or on the upper pitchers of the plant. Individuals will dive into the liquid inside the pitchers if disturbed (Etter et al. 2021).

Males will perch on the pitchers of N. mollis and make a fast, short, rattling advertisement call series. The series is composed of five calls, and each call contains three notes. The average call duration is 164.4 milliseconds (ms), whereas the average note lasts 36.33 ms. The dominant frequency in the call is 2812.5 Hz. Each note is marked by one to two fading low frequency pulses. The second and third notes start with pulses that increase in amplitude, and the highest frequency is observed in the third note of the call. On average, each note contains six to seven pulses. Additionally, the call is non-continuous, containing a noticeable inter-call interval (Etter et al. 2021).

Philautus nepenthophilus is oviparous, with internal fertilization, and has indirect development. Eggs are laid in the phytotelmata (fluid-filled cavities) of the rare endemic pitcher plant N. mollis. It is unclear if P. nepenthophilus lays its eggs solely in N. mollis or if it uses other bodies of water. The clutches are small, and the eggs are unusually large. As described by Etter et al. (2021), a female specimen had three fertilized eggs ranging from 5.4 mm to 7.5 mm in diameter. This size is comparable to the diameter of eggs found in directly developing frog species. The female also had several smaller, less-developed eggs, which suggests that several clutches are produced every year (Etter et al. 2021).

Philautus nepenthophilus is not known to have aposematic body coloration (Etter et al. 2021).

Larva
Larval descriptions by Etter et al. (2021) focused on later Gosner stages 35 -38. The largest and most developed tadpole collected have a maximum total length of around 21.55 mm. The larval body has an inverse pear-shape, with a head broader than the trunk. The body is the widest at the anterior to an obvious constriction between the head and trunk. Additionally, the body is dorsoventrally compressed to a roughly uniform depth. A stubby rounded snout bulges in the center of the face. The slightly sunken nostrils face anterolaterally and are on the very end of the snout. Moreover, a orbitonasal streak is clearly visible. The eyes are dorsolateral and do not extend beyond the head when viewed from above. The eye axis is oriented anterolaterally, which suggests good frontal vision. The ventrally-located mouth is relatively reduced and hard to see without magnification. It is missing keratodonts and an oral disc. However, the mouth has thin lips with two lateral papillae on each side, which may be remnants of an oral disc. Additionally, the mouth sits anteriorly or in a depression in the ventral gular region. Although still unproven, this placement may assist in attaching to pitcher walls. The labial tooth row formula is 0/0. There are highly reduced keratinized jaw sheaths that are visible only under a microscope. The spiracle is sinistral, positioned ventrally, and directed posteriorly. The medially-located spiracular orifice is fused with the body wall and does not protrude freely. The anal tube opens sinistrally and runs along the ventral fin. A circular, transparent posteroventral skin flap can be found between the abdomen and tail, merging dorsally with the ventral tail fin. The base of the moderately-developed tail is around 56% of the body height and 45% of the body width. The upper and lower tail fins are of equal height and begin at the junction between the body and tail and run mostly parallel to the tail. This creates a tail whose maximum height is about one-third its length. The fin tip is smoothly curved. Lastly, tadpoles also have a distinctive yolk sac in their gut, which can be seen through the abdomen at any developmental stage (Etter et al. 2021).

Diagnosis:

The most distinctive features of P. nepenthophilus tadpoles include a small oral orifice, a short snout, reduced mouthparts, a posteroventral skin flap, and a large yolk sac. Tadpoles of P. nepenthophilus may be confused with the tadpoles of the sister species Philautus macroscelis since both have a small snout and reduced mouthparts. However, only P. nepenthophilus has a posteroventral skin flap and scattered iridophores in the eyes. Philautus macroscelis is also larger, less broad, and has anterolaterally positioned nares (Etter et al. 2021).

Coloration:

In life, the tadpoles are generally dark brown to gray dorsally, extending from the head to the end of the tail. This coloration fades posteriorly and ventrally. Other than unpigmented orbitonasal streaks, they have no clear markings or patterns. Ventrally, there is fine pigmentation on the throat and mouth. Otherwise the tadpoles have transparent undersides; thus, the heart, gills, and yolk mass are visible and pigmented. The irises are mostly black but have scattered iridophores that shine golden. Iridophores on the sclera have a silvery blue tone, and a thin silver ring surrounds the pupil (Etter et al. 2021).

Variation:

Larvae exhibit ontogenetic differences. In earlier developmental stages, tadpoles appear embryonic. The eyes and nose are small and undifferentiated, even possibly non-functional. Unlike later developmental stages, earlier stages have larger abdomens compared to the trunk, resulting in a pear-shaped body. Thus, the trunk is the widest part of the body. The posteroventral skin flap is also just starting to form at earlier stages. Lastly, the limbs appear to develop faster than expected when compared to rates of somatic differentiation (Etter et al. 2021).

Life History:

At the time of the species description, P. nepenthophilus tadpoles had only been found in the phytotelmata (fluid-filled cavities) of Nepenthes mollis. Thus, they are assumed to be Nepenthes pitcher specialists, although whether the association is obligatory is unclear. Usually the larvae are inactive, resting among debris at the bottom of the pitcher. They have also been observed attached to the pitcher’s walls, suggesting that the tadpole has some sort of adhesive mechanism. The relationship between P. nepenthophilus and N. mollis is thought to be mutualistic: P. nepenthophilus tadpoles may provide nitrogen from feces, skin shedding, and egg capsules, and N. mollis provides shelter from predators and desiccation. However, the extent of benefits for N. mollis still needs to be investigated (Etter et al. 2021).

Tadpoles in different life stages are sometimes found in a single pitcher. This suggests that successive spawning may occur in the same pitcher, though it is unclear whether all the larvae are from a single female or multiple females (Etter et al. 2021).

Due to the presence of the yolk sac, reduced mouthparts, and large egg sizes, it is thought that P. nepenthophilus larvae are endotrophic, feeding only from their yolk (Etter et al. 2021).

Although the function of the posteroventral flap is still unknown, the flap is thought to either aid in gas exchange or help the larvae attach to the walls of the pitcher plant (Etter et al. 2021).

Trends and Threats
At the time of the species description, P. nepenthophilus has not been evaluated for any conservation concerns by the IUCN. Etter et al. (2021) also do not list any potential conservation concerns or give any recommended listings for this species.

Relation to Humans
Etter et al. (2021) do not give any substantial interactions humans have with this species and further research was unable to recover any.

Comments

PHYLOGENETIC RELATIONSHIPS:

The description of Philautus nepenthophilus is based on morphological, bioacoustic, and molecular information. In their description of the species, Etter et al. (2021) presented a new phylogeny of Bornean Philautus based on the mitochondrial genes CytB and 12S-Val-16S and the nuclear genes POMC, BDNF, and NTF3. These sequences were analyzed using both maximum likelihood and Bayesian inference methods. Both methods always recovered P. nepenthophilus as a distinct evolutionary lineage sister to P. macroscelis. However, the analyses could not clearly resolve the relationship between other Philautus from Sabah and Sarawak, as the clades composed of P. macroscelis + P. nepenthophilus, P. hosii + P. ingeri, P. tectus, and a clade including all other Philautus species resulted in a polytomy (Etter et al. 2021).

References
Etter, L., Haas, A., Lee, C. C., Min, P. Y., Das, I., and Hertwig, S. T. (2021). Out of the trap: A new phytothelm-breeding species of Philautus and an updated phylogeny of Bornean bush frogs (Anura: Rhacophoridae). Journal of Zoological Systematics and Evolutionary Research, 59(5), 1064–1096. [link]

Hertwig, S. T., Min, P. Y., Haas, A., and Das, I. (2014). Dressed in black. A new Ansonia Stoliczka, 1870 (Lissamphibia: Anura: Bufonidae) from Gunung Murud, Sarawak, East Malaysia (Borneo). Zootaxa, 3814(3), 419. [link]

Miyamoto, K., Wagai, R., Aiba, S., and Nilus, R. (2016). Variation in the aboveground stand structure and fine-root biomass of Bornean heath (kerangas) forests in relation to altitude and soil nitrogen availability. Trees, 30(2), 385–394. [link]

Species Account Citation: AmphibiaWeb 2024 Philautus nepenthophilus: Nepenthes Bush Frog <https://amphibiaweb.org/species/9427> University of California, Berkeley, CA, USA. Accessed May 9, 2025.

Citation: AmphibiaWeb. 2025. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 9 May 2025.

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