Description
Litoria gracilis is a small and slender-bodied tree frog with minimal sexual dimorphism, having a snout-vent length range of 25.1 – 28.2 mm in 12 males and 28.6 mm in one female. Based on the holotype, the species has a moderately narrow head that is slightly wider than it is long with slightly flared lips. In the dorsal view, L. gracilis’ snout is broadly rounded with an angular tip; however, in lateral view it steeply slopes to become near truncate. Litoria gracilis has a short, slightly-rounded canthal ridge, and a slightly-concave, steeply-sloping loreal region. Its nostrils are laterally oriented and are found much closer to the tip of the snout than the eyes. Additionally, its eyes are moderately small but prominent, protruding both laterally and dorsally, with a horizontally-split pupil. The tympanum is small—being only slightly larger than one-third the diameter of its eye—and is moderately well-defined, though its dorsal edge is obscured by a short supratympanic edge (Richards et al. 2023).

Litoria gracilis has shagreened dorsal skin and its throat is finely ridged while the abdomen is coarsely granular. It has moderately long limbs that have a relatively smooth ventral surface, except for numerous low but conspicuous tubercules that extend distally from its vent to about halfway along the postero-ventral margins of its thighs. A dense cluster of tubercules surround the vent and small, low tubercles are found on each heel; additionally, a line of small, pale tubercules extends from the forearm to the base of finger IV. The inner metacarpal tubercle of L. gracilis is low and elongated while the outer metacarpal tubercle is both broad and flat. The relative finger lengths are III > IV > II > I and the fingers are substantially webbed, with finger IV’s webbing extending slightly beyond the distal edge of the subarticular tubercule at the base of the penultimate phalanx. The nuptial pad is narrow and extends 1.5 mm along the outer edge of finger I. There is a low, interrupted dermal fold that extends from the heel to nearly the disc of toe V, but is reduced to a low ridge distally. No metatarsal tubercle is present, though the inner metatarsal tubercle is well-developed. Meanwhile, the relative toe lengths are IV > III = V > II > I and the inner webbing of toes V and III nearly reaches to the base of the discs. Toe IV’s webbing extends to the distal edge to the distalmost subarticular tubercule while toe II’s webbing extends to halfway between the toe disc and the distal subarticular tubercle. Toe I’s webbing extends to the distal subarticular tubercle. The tips of both the fingers and toes have distinct marginal grooves and are expanded into terminal discs, though those on the fingers are slightly broader. All toes are prominently webbed (Richards et al. 2023).

DIAGNOSIS:

Litoria gracilis can be differentiated from most Litoria due to its slender body, small size, green and brown dorsal coloration, extensively webbed fingers, and it lacking a rostral spike. It is morphologically similar to the following twelve species: L. aplini, L. daraeinsis, L. haematogaster, L. iris, L. lisae, L. majikthise, L. naispela, L. nigropunctata, L. richardsi, L. singadanae, L. umarensis, and L. verae. Most similar species of Litoria are relatively morphologically similar, but have distinctive advertisement calls that allow differentiation from L. gracilis. Additionally, there are some morphological characteristics that can be used to differentiate L. gracilis from similar species. Litoria aplini can be differentiated from L. gracilis because of its larger size, more prominent dermal fold, and a short buzz as its advertisement call, quickly followed by 1 – 7 clicks. Additionally, L. aplini’s inner limbs are blue with dark brown mottling. Litoria gracilis’ sister species, L. daraiensis, is near morphologically indistinguishable (only slightly differing in size, with L. daraiensis being slightly smaller), but can be genetically and acoustically differentiated, as L. darainensis’ advertisement call consists of 10 – 11 pulsed, chattering notes. Meanwhile, L. haematogaster can be differentiated by its larger size, extensively webbed fingers, uniform red thighs, and having a white post-ocular bar. Litoria gracilis can be further distinguished from additional species such as L. iris through L. iris’ posterior thigh being red, blue, or yellow with often purple or white blotching and an advertisement call of up to ten notes of differing length, with long notes preceding or succeeding shorter notes; from L. lisae because of L. lisae’s predominantly green dorsum, patterns with darker green and brown spots, a white bar beneath the eye, and an advertisement call that is a single buzz or chirp, which contains evenly measured pulses; from L. majikthise because of L. majikthise’s larger size, uniform red thighs, its white post-ocular bar, violet patches on the posteroventral surfaces of the abdomen, and an advertisement call that is either a single long or an incredibly condensed, short note; and from L. naispela because of its large tympanum, covered with a predominantly transparent membrane, absent vomerine teeth, and a prominent dermal fold along the outer edge of the foot. Litoria nigropunctata can be differentiated from L. gracilis because of its slightly larger size, dermal folds that form a low dermal ridge, and an advertisement call of irregular clicks; L. richardsi and L. singadanae because of their larger, substantially transparent tympanum, with L. richardsi additionally having irregular black lines on its dorsum and extensive black, ventrolateral markings, and L. singadanae’s extensively orange posteroventral surfaces; L. umarensis because of its brown posterior surfaces of its thighs and uniform green dorsum; and L. verae because of its larger size, orange posteroventral surfaces, and transversely aligned small brown spots found on the dorsum (Richards et al. 2023).

COLORATION:

VARIATION:

Although only one female was found, it was larger than the males. Additionally, nuptial pads were found exclusively on males. The extent and density of brown pigmentation is highly variable, as some specimens exhibit limited dark-brown pigmentation while others exhibit many discrete dark-brown patches on dorsal surfaces on the back and limbs. Additionally, there is considerable variation in the number and size of green spots found on the dorsum (Richards et al. 2023).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Papua New Guinea

View distribution map in BerkeleyMapper.

Kinsi P. gets joint credit

Life History, Abundance, Activity, and Special Behaviors
Males tend to call on perches on low foliage near small, shallow streams and have additionally been found near egg clutches on leaves that overhang streams (Richards et al. 2023).

Their call is a short bleat that lasts 0.13 – 0.28 seconds and contains 2 – 5 distinctly pulsed notes, with the last internote intervote lasting longer than the rest (Richards et al. 2023).

The eggs that the females of L. gracilis lay are large and yellow. Eggs are ‘glued’ to the underside of the leaves; upon hatching, they will fall directly into water (Richards et al. 2023).

Larva
Few larvae were observed. Only late stage tadpoles in eggs found glued to the underside of the leaves (Richards et al. 2023).

Trends and Threats
The broad distribution of L. gracilis in areas where much of Papua New Guinea’s primary forest still remains has led the species authority to suggest the species as “Least Concern” for its IUCN listing (Richards et al. 2023).

Comments
Litoria gracilis is the sister species to L. daraiensis based on Maximum Likelihood phylogenetic analyses of the mitochondrial ND4 gene and its flanking tRNA (Richards et al. 2023).

OTHER INTERESTING INFORMATION:

Prior to being genetically and acoustically analyzed, L. gracilis was lumped with L. nigropunctata (Richards et al. 2023).

References
Richards, S. J., Donnellan S. C., and Oliver, P. M. (2023). Five new species of the pelodryadid genus Litoria Tschudi from the southern versant of Papua New Guinea’s Central Cordillera, with observations on the diversification of reproductive strategies in Melanesian treefrogs. Zootaxa 5263(2), 151–190. [link]

Species Account Citation: AmphibiaWeb 2025 Litoria gracilis: Slender Spotted Treefrog <https://amphibiaweb.org/species/9715> 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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