Bornean Smaller Gliding Frog

Rhacophorus borneensis is a frog with a total snout vent length (SVL) of approximately 50.9 mm and a dorsoventrally compressed body. The head has a width of 37.5% SVL and length of 38.9% SVL; the eyes are only 14.1% SVL with horizontal pupils and oblique supratympanic fold extending from eye above tympanum to slightly above arm intersection. The snout is 18.1% SVL and when looking at it in profile, it is rounded dorsally and sloping anteroventrally. The snout has a pointed tip and projects slightly over the lower jaw. Located near the tip of the snout are the slightly protuberant nostrils; internarial distance is approximately 12% SVL. The lore is slightly oblique and concave. Regarding the canthus, it is blunt and distinct. The tympanum has a subcircular shape and length of approximately 7.7% SVL. The distance away from the eyes is an estimated two-thirds eye diameter. Forelimbs are 42.2% SVL and seem moderately long adjacent to the body. Relative finger lengths are ordered as 1 < 2 < 4 < 3; the first finger being about 5 mm. Located at each finger end are elongated large disks with circummarginal and transverse ventral grooves. In addition, there is significantly broad webbing present on all fingers. R. borneensis has indistinct flat inner palmar tubercles. An additional oval-shaped rudimentary digit on the preaxial side of the thumb is prominent. Nuptial pads are present on the outer margins of the extra digit and finger 1. The hind limbs are unusually long at about 79 mm, which is about twice the size of the forelimb. A significant physical trait R. borneensis posses is a hind limb with narrow fringes of skin along the inner edge of the first toe and outer edge of fifth. The thigh is about half the length of the snout vent length and slightly shorter than the tibia. When limbs are in a right-angle position to the body, the heels tend to slightly overlap. Feet are approximately 24 mm, toe lengths have the relative order of 1< 2 < 3 < 5 < 4, and expanded disks are present. Specifically, disk diameter of toe 4 is 2 mm and all toes are webbed to disks. There are no supernumerary metacarpal tubercles or outer metatarsal tubercle. The dorsum, underside of chin, and the chest are smooth while the flanks are wrinkled and the abdomen and thigh are coarsely granular. Rhacophorus borneensis lacks a dorsolateral fold (Matsui et al. 2013).Rhacophorus borneensis can be distinguished from other species in the Rhacophorus reinwardtii group by a variety of morphological traits. For example, R. borneensis has a much smaller body size when compared to R. nigropalmatus which has a snout vent length of 78.7 - 88.6 mm in males and 89.0 - 100.3 mm in females. R. borneensis has fingers fully webbed to discs while R. nigropalmatus has incomplete webbing between fingers 1 and 2. Coloration also drastically differs from R. nigropalmatus which has a randomly black spotted green dorsum (as opposed to uniformly green), white venter with yellow mottling (instead of a yellowish orange venter with black mottling), uniformly yellow posterior thigh surface (not the black, studded with light blue spots in females or yellowish orange in males), and lacks a black axillary patch (which is present in R. borneensis). While size and the presence of a double-lobed supracloacal dermal ridge makes Rhacophorus borneensis similar to R. reinwardtii, they differ in coloration. R. reinwardtii has a dark spotted back and yellowish orange thigh posterior surfaces rather than a green back and black thigh like in R. borneensis. Rhacophorus norhayatii has a similar male body size but different female body size, with R. norhayatii being larger (SVL 75.7-83 mm vs 62 mm in R. borneensis). R. norhayatii also differs in coloration: white venter with black marbling and blue mottling; both male and females have sky-blue studded black thighs. Rhacophorus kio has a larger body size, has a bright yellow venter, solid yellowish orange posterior thigh surface, yellow sclera, and a lot of bright yellowish orange webbing, all of which differentiate it from R. borneensis. Lastly, R. borneensis is smaller than R. helenae which has a snout vent length of 72.3 - 85.5 mm in males and 89.4 - 90.7mm in females. R. helenae also differs in coloration: it has a white venter that is bluish green with pale yellow marbling, and green or yellow webbing (Matsui et al. 2013).In life, Rhacophorus borneensis has an evenly covered green back. Lips are white with no significant pattern present. The inside of the arm through the axilla to anterior half of the flank is dark black with small yellow and blue spots. The posterior flank is yellowish orange with a few miniature black spots. Thigh coloration consists of yellowish and orange anterior and posterior surfaces. White lining present on dermal appendages on arm and leg including tibiotarsal projection and supracloacal dermal ridge; yellowish orange on the surfaces of the chest, belly, upper arms, thigh, tibia, and tarsus; chin covered with small black spots. The webbing between fingers 2 and 4 is black with fine blue streaks while the webbing between fingers 1 and 2 is yellowish orange with black spots; fingers 1 and 2 and all discs are yellowish orange. Toe webbing surface is also black with blue streaks; pigmentation of the web covering almost everything except for the base and distal edges of the toes, the remaining area is yellowish orange. Under bright conditions, the eyes show reticulation and are pale yellowish silver with thin sections of coppery brown; in the dark, the eye has a dark red iris with enlarged reticulation, black periphery, and white sclera. In preservative, all the green coloration eventually fades to violet, yellow orange fades to white, and the black pigmentation remains unchanged (Matsui et al. 2013).The female is larger than the male in all physical aspects except for the head (34.7% of the snout vent length in females, versus 38.9% snout vent length in the male), snout (15.2% SVL in females versus 18.1% SVL in males), and eye (12.6% SVL in females versus 14.1% SVL in males). Because of small sample size, these differences in measurements do not necessarily imply that this species is dimorphic. In coloration, males and females have nearly identical color uniformity with the exception of the ventral spots, thighs, tibia, and toe webbing markings. For ventral spots, the female has more refined ventral spotting than males. In males the thighs are yellowish orange while in females the thighs are black and studded with sky blue spots. In males the marginal toe webbing and the bottom of the tibia are yellowish orange unlike in females, which have more refined black markings on webbing and posses a black tibia underside. Lastly, males have slightly looser skin in the gular area, which is not present on females (Matsui et al. 2013).Phylogenetic Relationships: Rhacophorus borneensis has a small genetic difference of about 0 - 0.2% in its 16S rRNA sequence with R. reinwardtii sampled from Malaysia and another narrow genetic difference of 0.2 - 0.8% with R. reinwardtii sampled from Sarawak, suggesting that these were conspecific with the new species (Matsui et al. 2013). Etymology: The species is named after the island where it was discovered, Borneo (Matsui et al. 2013).

Rhacophorus borneensis can be found in a series of locations: Camel Trophy of the Maliau Basin Conservation Area, Sandakan Division, State of Sabah, Malaysian Borneo; Batang Ai, State of Sarawak, Malaysian Borneo (Matsui et al. 2013).

R. borneensis is a very conspicuous species with a large body, bright coloration, and broad webbing. However, because it lives on tall trees most of the time, it cannot easily be observed or sampled, so information on this species is limited. Some observations taken in Camel Trophy detected individuals on tree branches a little more than 1 m off the ground that extended above the surface of a shallow pool. During this time, early March, air temperature was about 24°C and no calling males, tadpoles or eggs were found. Surprisingly, R. borneensis was found interacting with other species that included Kurixalus appendiculatus, Polypedates macrotis, Chiromantis, and Microhyla petrigena (Matsui et al. 2013).

Currently threatened by being overharvested for medicine, food, pet trade, and by the general habitat loss and alteration caused by the logging of primary forests (Matsui et al. 2013).

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Rhacophorus borneensis is a species of frog in the family Rhacophoridae. This recently (2013) described species is endemic to Malaysian Borneo where it is known from its type locality in the Maliau Basin Conservation Area, Sandakan Division, Sabah as well as from the Batang Ai National Park, Sarawak. Prior to its description, it was included in Rhacophorus reinwardtii. It is said to be "one of the prettiest frogs of Borneo". Common name Borneo flying frog has been coined for it.

class=notpageimage| Rhacophorus borneensis is only known from two locations in Malaysian Borneo.