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Staurois tuberilinguis (common names: Borneo splash frog, green-spotted rock frog) is a semi-aquatic amphibian of the true frog family (Ranidae). It is also commonly associated with its very close relative Staurois Parvus (common name: Borneo rock frog). In fact, many do not consider the two species to be taxonomically separate. This species is commonly found within the tropical rainforests of on Borneo (Malaysia) next to fast-flowing rivers and streams. Due to the frog’s noisy choice of habitat, Staurois Parvus are well-known for their multi-modal system of communication that combines acoustic calls with visual display signals.

Tadpole Morphology
Staurois parvus tadpoles possess a strongly depressed body with small subcutaneous eyes, tiny external nares, a vermiform appearance with a long tail and reduced fins, and a nearly pigmentless skin. Compared to Staurois tuberilinguis, the two tadpoles are nearly indistinguishable minus the fact that Staurois parvus contains various white isolated acini of its body and tail.  

Adult Morphology
Its snout-vent length is 27 - 31 mm in males and 33 - 38 mm in females. It has a markedly slender head with a pointed snout and a rather short fourth finger, distinguishing it from its relatives. Its vomer lacks teeth, and it has a lingual papilla. The eggs are unpigmented.

Ontogenetic Development
When Staurois parvus first metamorphosize from being a tadpole, they possess white and bluish coloration on their feet to assist with visual signaling. As they age, however, from juvenile to adult, that coloration increases in brightness to enhance their visual conspicuousness. Meta-analytical studies have shown that this ontogenetic chance in coloration occurs synchronously with sexual development and maturity in Staurois parvus. In terms of bodily changes, Staurois parvus juveniles begin as bright green, which serve as a form of camouflage as Staurois parvus are known to dwell nearly mossy rocks next to rivers and streams in rainforest environments.

Close Relatives
Staurois parvus are most closely related to Staurois tuberilinguis. In fact, aside from one or two morphological differences, the two species are virtually indistinguishable from each other. Genetic analysis tests have also shown that these two species are nearly the same genetic sequence. Therefore, there has been much discussion as to whether these two species are in fact taxonomically distinct. Other close relatives of Staurois parvus include Staurois guttatus and Staurois latopalmatus – both members of the Staurois family.

Habitat and Distribution
It is found in northern Borneo in Sabah and Sarawak (Malaysia), Brunei, and northeastern Kalimantan (Indonesia) to 2000 m asl.

A smaller relative, only known from the Crocker Range in Sabah (Malaysia), was described as Staurois parvus. Later, it was considered a junior synonym of S. tuberilinguis, but more recently it was confirmed to be distinct according to morphological and DNA sequence data.

This frog is diurnal and crepuscular and it is commonly found along the banks of small, rocky streams with clear water in primary rainforests. They can often be seen perched on rocks or other vegetation near water, usually around the rapids. They breed in streams and the males vocalize during the day. Like other members of Staurois, they use visual signalling to attract a mate.

Mating
Around 1-2 years after being born, the Bornean rock frog attains sexual maturity and will release a mating call. Afterwards, males settle near the side of the riverbeds and await females as they arrive. During this period of pre-female waiting, the riverside is significantly male dominant, and there is a large amount of intrasexual competition taking place. Males will puff out their vocal sac and adjust their posture to exhibit their physique and coloration in order to either intimate or deter the other males in that are looking to occupy their territory. The shallow portions of the river, or the areas where there is denser foliage – which are more suitable for egg laying, are predominantly occupied by the larger males.

Once the females arrive, Staurois parvus will release an advertisement call, to signal to the females their presence. Once the female is aware of the male’s presence, the male will exhibit some form of visual signal to communicate its physical prowess and fitness, usually in the form of either foot flagging or foot flashing. More mature Staurois parvus males will have brighter body coloration, and therefore color intensity serves as a proxy for age and development for the females. Additionally, because the act of foot flagging and flashing is quite physically demanding, the elaborateness and complexity of the foot display is indicative of the physical ability of the Staurois parvus male. Once the courtship ends, the male and female Staurois parvus will migrate to the water and engage in an amplexus position and the female will lay her eggs. Because Staurois parvus lay their eggs in fast-flowing waters, to prevent the eggs from getting swept away, the female will lay her eggs either under heavy leaf litter, between rocks, or within the side pools of streams where the water is not as violent.

Communication
Staurois parvus commonly live in noisy tropical rainforests near fast flowing streams, which makes the usual acoustic means of communication less reliable. Therefore, Staurois parvus have an array of strategies to be able to effectively communicate in the presence of high background noise. One such strategy employed by Staurois parvus involves intensity amplification of their acoustic calls. If the background noise is too loud, then the Bornean Rock Frog is able to elevate the volume of its advertisement calls, up to 8 dB, in order to have its acoustic calls be heard by the receiver. On the other hand, Staurois parvus is able to modulate the pitch of its calls slightly away from its dominant calling frequency of 5578 Hz. It is hypothesized to do so in order to avoid jamming interference from the acoustic calls of conspecifics and heterospecifics. Additionally, Staurois parvus delivers a unique advertisement call that differentiates its call from that of similar relatives such as Staurois guttatus. Depending on the number of receivers and the background noise levels, Staurois parvus have been observed to increase the number of notes and the length of their calls. This presumedly is done to give the intended receiver more opportunity to recognize and identify the call.

In extremely loud environments where vocal communication is not feasible, Staurois parvus are able to rely on visual modes of communication. Staurois parvus exhibit a large repertoire of visual communication displays, most commonly foot flagging and foot flashing. To a lesser extent, other forms of visual communication by Staurois parvus include arm waving, upright posture, crotched posture, and an open-mouth display. Foot flagging is the act of raising either of the two hind limbs and rotating it outwards and backwards in an arc. During this behavior, which lasts on average 1.5 seconds, the frog’s webbed toes are spread, allowing for the frog’s conspicuous white webbing to be clearly observed by the receiver. Foot flashing is similar to foot flagging, except the hind limbs are not rotated; rather, the hind limb is stretched outwards and retracted immediately. Foot flashes are very fast, lasting about 0.83 seconds, and only occur following an acoustic call. In noisy environments like the rainforest, the purpose of the advertisement call is to direct the attention of receiver towards the signaler. Once the Staurois parvus has its recipient’s attention, then it will follow-up with its visual display – typically a foot flag or flash. The less common visual displays – upright posture, crouching, and arm waving – are usually only displayed by Staurois parvus in close male-male encounters. These visual displays are typically done to communicate the male’s physical ability.

Overall, Staurois parvus possess a unique system of multi-modal communication that helps them to adapt and communicate in dynamic and noisy environments. This is especially the case in habitats like the tropical rainforest where rainfall is variable, and light can be scarce due to the overhead canopy. Therefore, when rainfall becomes violent and the background noise intensifies, or in low light conditions, visual modes of communication become favored. On the other hand, if there is low background noise and light conditions are appropriate, then acoustic means of communication become more advantageous. Therefore, Staurois parvus have developed an adaptive multi-modal communication system to overcome the dynamic conditions of their environment.

Diet
As a tadpole, Staurois parvus are able to only decomposed plants and algae. Once they metamorphosize, their diet expands to include insects. However, because adult Staurois parvus have a small body size, their diet is mostly limited to small insects such as flies, moths, and dragonflies. Overall, Staurois parvus are considered an opportunistic feeder, and will feed on anything that enters its domain of capture. Therefore, its diet as an adult mostly depends on the relative abundance of whatever prey during that season of the year.

Impact of Deforestation
Deforestation by logging of forests and subsequent sedimentation and alteration of stream conditions are the primary threats to Staurois parvus populations. Although Staurois parvus is currently categorized as a species of least concern on the IUIC Red List, its population numbers have been steadily declining in recent years due to increased loss of habitat and habitat pollution. This species is found in Mt. Kinabalu and Gunung Mulu National Parks which are well protected. However, the mountains in Kalimantan need urgent and increased protection.