The species epithet, “guttatus” means “shaped like or resembling drops, spotted” in Latin.

Frogs of Borneo.

Description
Staurois guttatus, the Black-spotted Rock Frog, is a relatively small frog with a slender body and long snout that appears pointed and protruding from a lateral view point (Haas et al. 2018). These frogs are sexually dimorphic in terms of size, with females being much larger than males. On average, males have a snout vent length of 34.9 - 37.7 mm while females have an average snout vent length of 38.0 - 54.7 mm (Grafe and Wagner 2007). Small tympani are visible posterior to the eye. Its skin has a warty texture, which is heaviest on the dorsolateral surface, but can be observed to a lesser extent on the legs and undersides as well. This frog has long digits, of which the tips fan dramatically outwards; there is webbing between the toes (Haas et al. 2018).

Another member of the same genus, S. tuberilinguis, looks extremely similar. However, it can be differentiated by its underside, which is a mottled light blue and its dorsal coloration, which is a lighter green than S. guttatus (Hass et al. 2018).

In life, the dorsal region of S. guttatus ranges from a muddled tan to olive brown and is stippled with various-sized dark spots. Its flanks range from pale green to light yellow with extremely small white spots dotting them. It has a continuous dark band that separates its dorsal and flank coloration. The webbing between its toes is most commonly a bright white that contrasts dramatically with its body coloration, but may have a blue tinge in some members of the species. Its underside is mostly yellow white, but not nearly as vibrant as the inner-toe webbing. Lining the underside of each eye is a blue crescent. The iris of the eye has a copper-colored inner ring and dark outer ring, except for a small bit of silver coloration located at the lower portion of the eye (Haas et al. 2018).

There is coloration variation based on development. Interdigital webbing in juveniles is more transparent than that of the adult frogs (Preininger et al. 2012, Stangel et al. 2015).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Malaysia

Malaysian region distribution from AmphibiaWeb's database: Sabah, Sarawak

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (3 records).

Staurois guttatus can be found throughout the island of Borneo, within the borders of all three nations on the island, Brunei Darussalam, Indonesia (Kalimantan), and Malaysia (Sarawak, Sabah) in inland terrestrial wetland forests. They are commonly found along medium-sized streams, side streams, and in the splash zones of waterfalls at elevations between 150 – 1,000 m asl (Haas et al. 2018, IUCN 2018).

Life History, Abundance, Activity, and Special Behaviors
Frogs of this genus dwell exclusively in and near fast flowing, clear rainforest streams. They perch most commonly on low hanging vegetation less than 150 cm from the ground along stream banks or on vegetation that grows on large rocks on the banks itself (Haas et al. 2018, IUCN 2018).

Courtship and coupling of adults occurs on land, and then moves to water for spawning (Preininger et al. 2012).

The frogs engage in pectoral amplexus. In Staurois, the male flexes first, then the female, in order to bring the cloacas closer for mating. Eggs, with black ova, are deposited between the legs, which form a triangular shape (Jameson 1957, Matsui et al. 2007). In captivity, these frogs have been observed to lay their eggs between rocks. Stauroris guttatus has also been shown to dive below waterfalls while in amplexus, suggesting that they may lay their eggs in suitable underwater cavities, especially in locations where there is heavy leaf litter. Once matured, this diurnal stream-dwelling species spends its entire life very close to fast-slowing water systems (Preininger et al. 2012).

Typical of the Staurois genus, S. guttatus exhibits unique visual behaviors that are most likely an adaptation to overcoming barriers of communication associated with the loud, fast-flowing stream environments in which these frogs inhabit (Preininger et al. 2012, 2016). The most notable and well-studied of these visual behaviors is foot-flagging. This display can be observed in juveniles just days after metamorphosis and consists of extending and rotating the legs to briefly flash their white foot webbing. Unlike most anurans that display this behavior, this is not solely a male communication device as females of S. guttatus have also been observed engaging in these displays as well (Preininger et al. 2012, Stangel et al. 2015). Flagging has been experimentally linked with advertisement calls, which hypothetically serve to draw attention to the foot-flagging display itself (Grafe and Wanger 2007). However, the exact motivation of these displays is still undetermined. In captive populations, these behaviors were observed in several distinct instances: in males, flagging has been observed in conjunction with other males as females approach a calling site, directed towards hetero and conspecifics on the backs of the females during amplexus, or preceding a special call involving the unilateral inflation of the vocal air sacs. In females, this behavior has been observed when a male encroaches on or begins to call at a female’s territory. Therefore, it can be implied that this behavior plays both an antagonistic and reproductive role, but whether it is involved in mate competition or directly through mate choice is still unknown (Preininger et al. 2012, 2016).

Staurois guttatus males have also developed special usage of their vocal sacs for multimodal communication. Of particular interest is their ability to unilaterally inflate their paired vocal sacs, a behavior that is extremely rare in anurans. Observations have found that S. gutattus inflate their paired vocal sacs asymmetrically in the presence of another male. The reason for this behavior in S. guttatus is not well understood, but the presence of another male suggests that it may also be part of an agonistic display. As of 2021, unilateral vocal sac inflation has not been reported as having usage in courtship displays, but more research is needed to determine the full function of this behavior (Elia-Costa and Faivovich 2019).

Unreceptive females of the species have been recorded making calls when approached by a male less than 30 cm away, suggesting that calls also have an agonistic function. These calls are emitted with an open mouth, as S. guttatus females have no vocal sacs (Preininger et al. 2016).

Other recorded behaviors include open mouth displays and arm waving. For the open mouth display an individual takes on an upright posture before opening their mouth wide to show the full extent of white coloration on the inner portion of the mouth. Both arm waving and the open mouth displays are believed to be agonistic displays (Preininger et al. 2016).

Nicknamed the Torrent Frog, S. guttatus possesses the extraordinary ability to adhere to surfaces even in the presence of fast-flowing water at high angles. While initially believed to be a byproduct of structures on the toe pads, it has been determined that the ventral area of these frogs plays the most critical role in this adhesion ability. While the exact mechanism is still unclear to science, it is believed that they utilize friction, their small body size, and behavioral adaptations to accomplish these feats (Endlein et al. 2013).

It sometimes occur in sympatry with Staurois parvus (Matsui et al. 2007).

Larva
Tadpoles have slender, semifossorial bodies. At stage 25, their body length ranges from 5.4 mm to 9.8 mm, and their total length ranges from 15.4 mm to 30.1 mm. At stages 35 to 38, their body length increases to 10.1 mm to 10.8 mm and total length ranges from 31 mm to 34.0 mm. Stage 41 larvae were similarly sized as stages 35 to 38. The tail length is 69 - 71% of the total length, while tail depth is 18 - 21% of the tail’s length. The nostrils are positioned far forward, above the corner of the oral disk. The eyes are separated from the tip of the snout by about 25 - 36% of the body length. Larvae eyes are covered with thick skin. As they develop past stage 36, a clear “window” over their eyeball replaces this skin. The labial tooth rows formulas are 2(2)/10(1), 2(2)/9(1), and 2(2)/8(1). At their pre-metamorphic stage 41, the tips of their toes are expanded into large truncate disks, with webbing between the disks. There is no webbing between the fingers (Inger and Tan 1990).

In life, tadpole skin is lacking in pigment and nearly transparent, with pinkish bellies. In preservatives, their belly changes to a shiny silver (Inger and Tan 1990).

Tadpoles vary in the labial tooth row formulas (Inger and Tan 1990).

The tadpoles of S. guttatus develop within the hyporheic interstitial zone, a region near the bottom of streams where ground and channel water interact. Tadpoles have also been found within side pools of streams, under leaf litter (Haas et al. 2018). The protection this zone provides is what allows this frog species to develop in such fast-flowing conditions.

Trends and Threats
These frogs are considered both abundant and common in the areas in which they occur. While categorized as “Least Concern” by the IUCN Red List, their population has been observed to be in decline in recent years. Specific threats include wood and pulp plantations, logging activities, and agricultural and forestry effluents. It is apparent in S. guttatus and other stream-dwelling forest frog species, that these frogs do extremely poorly in the wake of human activity and habitat alteration (IUCN 2018). They have been successfully bred at the Vienna Zoo (Preininger et al. 2012).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Local pesticides, fertilizers, and pollutants

Comments
There is discordance between Maximum Parsimony and Bayesian Inference analyses of 16S mtDNA for this genus. The maximum parsimony results indicate that S. guttatus is sister to the clade composed of S. parvus and S. tuberilinguis, however, Bayesian inference indicate that S. guttatus is sister to S. nubilus. The sister clade in the Bayesian inference analysis is composed of S. parvus and S. tuberilinguis (Arifin et al. 2011).

Staurois guttatus was formerly synonymized with S. natator (Matsui et al. 2007).

References

Arifin U, Iskandar DT, Bickford DP, Brown RM, Meier R, Kutty SN (2011) "Phylogenetic relationships within the genus Staurois (Anura, Ranidae) based on 16S rRNA sequences." Zootaxa 2744: 39-54. [link]

Endlein, T., Barnes, W.J.P., Samuel, D.S., Crawford, N.A., Biaw, A.B., Grafe, U. (2013). "Sticking under wet conditions: the remarkable attachment abilities of the torrent frog, Staurois guttatus." PLoS ONE 8, e73810 [link]

Grafe, T.U., Wanger, T.C. (2007). "Multimodal signaling in male and female foot-flagging frogs Staurois guttatus (Ranidae): an alerting function of calling." Ethology 113, 772–781. [link]

Haas, A., Boon-Hee, K., Joseph, A., Bin Asri, M., Das, I., Hagmann, R., Schwander, L., Hertwig, S. (2018). "An updated checklist of the amphibian diversity of Maliau Basin Conservation Area, Sabah, Malaysia." Evolutionary Systematics 2, 89–114. [link]

IUCN SSC Amphibian Specialist Group. (2018). "Staurois guttatus." The IUCN Red List of Threatened Species 2018: e.T56350253A56350722. https://dx.doi.org/10.2305/IUCN.UK.2018-1.RLTS.T56350253A56350722.en. Downloaded on 01 November 2021.

Inger, R. F., Tan, F.L. (1990). "Recently discovered and newly assigned frog larvae (Ranidae and Rhacophoridae) from Borneo." Raffles Bulletin of Zoology 38(1), 3-9. [link]

Jameson, D.L. (1957). "Life history and phylogeny in the Salientians." Systematic Zoology, 6(2), 75-78. [link]

Matsui, M., Mohamed, M., Shimada, T., and Sudin, A. (2007). "Resurrection of Staurois parvus from S. tuberilinguis from Borneo (Amphibia, Ranidae)." Zoological Science. Tokyo 24(1), 101–106. [link]

Preininger, D., Handschuh, S., Boeckle, M., Sztatecsny, M., Hödl, W. (2016). "Comparison of female and male vocalisation and larynx morphology in the size dimorphic foot-flagging frog species Staurois guttatus." The Herpetological Journal 26(3), 187-197. [link]

Preininger, D., Weissenbacher, A., Wampula, T., Hödl, W. (2012). "The conservation breeding of two foot-flagging frog species from Borneo, Staurois parvus and Staurois guttatus." Amphibian & Reptile Conservation 5(3), 45-56. [link]

Stangel, J., Preininger, D., Sztatecsny, M., Hödl, W. (2015). "Ontogenetic change of signal brightness in the foot-flagging frog species Staurois parvus and Staurois guttatus." Herpetologica 71, 1–7. [link]

Species Account Citation: AmphibiaWeb 2024 Staurois guttatus: Black-spotted Rock Frog <https://amphibiaweb.org/species/7622> University of California, Berkeley, CA, USA. Accessed Jan 15, 2025.

Citation: AmphibiaWeb. 2025. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 15 Jan 2025.

AmphibiaWeb's policy on data use.