Description
Platymantis spelaeus is a small frog, though relatively large for the genus Platymantis. Adult females measure 52.8-60.5 mm in SVL, with males reaching 41.5-46.9 mm (Brown and Alcala 1982). The snout is broadly rounded, with the upper jaw protruding (Brown and Alcala 1982). The canthus rostralis is rounded and the lores are concave and moderately oblique (Brown and Alcala 1982). The tympanum is relatively large (Brown and Alcala 1982). Fingers are slender and lack webbing, whereas the toes have slight webbing at the base (Brown and Alcala 1982). The first finger is slightly longer than the second when adpressed (Brown and Alcala 1982). Finger discs are only slightly dilated and are about the same diameter as the toe discs; both sets of discs have a circummarginal groove but lack a transverse ventral groove (Brown and Alcala 1982). Fingers have distinct rounded subarticular tubercles and a prominent palmar tubercle at the base, plus three large metacarpal tubercles (Brown and Alcala 1982). Toes have prominent subarticular tubercles which are somewhat pointed; there is an elongate outer metatarsal tubercle and a rounded inner one, and solar tubercles are absent (Brown and Alcala 1982). Hind limbs are relatively long (Brown and Alcala 1982). The skin is shagreened, with small dorsal dermal tubercles, and lacks dorsal ridges (Brown and Alcala 1982). The rictal tubercle cluster is small and frequently consists of a single tubercle (Siler et al. 2007).

In life the dorsal coloration is olive-green to brown, with darker mottling. The thighs have dark bars on the upper surfaces and have orange or lavender inner surfaces. The ventrum is creamy and sometimes has brown flecking (Brown and Alcala 1982).

This species is a member of the Platymantis dorsalis group, which is characterized by small, blunt digital discs, narrow subtending part of the digits, strongly protruding subarticular tubercles which are usually pointed, and non-T-shaped terminal phalanges (Alcala and Brown 1998).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Philippines

View distribution map in BerkeleyMapper.

The Negros Cave Frog is a terrestrial frog found in limestone caves and limestone rock crevices, in forested areas, as well as limestone forests with open canopy, including secondary forests and tree plantation. The caves in which these frogs were first discovered are located along the coast in Southeastern Negros, Philippines, at an elevation of 20-400 m above sea level (Brown and Alcala 1982).

Life History, Abundance, Activity, and Special Behaviors

Platymantis spelaeus is unusual in that it is a cave-dwelling frog, (though it does not appear to be exclusively found in caves, as it also occurs in limestone rock crevices, within forested areas; Alcala et al. 2004). The initial specimens were collected near the entrances of moist limestone caves, in crevices within the walls or the floor (Brown and Alcala 1982). It is nocturnal (Alcala and Brown 1998).

Platymantis spelaeus males call in large choruses, particularly on rainy evenings in the hours immediately following sunset. These frogs call from small caves, both inside and at the cave mouths, as well as farther away from caves. Frogs calling at locations away from caves were observed on limestone hillsides, disturbed scrubby vegetation, and limestone boulders at the edges of fields. The call is a complex tonal whistle with two syllables that sounds bird-like. The syllables consist of a higher frequency first note and lower frequency second note of roughly equal duration. Initially there are 2-4 single calls ("pee-coh"), progressing to 2-5 paired two-note calls with a brief pause in between ("pee-coh, pee-coh...pee-coh, pee-coh"). The first note begins at 2.2-2.4 kHz, rises to 2.4-2.8 kHz in mid-call, then falls away to 1.9-2.1 kHz. The second note is more complex, beginning with an initial rapidly pulsed vibrational element that converts to a pure tone of about 1.7-1.89 kHz, rising to 2.1 kHz, and finally falling to 1.9 kHz. For paired calls, the harmonic structure is more complex for the second call than for the first, or for unpaired (single) calls, with as many as 5-6 harmonic multiples of the fundamental on the first note of the second call (vs. 2-3 multiples otherwise) (Brown et al. 2002).

This species also probably has direct development, like all other species of Philippine Platymantis where the reproductive mode is known, but unlike most frogs. The eggs are fairly large (2.5-3.0 mm in diameter) and unpigmented. Embryos develop directly into froglets, bypassing the tadpole developmental stages (Alcala and Brown 1998).

Trends and Threats
This frog was thought to be critically endangered (Alcala and Alcala 2000), and perhaps extinct in the caves in which it was first discovered (Alcala and Brown, 1998), but has since been detected in surveys (Alcala et al. 2004). It has declined in population but appears to be present at moderate population densities within the fragments of suitable limestone forest habitat that still exist in southwestern Negros, both primary forest fragments and reforested areas (Alcala et al. 2004). Surveys detected Platymantis spelaeus in eight limestone forest fragments, with a density calculated at 738-800 individuals per hectare (Alcala et al. 2004). An unpublished survey conducted in 2000, based on visual counts of adults and subadults in the Basay area of Negros Oriental estimated the density of Platymantis spelaeus in that area to be 1800 individuals per hectare (Dolino 2001, unpublished, cited in Alcala et al. 2004).

However, because the species is found only in limestone areas not greater than 600 km2 in area, Alcala et al. (2004) have recommended that Platymantis spelaeus should retain its ‘endangered’ status. Habitat loss due to deforestation is a particular threat, and disease from newly introduced species may also have been a factor in the population decline (Turner et. al. 2003).

Possible reasons for amphibian decline

General habitat alteration and loss
Disease

Comments
The related species Platymantis insulatus has also been reported to be cave-dwelling (Brown and Alcala 1970).

References

Alcala, A. C. and Brown, W. C. (1998). Philippine Amphibians: Illustrated Field Guide. Bookmark, Inc., Philippines.

Alcala, A. C., and Alcala, E. L. (2000). ''The Negros Cave Frog is critically endangered.'' Froglog 2000, 39, 1.

Alcala, E. L., Alcala, A. C., and Dolino, C. N. (2005). ''Amphibians and reptiles in tropical rainforest fragments on Negros Island, the Philippines.'' Environmental Conservation, 31, 254-261.

Brown, R. M., Dolino, C. N., Alcala, E., Diesmos, A. C., and Alcala, A. C. (2002). ''The advertisement calls of two endangered species of endemic Philippine frogs: Platymantis spelaeus and Platymantis insulatus (Anura: Ranidae).'' Silliman Journal, 43(1), 91-109.

Brown, W. C. and Alcala, A. C. (1970). ''A new species of the genus Platymantis (Ranidae) with a list of amphibians known from South Gigante Island, Philippines.'' Occasional Papers of the California Academy of Sciences, 84, 1-8.

Brown, W. C. and Alcala, A. C. (1982). ''A new cave Platymantis (Amphibia: Ranidae) from the Philippine Islands.'' Proceedings of the Biological Society of Washington, 95, 386-391.

Turner, C. S., Tamblyn, A., Dray, R., Maunder, L., and Raines, P. S. (2003). The Biodiversity of the Upper Imbang-Caliban Watershed, North Negros Forest Reserve, Negros Occidental, Philippines. Coral Cay Conservation, London.

Species Account Citation: AmphibiaWeb 2008 Platymantis spelaeus: Negros Cave Frog <https://amphibiaweb.org/species/4918> University of California, Berkeley, CA, USA. Accessed Jan 3, 2025.

Citation: AmphibiaWeb. 2025. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 3 Jan 2025.

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