Description

Diagnosis: This is a small species of Guibemantis, until recently confused with G. bicalcaratus. It has been assigned to the subgenus Pandanusicola, based on body size, phytotelm breeding in Pandanus plants, diurnality, moderately webbed toes, connected lateral metatarsalia, presence of both outer and inner metatarsal tubercles, male femoral glands of type 2, and genetic similarities. Within the subgenus Pandanusicola, G. wattersoni can be distinguished from G. albolineatus, G. bicalcaratus, G. flavobrunneus, G. liber, and G. pulcher by having conspicuous light-colored rings just proximal to each finger or toe disc, by having unpigmented eggs, by genetic differences, and probably by having paired subgular vocal sacs (vs. a single subgular vocal sac). G. wattersoni can be distinguished from G. annulatus by lacking regular, round dark spots on the dorsum, and from G. bicalcaratus by lacking regular spots on the hindlimbs.

Description: Males average 20.7 mm SVL (range 16-23 mm), females average 23.1 mm SVL (range 17-28 mm). Head is wider than body. Snout is somewhat pointed in both dorsal and lateral view, with a rounded canthus rostralis. Nares are nearer to snout tip than to eye, and point forward. Tympanum is distinct. A dark supratympanic fold is present. Vomerine odontophores present in two prominent circular patches, just posterior to choanae. Arms are thin. Relative finger length is 3>4=2>1. Fingers have moderately enlarged and rounded discs. No finger webbing present. Subarticular tubercles on hand are single, round, and enlarged. Hindlimbs are robust. When hindlimbs are adpressed, tibiotarsal articulation reaches between the eye and snout tip. Lateral metatarsalia are connected. Inner metatarsal tubercle is oblong; outer metatarsal tubercle is round. Relative toe length is 4>3>5>2>1. Toes have moderately enlarged discs, with the width of the fourth toe disc 75% of that of the third finger disc. Toes are webbed. Skin is finely granulated on the dorsum, and coarsely granulated on the venter.

The overall body color is yellow or yellowish-brown. Often there are few or no prominent dorsal markings, but sometimes the dark line associated with the supratympanic fold continues down the dorsum as a ragged line to mid-body. In some individuals this dark ragged line on the dorsum is bordered medially with a lighter (nearly white) ragged parallel line. Very small scattered white spots are also found on the dorsum and dorsal surface of the legs of some individuals (especially recent metamorphs). Paired rostral stripes (one black and one gold) are present, as are small white rings proximal to each finger or toe disc. The supratympanic fold is darkly colored. The venter is usually an immaculate light cream but sometimes dark spotting may be found along the jawline and throat, or rarely the chest. Belly and chest are often semi-transparent. The iris is metallic gold, often with irregular dark lines associated. Sexually mature males at one locality (Sainte Luce) were significantly smaller on average than females (male range: 16-23 mm SVL; female range 17-28 mm SVL). Males have paired subgular vocal sacs and well-defined femoral glands on the ventral surface of the thighs. Sexually mature males also have white coloration on the subgular vocal sacs.

Similar species: Guibemantis wattersoni can be distinguished from G. bicalcaratus by a larger body size, larger tympanum, having two conspicuous parallel rostral lines and conspicuous light “rings” just proximal to each toe or finger disc, its advertisement call and by considerable genetic differences.

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Madagascar

View distribution map in BerkeleyMapper.

While it can be locally common, at present G. wattersoni is only known from five localities in southeastern Madagascar: Ampamakiesiny Pass, Mandena, Sainte Luce, the Agnalaro Forest near Lake Ambavasohihy and lower elevations of parcel 1 of the Réserve Naturelle Intégrale d’Andohahela.

Life History, Abundance, Activity, and Special Behaviors
Breeding is confined to the rainy season (December – March), though calling has been heard outside this span after heavy rains. Calling only occurs during the day. To the human ear, the advertisement call of G. wattersoni sounds like a simple, soft “click.” These are emitted as single notes or in a succession of twos or threes at a peak frequency of approximately 3800 Hz. The sound is very similar to the calls of the syntopic species G. annulatus, but can be distinguished by a much smaller range of frequencies spanned (mean range of 345 Hz for G. wattersoni vs. mean range of 1907 Hz for G. annulatus) and reaching the peak intensity of vocalization at a lower frequency (a out 3800 Hz in G. wattersoni vs. 4500 Hz in G. annulatus).

One reproductive event has been described (Lehtinen 2003, as M. bicalcaratus) and, as in other mantellid frogs, no true amplexus occurred. Rather, the male straddled the head of the female, where sperm was presumably released.

This species is a specialist of Pandanus ('screw pine') plants. Eggs are laid on Pandanus leaves above water-filled leaf axils (clutch size averages 45 at Sainte Luce). Eggs are unpigmented and measure 1.9 mm in diameter. Males and/or females may attend the egg clutches for up to eight days or more before hatched embryos drop into the water to continue development. Tadpoles are detritivores and the larval stage lasts from two to three months. Tadpoles of this species are competitively inferior to those of a syntopic species Guibemantis annulatus but have a shorter larval period. Recently metamorphosed juveniles average 9 mm SVL.

Mark-recapture studies have suggested that the maximum life span is less than 11 months. Populations at Sainte Luce have a highly female-biased sex ratio.

Reported predators include an unidentified heteropodid spider and the colubrid snake Ithycyphus oursi.

Trends and Threats
This species was very common at Sainte Luce from 2000-2002, occupying over 60% of surveyed plants during this period. However, very little lowland (littoral) rainforest remains in this area. Habitat destruction is the largest threat to this regional endemic.

Relation to Humans
Locals use Pandanus leaves to make baskets, etc. This can damage the host plants.

Possible reasons for amphibian decline

General habitat alteration and loss
Subtle changes to necessary specialized habitat

Comments
This species was transferred to the genus Guibemantis; older literature will often list this species under the genus Mantidactylus. It is a member of the subgenus Pandanusicola.

The specific epithet wattersoni honors William 'Bill' Watterson II for his wonderful cartoon Calvin and Hobbes.

References

Lehtinen, R. M. (2003). ''Parental care and reproduction in two species of Mantidactylus (Anura: Mantellidae).'' Journal of Herpetology, 37, 766-768.

Lehtinen, R. M., Glaw, F., and Vences, M. (2011). ''Two new plant-breeding frog species (Anura: Mantellidae, Guibemantis) from southeastern Madagascar.'' The Herpetological Journal, 21, 95-112.

Species Account Citation: AmphibiaWeb 2022 Guibemantis wattersoni: Watterson’s Tree Frog <https://amphibiaweb.org/species/7654> University of California, Berkeley, CA, USA. Accessed Nov 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Nov 2024.

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