Description
Hyperolius thomensis males have snout-vent lengths of 36 – 41 mm and female snout-vent lengths of 42 – 49 mm. The body is moderately slender and the head is wider than long. The snout is short, obtusely pointed in dorsal view, and round in profile. The lateral nostrils are closer to tip of snout than eye and visible in dorsal view. The canthus rostralis is distinct and slightly constricted behind nostrils. The lores are concave and oblique. The eye diameter less than snout length. The interorbital distance is greater than the width of the upper eyelid. The pineal body not visible. The tympanum is indistinct, round, and less than half of eye diameter. The vocal sac is median and a small, rounded gular gland occupies less than half of gular area. There is no ulnar tubercle. The metacarpal tubercle is small and ovoid. The thenar tubercle well developed. The relative finger lengths are I < II < IV < III and the finger webbing formula is I 1 – 1 II ½ – 1 ½ II 1 – ½ IV. The subarticular tubercles on Fingers I – IV are round and the distal tubercle on Finger IV bifid. The tips of all four fingers are expanded into oval shaped discs with circummarginal grooves. The width of the disc on Finger III is ~1.8 times width of phalanx. Nuptial pads are absent. The outer metatarsal tubercle is round while the inner metatarsal tubercle is distinct, ovoid. The plantar surfaces are smooth. The relative toe lengths are I < II < III < V < IV and the toe webbing formula is I 1⁄2 – 1 II 0 – 1 III 0 – 1 IV 1 – 0 V. There are well-developed, round subarticular tubercles on toes. The tips of all five toes are expanded with the width of Toe IV disc being ~1.7 times width of phalanx. The skin on dorsum finely is granular, the skin on dorsal side of limbs granular, and the skin on ventral surface coarsely granular, while the skin is smooth on chest and ventral sides of limbs. The dorsolateral fold absent, but fine dorsal asperities are present in males (Bell 2016).

Multilocus molecular data indicate that H. thomensis is in the genus Hyperolius and is part of the H. cinnamomeoventris species complex, which includes six described species: H. cinnamomeoventris, H. olivaceus, and H. veithi from continental Africa, H. molleri and H. thomensis endemic to São Tomé Island, and H. drewesi endemic to Príncipe Island in the Gulf of Guinea archipelago (Schick et al. 2010; Bell et al. 2015 J. Bio., Bell 2016, Bell et al. 2017). Hyperolius thomensis is sexually monochromatic and color polymorphic (males and females vary in color from uniform brown, to green, to blue-green) and differs in color from H. cinnamomeoventris and H. olivaceus, which are sexually dichromatic (females are green and males are tan with bright yellow dorsolateral lines), and from H. veithi, which is sexually monochromatic (both sexes are tan with bright yellow dorsolateral lines). Hyperolius thomensis differs from H. molleri and H. drewesi in male body size (the snout-vent lengths of H. molleri is 23 – 32 mm, H. drewesi is 25 –31 mm, and H. thomensis is 36 – 41 mm), in the distal portion of the terminal phalanx (H. molleri and H. drewesi are disc shaped while H. thomensis is oval/wider in horizontal plane), and in ventral coloration (H. molleri is red/orange/white, H. drewesi is white, H. thomensis is marbled black/orange; Bell 2016).

In life, the dorsum, dorsal surface of forelimb and hindlimb are brown, green, or blue-green. The dorsal asperities are black. The dorsal surface of thigh is marbled black and orange with a thin green medial band that has a thick black contour extending from dorsum to lower limb. The side of head brown, green, or blue-green. The dorsal surface of fingers and toes are orange. The ventral surfaces are orange with large black blotches. The chest is white with an orange wash and black blotches. The iris is gold (Bell 2016).

In preservative, the dorsum, side of head, and dorsal surface of forelimb and hindlimb are brownish grey. The dorsal asperities are dark. The dorsal surface of the thigh is cream with black blotches and a thin brown medial band that has a thick black contour extending from dorsum to lower limb. The ventral surfaces are cream with black blotches (Bell 2016).

There is some sexual dimorphism. Males have a round gular gland that occupies less than half of gular area, vocal sac, and dorsal asperities. Females are larger than males (Bell 2016).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Sao Tome and Principe

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (1 records).

Hyperolius thomensis occurs in primary and closed-canopy forest on São Tomé Island at elevational ranges 250 – 1350 m. Sites at the boundary of primary and second forest contain a high proportion of hybrid H. molleri – H. thomensis frogs (Bell et al. 2015 Evolution).

Life History, Abundance, Activity, and Special Behaviors
Hyperolius thomensis can be found during visual surveys at night approximately 1 to > 5 m above the ground on leaves and thin branches near breeding sites (Gilbert and Bell 2018).

The dominant frequency range of the advertisement call for H. thomensis is 2338 – 2654 Hz with an average of 2513 Hz (Gilbert and Bell 2018).

Hyperolius thomensis breed in phytotelmata, including decaying logs and bamboo (Drewes and Stoelting, 2004). Females deposit eggs on the surface of leaves overhanging water or directly on the surface of the phytotelmata structure.

Trends and Threats
Hyperolius thomensis has an IUCN Red List status of “Endangered” because it has an Extent of Occurrence is less than 5,000 km² and that range is severely fragmented with quality and extent continuing to decline (Drewes and Schiøtz 2004).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Habitat fragmentation

Comments
The species authority is: Bocage, J. V. B. du. (1886). “Reptiles et bataciens nouveaux de l’Ie de St. Thomé.” Jornal de Sciências, Mathemáticas, Physicas e Naturaes. Lisboa 11: 71–75.

Analysis of 16S and cytb mtDNA indicate that H. thomensis sister to the clade formed by H. drewesi and H. molleri. Together they from a clade of Hyperolius island endemics. The next most closely related species is Hyperolius olivaceus (Bell et al. 2017).

Hyperolius thomensis is an island giant; it is one of the largest member of the genus Hyperolius (Robert C. Drewes per. comm).

References

Bell R.C., Drewes, R.C., Zamudio K.R. (2015). ''Reed frog diversification in the Gulf of Guinea: overseas dispersal, the progression rule, and in situ speciation.'' Evolution , 69(4), 904–915. [link]

Bell RC, Drewes, RC, Channing A, Gvozdik V, Kielgast J, Lötters S, Stuart BL, Zamudio KR (2015). ''Overseas dispersal of Hyperolius reed frogs from Central Africa to the oceanic islands of Sao Tome and Principe.'' Journal of Biogeography, 42(1), 65-75. [link]

Bell RC, Parra JL, Badjedjea G, Barej MF, Blackburn DC, Burger M, Channing A, Dehling JM, Greenbaum E, Gvozdík V, Kielgast J, Kusamba C, Lötters S, McLaughlin PJ, Nagy ZT, Rödel M-O, Portik DM, Stuart BL, VanDerWal J, Zassi-Boulu, A-G, Zamudio KR (2017). ''Idiosyncratic responses to climate-driven forest fragmentation and marine incursions in reed frogs from Central Africa and the Gulf of Guinea Islands.'' Molecular Ecology, 26(19), 5223-5244. [link]

Bell, R.C. (2016). ''A new species of Hyperolius (Amphibia: Hyperoliidae) from Príncipe Island, Democratic Republic of São Tomé and Príncipe.'' Herpetologica , 72(4), 343-351. [link]

Drewes, R. and Wilkinson, J. (2004). ''The California Academy of Sciences Gulf of Guinea expedition I: The taxonomic status of the genus Nesionixalus with comments on the genus Hyperolius.'' Proceedings of the California Academy of Sciences, 55(20), 395-407.

Drewes, R., Schiøtz, A. (2004). ''Hyperolius thomensis''. The IUCN Red List of Threatened Species 2004: e.T56289A11442549. https://dx.doi.org/10.2305/IUCN.UK.2004.RLTS.T56289A11442549.en. Downloaded on 23 August 2020.

Drewes, R., and Stoelting, R. E. (2004). ''The California Academy of Sciences Gulf of Guinea expedition (2001) II. Additions and corrections to our knowledge of the endemic amphibians of São Tomé́ and Príncipe.'' Proceedings of the California Academy of Sciences, 55, 573-587.

Gilbert C.M., Bell R.C. (2018). ''Evolution of advertisement calls in an island radiation of African reed frogs.'' Biological Journal of the Linnean Society, 123(1), 1–11. [link]

Schick S, Kielgast J, Rödder D, Muchai V, Burger M, Lötters S. (2010). ''New species of reed frog from the Congo basin with discussion of paraphyly in Cinnamon-belly reed frogs.'' Zootaxa, 2501(1), 23-36. [link]

Species Account Citation: AmphibiaWeb 2020 Hyperolius thomensis: Sao Tome Giant Treefrog <https://amphibiaweb.org/species/611> 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.

AmphibiaWeb's policy on data use.