Drewes' Reed Frog

Hyperolius drewesi is a slender-bodied reed frog endemic to the Príncipe Island in the Gulf of Guinea. Described from 17 males and one female, their male snout-vent range 24.8 – 30.9 mm and their female snout-vent length is 32.7 mm. The head is wider than long. The short snout is obtusely pointed in dorsal view and round in profile. They have lateral nostrils that are visible in the dorsal view and closer to tip of snout than eye. The distinct canthus rostralis is slightly constricted behind nostrils. The loreal region is concave and oblique. The interorbital distance is greater than width of upper eyelid. The eye diameter is less than snout length. The pineal body not visible. The indistinct, round tympanum is half of eye diameter while the raised tympanic annulus is visible on anterior and ventral margin (Bell 2016). The arm lacks an ulnar tubercle and the hands do not have metacarpal, palmar, or thenar tubercles. All the fingers have expanded tips with circummarginal grooves. The disc on Finger III has a width ~1.6 times that of the phalanx. The relative finger lengths are I < II < IV < III. There are round subarticular tubercles on Fingers I – IV and an additional distal bifud tubercle on Finger IV. The finger webbing formula is I 2 – 2 II 2 – 3 II 2 – 1 IV. No nuptial pads were observed (Bell 2016). The plantar has a smooth surface with a distinct, oval inner metatarsal tubercle and an ill-defined outer metatarsal tubercle. All five toes have expanded tips with Toe IV having a disc width that is ~1.5 times that of the phalanx. The toes have relative lengths of I < II < III < V < IV and well-developed, round subarticular tubercles. The toe webbing formula is I 1 – 1 II ½ – 1 III 0 – 1 IV 1 – 0 V (Bell 2016). The skin on dorsum is finely granular with fine dorsal asperities while the skin on limbs smooth. There is no dorsolateral fold. The skin on ventral surface is initially smooth at the anterior region and becomes increasingly granular towards the posterior region. The vocal sac is positioned medially. There is a small, rounded gular gland that occupies less than half of gular area (Bell 2016). Hyperolius drewesi can be differentiated from other reed frogs of the region based on location, coloration, and morphology. More specifically, H. drewesi is the only Reed frog found on Príncipe Island. It is sexually monochromatic (both sexes are 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 drewesi differs from H. thomensis in male body size (H. drewesi has a snout-vent length of 25 – 31 mm, H. thomensis has a snout-vent length of 36 – 41 mm), in the distal portion of the terminal phalanx (H. drewesi is disc shaped, H. thomensis is oval with the wider portion in horizontal plane), and in ventral coloration (H. drewesi is white to translucent while H. thomensis is marbled black/orange; Bell 2016). Hyperolius drewesi differs from H. molleri by the former lacking a black contour along the edges of the green/yellow band of coloration that extends down the dorsal side of the thigh (always present in H. molleri), and by lacking red/orange coloration on the dorsal and ventral sides of the thigh (always present in H. molleri; Bell 2016). In life, the iris of H. drewesi is gold. The dorsum, dorsal surface of forelimb and hindlimb, and side of the head are green. The dorsal asperities lighter colored. The dorsal surface of thigh is translucent with thin green medial band extending from dorsum to lower limb. The dorsal surface of fingers and toes are green. The ventral surfaces are translucent, but the is chest white. In preservative, the dorsum becomes light gray with lighter asperites while the side of head and the dorsal surface of forelimb and hindlimb become cream with fine black speckling. The ventral surfaces are cream (Bell 2016). Hyperolius drewesi exhibits sexual dimorphism with the sole female specimen from the species description being larger than males and with males having a round gular gland that occupies less than half of gular area, a vocal sac, and dorsal asperities. There is also developmental variation with juvenile coloration (“phase juvenile”) resembling the juvenile coloration in H. cinnamomeoventris (tan with bright yellow dorsolateral lines; Bell 2016).The species authority is: 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.Multilocus molecular data indicate that H. drewesi is in the genus Hyperolius and is part of the H. cinnamomeoventris species complex, which at the time of the species' description, included 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, Bell 2016, Bell et al. 2017).The species epithet, “drewesi” is an acknowledgement of Robert C. Drewes and his extensive contributions to herpetological research in Africa and in particular, his contributions to documenting biodiversity in São Tomé and Príncipe (Bell 2016).

Hyperolius drewesi is known from twenty localities on Príncipe Island spanning much of the altitudinal and ecological variation across the island, including disturbed habitats, at elevations of 0 – 650 m (Bell 2016).

Hyperolius drewesi are commonly found during visual surveys at night approximately 1 – 2 m above the ground on leaves and thin branches overhanging streams or small pools of standing water (Bell 2016).Hyperolius drewesi breed near slow-moving streams and temporary ponds in primary forest and in marginal habitats with high levels of human disturbance (Bell 2016). As in many Hyperolius, females deposit eggs on the surface of leaves overhanging water. The eggs observed at the type locality were white with faint pigmentation on the animal pole and ~2 mm in diameter (Bell 2016).

Hyperolius drewesi is a species of frog in the family Hyperoliidae. It is endemic to the island of Príncipe in São Tomé and Príncipe. Common names include Oceanic tree frog and Drewes' reed frog. It is the only Reed frog found on Príncipe Island.