Ptychadena robeensis, Goutte & Reyes-Velasco * & Freilich & Kassie & Boissinot, 2021

Goutte, Sandra, Reyes-Velasco *, Jacobo, Freilich, Xenia, Kassie, Abeje & Boissinot, Stephane, 2021, Taxonomic revision of grass frogs (Ptychadenidae, Ptychadena) endemic to the Ethiopian highlands, ZooKeys 1016, pp. 77-141 : 77

Ptychadena robeensis sp. nov.

Type material.

Holotype. Adult male (SB81) collected on 9 April 2018 by S. Goutte and J. Reyes-Velasco between Robe and Ali (7.2111°N, 39.9672°E, 2374 m a.s.l.). Paratypes. Three males (15-139, 15-140 and 15-147) and one female (15-138) collected on 8 August 2015 northwest of Robe (7.1720°N, 39.9722°E; 2431 m a.s.l.), one male (15-163) collected on 9 August 2015 east of Dinsho (7.1061°N, 39.8182°E; 3058 m a.s.l.), one male (16-92) and one female (16-77) collected by J. Reyes-Velasco and S. Boissinot 10 July 2016 east of Dinsho (7.1065°N, 39.8184°E, 3065 m a.s.l.), one male (SB65) collected by J. Reyes-Velasco and S. Goutte on 8 April 2018 south of Dinsho (7.0915°N, 39.7834°N, 3079 m a.s.l.), three males (SB82, SB83, SB84) collected by J. Reyes-Velasco and S. Goutte on 9 April 2019 between Robe and Ali (7.2111°N, 39.9672°E, 2374 m a.s.l.), three males (SB88, SB92, SB93) and two females (SB87, SB89) collected by J. Reyes-Velasco and S. Goutte on 9 April 2019 east of Dinsho (7.1056°N, 39.8168°E, 3015 m a.s.l.). All specimens are deposited at ZNHM.

Diagnosis.

Small species (male (13) SVL 30.3 ± 0.7 mm, female (4) SVL 31.6 ± 2.9 mm) of the Ptychadena erlangeri species group (Fig. 17 ), distinguishable from other species of the P. neumanni complex by the following combination of characters: (1) short hind limbs (male TL/SVL 0.45 ± 0.0.03, female TL/SVL 0.44 ± 0.02), (2) short forearms (male FLL/SVL 0.18 ± 0.02, female FLL/SVL 0.18 ± 0.00), (3) short feet (male FL/SVL 0.5 ± 0.03, female FL/SVL 0.49 ± 0.05), (4) reduced foot webbing, (5) a vertical cream or golden stripe or blotch on the tympanum (sometimes faint), (6) warts absent in adult males during the breeding season.

Comparison.

Distinguished from all Ethiopian Ptychadena , except for P. nana , by a considerably smaller size. Compared to P. nana , it has relatively longer hands, greater eye-tympanum distance and longer feet. Ptychadena robeensis sp. nov. also presents a more or less distinct cream or golden blotch on the tympanum, which is absent in P. nana . Finally, the bodies of adult male P. robeensis sp. nov. are not covered in warts as opposed to P. nana .

Description of the holotype.

Small sized (SVL 29.3 mm) male with short hind limbs (TL/SVL 0.45, Fig. 17 , Suppl. material 3: Table S1). Head longer than wide (HW/HL 0.96). Snout slightly rounded, projecting beyond the lower jaw. Interorbital distance equal to the eye diameter and to the internarial distance. Nostril half-way between the tip of the snout and the eye. Tympanum 0.77 × eye diameter. Finger tips not expanded but rounded. Finger formula: I<II<IV<III. Hand free of webbing. Hindlimbs short, with tibia length 0.45 × snout-vent length. Tibia and thigh lengths equal. Foot 1.3 × tibia length. Toe tips rounded. Inner metatarsal tubercle present, outer absent. Toe formula: I<II<V<III<IV. Foot webbing formula (toe internal/external sides, number of phalanges webbed): Ie(1), IIi/e(1-1), IIIi/e(1-1), IVi/e(1-1), Vi(1). Four continuous dorsal ridges and one faint cream lateral ridge, interrupted on one side and continuous on the other.

Coloration of the holotype in life.

Dorsal ground color grey with a few, elongated dark brown blotches symmetrically distributed on the dorsolateral ridges. Thin cream stripe on the dorsum from the tip of the snout to the vent, on the foot, tibia, and half of the thigh. Dark olive brown canthal stripe from the tip of the snout to the back of the jaw. Small cream blotch on the otherwise dark brown tympanum. Upper and lower lip cream to light brown towards the tip of the snout with irregular small brown markings.

Iris bicolored, with upper third light cream, and the lower two thirds dark brown with golden freckles. Irregular dark brown blotches on the flanks. Ventrum cream, reticulated with light brown on its lower part. Throat light yellow. Two small symmetrical dark brown blotches on the antero-ventral side of the shoulders. Hind limbs brown with dark brown bars over the thighs, tibias and feet. A few very small round white dots around the groin. Back of the thighs dark brown irregularly molted with yellow. Vocal sacs dark grey anteriorly and light grey posteriorly.

Coloration of the holotype in preservative.

Dorsal ground color grey with a few large oval black blotches symmetrically distributed on the dorsolateral ridges. Thin cream vertebral stripe from the tip of the snout to the vent. Dark brown canthal stripe from the tip of the snout to the back of the jaw. Faint vertical stripe on the otherwise brown tympanum. Upper lip and lower lips cream dusted with light grey. Flanks light with a few irregular small dark brown blotches. Throat, ventrum, ventral side of the thighs and tibias uniformly cream. Two symmetrical brown blotches on the ventral side of the shoulders. Faint, thin longitudinal stripe on the tibia, foot and half of the thigh. Foot, tibia and thigh barred with brown. Back of thighs molted light grey and brown. Vocal sacs dark grey anteriorly and light grey posteriorly. Nuptial pads cream.

Variations.

As the other members of the Ptychadena erlangeri species group, Ptychadena robeensis sp. nov. shows color polymorphism. In life, dorsum coloration varies from grey-brown to reddish or yellowish brown, or bright lime green. The dark blotches disposed more or less symmetrically on the dorsum vary in size and number and are either dark brown or black. A few individuals completely lack melanization on the dorsum, resulting in an almost uniform light brown or bright lime green coloration. The limbs of these individuals, however, have melanization patterns comparable to other individuals.

One or a few dark blotches is present on the anterior part of the flank of some individuals.

The vertebral stripe, when present, may be thin or wide and cream, sand, yellow or bright lime green. Wide stripes may be doubled with a thin, lighter line. Some individuals lack any vertebral stripe and individuals lacking dorsal melanization generally have a barely visible thin light vertebral stripe.

Iris bicolored, the upper third cream, silver or golden and lower two thirds brown to dark brown. Upper and lower jaws cream, golden or light green, often with irregular light grey or light brown markings but no barring. Most individuals feature a dark brown canthal stripe from the tip of the snout to the back of the upper lip, sometimes dusted with small green spots. Individuals lacking dorsal melanization have a golden canthal stripe covered with small dark grey spots. Interestingly, the nostrils of these individuals are outlined in black. Tympanum dark brown with a more or less defined cream to golden vertical blotch. A thin cream or light green longitudinal stripe on the tibia extending to half or the whole length of the thigh is present in some individuals. Barring on the tibias, thighs and feet may be very distinct or almost completely absent. Thighs posteriorly marbled with dark brown and light brown, yellow or light green. Ventrum uniformly white. Throat white or very pale yellow in females and pale to deep yellow in adult males. Vocal sacs dark grey in 70% of examined specimens, bicolored dark grey anteriorly and light grey posteriorly in some individuals, and rarely light grey. Warts were absent from all adult males examined.

Etymology.

The specific name refers to the town of Robe, near the type locality.

Habitat, distribution and natural history.

Ptychadena robeensis sp. nov. occupies a very small range (7.05-7.23°N, 39.78-39.98°E) around the town of Robe, Bale zone, Oromia, Ethiopia. It is found at elevations ranging from 2375 m to 3120 m a.s.l. The westernmost individuals were found near Dinsho, which is also the highest elevation point of the species range. In the south, P. robeensis sp. nov. is found between Robe and Goba, while it is known up to just west of Ali in the north. The species presumably occurs further north on the plateau as elevation and habitat seem rather homogeneous up to the Shebelle River.

Males are found calling at night from shallow grassy puddles or flooded cultivated fields. Calling activity typically starts after 22:00, even though males may be at calling sites earlier. Males have been found calling in syntopy with P. cooperi and P. levenorum . Genetic analyses have shown that P. levenorum and P. robeensis sp. nov. hybridize where their ranges overlap.

Advertisement call.

The call of Ptychadena robeensis sp. nov. (5 males, 101 calls) is composed of a single pulsed note of 534 ± 53 ms in duration, containing 9.8 ± 1 regularly-spaced pulses. Pulse amplitude increases gradually until 292 ± 19 ms, after what it decreases. Call peak frequency is 2876 ± 74 Hz with a slight increase in frequency within the call.

The call of P. robeensis sp. nov. can be distinguished from the calls of all other members of the P. neumanni complex, except for P. delphina sp. nov., by its regularly spaced pulses and long inter-pulses intervals (57 ± 5 ms). A higher frequency allows discriminating the calls of P. robeensis sp. nov. and P. delphina sp. nov.

Figures

Figure 17. Ptychadena robeensis sp. nov. A live male holotype (SB 81; left) and female paratype (SB 89, right) B dorsal and ventral views of the male holotype (SB 81; left) and a female (SB 69; right) after fixation. The female SB 69, green in life, lacks any melanization on the dorsum, a rare phenotype that has been encountered in a few individuals only.