Ptychadena nana Perret, 1980

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 nana Perret, 1980

Ptychadena nana Perret, 1980: 160.

Rana (Ptychadena) nana - Dubois 1981: 233.

Ptychadena (Ptychadena) nana - Dubois 1992: 316.

Type material.

Holotype. A female (ZMB-26878 H) collected by O. Neumann and C. von Erlanger between June and mid-August 1900 (see Neumann 1902) in “Somaliland”, which corresponds to Didda, East Arussi plateau, Ethiopia, 2000-3000 m a.s.l. according to Largen and Perret ( Largen 1975, 1977; Perret 1980) [Coordinates estimated by Largen (1997): 7.83°N, 39.50°E]. Paratypes. From the 20 paratypes included in the original description ( Perret 1980), 16 specimens (ZMB-26877, ZMB-57185 up to and including ZMB-57199) collected by O. Neumann and C. von Erlanger at the same time and location are in the collections of the Berlin Museum and four have either been lost or placed in another collection.

Material examined.

Except for the type series, all the material examined is deposited at ZNHM. Beside the female holotype (ZMB-26878 H), we examined four female paratypes (ZMB-57189, ZMB-57190, ZMB-57193, ZMB-57199) and four male paratypes (ZMB-26877, ZMB-57191, ZMB-57192, ZMB-57195) collected by C. von Erlanger and O. Neumann in 1900 likely between June and mid-August in Didda, East Arussi plateau, one female (SB488) and two males (SB486, SB487) collected by S. Goutte and Y. Bourgeois on 26 June 2018 west of Ch’ange (8.1303°N, 39.3985°E, 2357 m a.s.l.), one female (SB493) and two males (SB494, SB495) collected by S. Goutte and Y. Bourgeois on 27 June 2018 between Robé and Sedika (7.7307°N, 39.7133°E, 2377 m a.s.l.), five females (SB508, SB510, SB512, SB515, SB516) and four males (SB523, SB524, SB525, SB526) collected by S. Goutte and Y. Bourgeois on 29 June 2018 southeast of Ch’ange (8.1086°N, 39.4486°E, 2573 m a.s.l.).

Diagnosis.

The smallest species (male (12) SVL 28.3 ± 3.3 mm, female (12) SVL 29.6 ± 3.2 mm) of the P. neumanni complex (Fig. 15 ), distinguished by the following combination of characters: (1) short hind limbs (male TL/SVL 0.45 ± 0.03, female TL/SVL 0.44 ± 0.03), (2) short hands (HAL/SVL 0.20 ± 0.02), (3) short feet (male FL/SVL 0.49 ± 0.04, female FL/SVL 0.48 ± 0.04), (4) reduced foot webbing, (5) no stripe or blotch on the tympanum, (6) adult males almost always covered in small warts during the breeding season.

Comparison.

Distinguished from all Ethiopian Ptychadena , except for P. robeensis sp. nov., by a considerably smaller size. Very similar to P. robeensis sp. nov., P. nana has relatively shorter hand, shorter head, a shorter eye-tympanum distance and shorter feet than P. robeensis sp. nov. The tympanum lacks any light marking, as opposed to P. robeensis sp. nov. Small warts almost always present in males, whereas they are absent in P. robeensis sp. nov.

Description of the holotype.

Small sized (SVL 26.9 mm) gravid female with short hind limbs (TL/SVL 0.43, Fig. 16 , Suppl. material 3: Table S1). Head longer than wide (HW/HL 0.95). Snout rounded, slightly projecting beyond the lower jaw. Interorbital distance 0.58 × eye diameter. Nostril half-way between the tip of the snout and the eye. Internarial distance 1.4 × interorbital distance. Tympanum 0.65 × eye diameter. Finger tips not expanded but rounded. Finger formula: III<IV<III. Hand free of webbing. Hindlimbs short, with tibia length 0.42 × snout-vent length. Foot 1.2 × tibia length and 1.3 thigh length. Toe tips rounded. Outer metatarsal tubercle 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(1-2), IVi/e(2-2), Vi(2). Ridges hardly distinguishable due to the state of preservation of the specimen.

Coloration of the holotype in preservative.

Dorsal ground color brown with irregular oval dark brown blotches symmetrically distributed, presumably on the dorsolateral ridges. One dark brown blotch on each upper eyelid. No vertebral stripe. One fainted dorsolateral cream ridge on each side. Dark brown canthal stripe from the tip of the snout to the back of the jaw. Upper lip cream. Flanks brown to dark brown with numerous cream spots which merge ventrally. Throat, ventrum, ventral side of tibias uniformly cream without any melanization. Ventral side of the thighs light brown. Dark brown bars on the thighs, tibias and feet. Back of the thighs brown marbled with cream. Dark brown irregular markings on the arms and forearms. No stripe or blotch on the tympanum.

Variations.

As the other members of the Ptychadena erlangeri species group, Ptychadena nana shows color polymorphism. In life, dorsum coloration varies from light grey to sand and brown. The dark blotches disposed more or less symmetrically on the dorsum vary in size and number, sometimes covering more than half the dorsum. Their colors vary from olive-brown, with some green iridescence, to black. One or several blotches of the same color, sometimes fused into a large irregular shape, were present on the anterior part of the flank in all examined specimens. The vertebral stripe, when present, may be thin, medium or wide and cream, light brown or bright green. Some individuals lack any vertebral stripe.

Iris bicolored, the upper third silver to golden and lower two thirds brown to dark brown. Upper and lower jaws cream, golden or light brown, often with irregular light grey or light brown markings but no barring. All specimens examined featured a dark brown canthal stripe from the tip of the snout to the back of the upper lip, sometimes dusted with small green spots. Tympanum uniformly colored and lacking any light stripe of blotch. A thin cream or light green longitudinal stripe on the tibia extending the complete 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 yellow or cream. Ventrum uniformly white. Throat white in females and pale yellow to deep yellow in adult males. Vocal sacs bicolored grey anteriorly and cream posteriorly, rarely completely grey. Small warts over the body and forelimbs present in 90% of adult males examined.

Habitat, distribution, and natural history.

Ptychadena nana is found on the eastern half of the Arussi plateau (7.64-8.30°N, 39.39-39.87°E, Oromia, Ethiopia from 2380 to 2850 m a.s.l. In the south, its range is limited by the Shebelle River, while in the northeast it is bordered by the Great Rift Valley. The westernmost individuals were found around four kilometers west of Ch’ange. The steep terrain just east of Huruta may serve as geographic barrier for dispersal in this species, as it has not been found further southeast. In the southwest end of its range, P. nana has been found just north of Dibe, but presumably occurs all the way down to Barbari as there is no physical barrier that would prevent its dispersal on this side of the plateau.

Males are found calling at night in large numbers from shallow roadside puddles, usually overgrown by grass. Within the genus, P. nana is found in sympatry with Ptychadena cooperi .

Advertisement call.

The call of Ptychadena nana (5 males, 56 calls) is composed of a single pulsed note of 205 ± 47 ms in duration, containing 16.9 ± 2.8 pulses. Inter-pulses intervals are very short (9 ± 2 ms) and irregular, forming few irregular pulse groups and resulting in a high pulse rate (84 ± 10.2 pulses s-1). Call peak frequency is 2461 ± 26 Hz.

The call of P. nana can be differentiated from those of P. cooperi , P. amharensis , P. doro sp. nov. and P. neumanni (types A and B) by the distinguishable pulses composing the calls. It is also distinct form the calls of P. delphina sp. nov. and P. robeensis sp. nov. by its short inter-pulse intervals. Finally, the call of P. nana differs from the calls of P. delphina sp. nov., P. robeensis sp. nov., P. erlangeri , P. levenorum , P. beka sp. nov., and P. goweri by its short duration and high pulse rate.

Figures

Figure 15. Ptychadena nana A live male (SB 494; left) and female (SB 488, right) B dorsal and ventral views of the same individuals (male left, female right) after euthanasia and before fixation.

Figure 16. Type specimens of Ptychadena nana. Dorsal and ventral views of three specimens from the type series A female holotype (ZMB- 26878 H) B male paratype (ZMB- 57191) C female paratype (ZMB- 57193).