Ptychadena erlangeri (Ahl, 1924)

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 erlangeri (Ahl, 1924)

Rana erlangeri Ahl, 1924: 4.

Ptychadena erlangeri - Perret 1980: 151-168.

Rana (Ptychadena) erlangeri - Dubois 1981: 233.

Ptychadena (Ptychadena) erlangeri - Dubois 1992: 316.

Ptychadena largeni Perret 1994: 67.

Type material.

Holotype. A gravid female (ZMB-26887) collected by C. von Erlanger in December 1900 at lake Abaya, Ethiopia (likely the eastern shore of the lake, 1300 m a.s.l., see remarks below).

Material examined.

Except for the type specimen and the type series of P. largeni , all the material examined is deposited at ZNHM. One female (15-47) collected by X. Freilich, J. Reyes-Velasco and S. Boissinot south of Assela (7.9068°N, 39.1238°E, 2520 m a.s.l.), one male (15-400) collected by X. Freilich, J. Reyes-Velasco and S. Boissinot on 22 August 2015 north of Fitche (9.7877°N, 38.6974°E, 2821 m a.s.l.), two males (15-417 and 15-420) collected by X. Freilich, J. Reyes-Velasco and S. Boissinot on 26 August 2015 north (6.3844°N, 38.5927°E, 2655 m a.s.l.) and south (6.3256°N, 38.6645°E, 2684 m a.s.l.) of Bore, respectively, one male (16-6) collected by J. Reyes-Velasco and S. Boissinot on 4 July 2016 between Addis Ababa and Ambo, eight males (16-6, 16-10, 16-11, 16-12, 16-14, 16-16, 16-17 and 16-24) collected by J. Reyes-Velasco and S. Boissinot on 5 July 2016 south of Assela (7.7776-7.8431°N, 39.1384-39.1529°E, 2553-2637 m a.s.l.), one female (16-131) and six males (16-99, 16-106, 16-112, 16-113, 16-114 and 16-118) collected by J. Reyes-Velasco and S. Boissinot on 12 July 2016 southeast of Mehal Meda (9.9894-10.3316°N, 39.7452-39.8092°E, 3017-3394 m a.s.l.), one female (16-142) and one male (16-155) collected by J. Reyes-Velasco and S. Boissinot on 13 July 2016 north of Debre Birhan (9.6822-9.6979°N, 39.5505-39.5628°E, 2833-2837 m a.s.l.), one male (16-166) collected by J. Reyes-Velasco and S. Boissinot on 14 July 2016 south of Fitche (9.7502°N, 38.7445°E, 2726 m a.s.l.), one female (SB231) and one male (SB232) collected by S. Goutte and J. Reyes-Velasco on 23 April 2018 south of Gumer (7.9125°N, 38.0644°E, 2831 m a.s.l.), two males (SB552 and SB553) collected by S. Goutte and Y. Bourgeois on 3 July 2018 east of Mehal Meda (10.3247°N, 39.8092°E, 2795 m a.s.l.), one male (SB562) collected by S. Goutte and Y. Bourgeois on 4 July 2018 east of Mehal Meda (10.3247°N, 39.8092°E, 2795 m a.s.l.), three males (SB570, SB571 and SB577) collected by S. Goutte and Y. Bourgeois on 7 July 2018 north of Gebre Guracha (9.8818°N, 38.3660°E, 2558 m a.s.l.), one male (SB615) collected by S. Goutte and Y. Bourgeois on 14 July 2018 near Holeta (9.0692°N, 38.5214°E, 2397 m a.s.l.), P. largeni male holotype (MHNG-2513.31), P. largeni male paratypes (MHNG-2513.38, MHNG-2513.42, MHNG-2513.44, MHNG-2513.45, MHNG-2513.49, MHNG-2513.52), P. largeni female paratypes (MHNG-2513.56, MHNG-2513.57, MHNG-2513.58, MHNG-2513.59 and MHNG-2513.60) collected by M. Largen on 12 June 1977 in Addis Ababa, Shewa (Shoa) (9.03°N, 38.75°E, 2500 m a.s.l.).

Diagnosis.

A medium-sized (male (35) SVL 34.1 ± 2.5 mm, female (10) SVL 34.6 ± 1.7 mm) member of the Ptychadena erlangeri species group (Fig. 11 ). Ptychadena erlangeri differs from other members of the P. neumanni complex by the following combination of characters: (1) relatively short hind limbs (male TL/SVL 0.53 ± 0.04, female TL/SVL 0.54 ± 0.05), (2) tympanum translucent, without any light bar or blotch, (3) vocal sacs light in color, from cream to light grey, very rarely with a bit of grey, (4) adult males with robust forelimbs, (5) adult males often covered in small warts.

Comparison.

Species very variable in body size across its range, but always smaller than P. cooperi , P. goweri and larger than P. nana and P. robeensis sp. nov. Ptychadena erlangeri can be distinguished from P. beka sp. nov., P. delphina sp. nov., P. doro sp. nov., P. amharensis , P. neumanni , and P. robeensis sp. nov. by the absence of light bar or blotch on the tympanum. Furthermore, adult males can be distinguished by their cream or light-yellow vocal sac from P. beka sp. nov., P. neumanni , P. robeensis sp. nov., P. doro sp. nov., and P. delphina sp. nov. Ptychadena erlangeri has a shorter snout than P. amharensis , P. harenna , P. beka sp. nov., P. delphina sp. nov., P. goweri , P. cooperi , and P. doro sp. nov. Finally, P. erlangeri can be distinguished from P. levenorum by longer eye-nostril and inter-orbital distances and longer hind limbs.

Description of the holotype.

Medium sized (SVL 37.6 mm), slender, gravid female with long hind limbs (TL/SVL 0.63, Fig. 12 , Suppl. material 3: Table S1). Head longer than wide (HW/HL 0.94). Snout pointed, 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 1.2 × interorbital distance. Tympanum 0.61 × eye diameter. Finger tips not expanded but rounded, with moderate subarticular tubercles. Finger formula: I<II<IV<III. Hand free of webbing. Hindlimbs elongated, with tibia length 0.63 × snout-vent length. Rounded white warts irregularly spread on the dorsal side of tibia. Foot as long as thigh and almost as long as tibia (FL/TL 0.98). Toe tips rounded. Subarticular tubercles small and round. Inner metatarsal tubercle present, external absent. Toe formula: I<II<III<V<IV (right foot) and I<II<VIII<IV (left foot). Foot webbing formula (toe internal/external sides, number of phalanges webbed): Ie(1), IIi/e(1-2), IIIi/e(2-2), IVi/e(2-2), Vi(2). Two light, continuous lateral ridges, four interrupted dorsal ridges. No vertebral nor sacral ridges. Note that we did not see the nasal ridges that Perret (1980) noted as the single major diagnostic character for the species.

Coloration of the holotype in preservative.

Although the holotype is in overall very good condition, the coloration seems to have faded away with time and some dark markings noted by Ahl (1924) in the original description and Perret (1980) are now barely visible or have vanished altogether. Dorsal ground color light brown with irregular oval dark brown 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. Upper lip and flanks cream. The dark markings on the upper and lower lips noted by Ahl (1924) are no longer visible. Throat, ventrum, ventral side of the thighs, and tibias uniformly cream without any melanization. A thin, cream longitudinal stripe on the tibias and half of the thighs. Dark brown bars on the tibias and brown markings on the thighs.

Variations.

Ptychadena erlangeri shows important variations in body size, morphology, and coloration across its large distribution range. South of the GRV, individuals of P. erlangeri are generally larger (male (9) SVL 36.8 ± 1.9 mm, female (1) SVL 35.6) than north of the GRV (male (17) SVL 33.5 ± 1.9 mm, female (3) SVL 35.4 ± 1.2). Morphometric variations are summarized in Table 1 .

In life, dorsum coloration varies from dark brown to grey-brown, olive and golden, sometimes with irregular green blotches. All specimens examined had small dark brown or black blotches distributed symmetrically on the dorsal ridges. A few additional dark brown or black blotches are found in the anterior part of the flanks. A vertebral stripe is always present, either thin or wide and may be white, cream, or green.

Iris bicolored, the upper third silver and lower two thirds dark brown. Upper and lower jaws featuring irregular light grey or 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, with the tympanum uniformly colored and lacking any light stripe of blotch. A thin cream longitudinal stripe on the tibia extends to a fifth to the whole length of the thigh. Tibias, thighs, and feet more or less regularly barred with dark brown. Thighs posteriorly marbled with dark brown and yellowish brown. Ventrum and throat uniformly cream to yellow. Vocal sacs cream, yellowish or light grey, very rarely with a bit of grey. Small warts over the body and forelimbs present in 80% of adult males examined.

Habitat, distribution, and natural history.

Ptychadena erlangeri has a wide distribution range extending on both sides of the Great Rift Valley (6.23-10.33°N, 38.06-39.81°E). It is restricted to higher altitudes, from 2387 m to 3394 m a.s.l. (based on 156 barcoded individuals). West of the Great Rift Valley, its range is limited by the Blue Nile valley and specimens have been found just north of Gebre Guracha. Its northernmost locality is Mehal Meda. Southeast of the GRV, populations have been found near Assela, Kofele and Irba Moda. A few individuals have been found in the southwest, between Tippi and Gech’a, and at lower elevation than any other population (7.4512°N, 35.3992°E, 2270 m a.s.l.). GPS coordinates for all examined specimens are given in Suppl. material 3: Table S1. Ptychadena erlangeri is found in syntopy with P. beka sp. nov. at the lower end of its altitudinal range, notably near Fitche, Holeta, between Ambo and Wonchi, and possibly near Assela. It is also found in sympatry with P. cooperi across its range.

Males are found calling in shallow puddles, flooded grasslands, or agricultural fields. Males can be found vocalizing very close to one another, sometimes in important numbers. Calling activity depends on rainfall and is highest during rainy months. Calling usually starts after 22:00, and sometimes as late as 02:00 in dry weather, and ceases before dawn. Numerous, small bicolored eggs are laid in the same water body.

Advertisement call.

The call of Ptychadena erlangeri (5 males, 226 calls) is composed of a single pulsed note of 290 ± 35 ms in duration, containing 46.5 ± 1.6 pulses. Within calls, pulses are grouped, with 4.1 ± 2.5 pulses per group and the first pulse typically notably lower in amplitude than the other pulses of the pulse group. Amplitude of the call increases gradually during most of the call, peaking at 230 ± 14 ms, and decreases abruptly afterwards. Call dominant frequency is 2343 ± 454 Hz.

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

Remarks.

Confusion and difficulty to distinguish P. erlangeri from P. neumanni arose from the original descriptions of the species themselves, both published by Ahl in 1924 in the same article. The original description of P. neumanni , based on 35 syntypes, most likely contained three distinct species ( Perret 1980), while P. erlangeri was described based on a single gravid female. Perret (1980) restricted P. neumanni to three male syntypes. Comparing the two closely related species was thus rendered near impossible due to the low sample size and the fact that each species was represented by specimens of different sexes. Adding to the confusion, in 1994, Perret described Ptychadena largeni from 30 specimens from Addis Ababa, Shewa (Shoa) sent to him by Largen as Ptychadena erlangeri . Largen (1997) then considered that the morphological diagnostic characters found by Perret in the 30 specimens were due to conservation artefacts as these individuals were fixed in alcohol rather than in formalin, and subsequently synonymized P. largeni with P. neumanni in 2001, even though he had originally considered those specimens to belong to P. erlangeri . Recently, molecular phylogenetic analyses grouped the holotype of P. largeni with that of P. erlangeri ( Reyes-Velasco et al. in review).

Largen (2001) thus included a population of P. erlangeri ( P. largeni ) in P. neumanni , along with specimens from Debre Markos, Gondar, the Bale Mountains, etc. and included specimens from the Harenna forest and Debre Markos in P. erlangeri . The two groupings thus comprised specimens of several species, many of which placed in both groups (Fig. 1 ). As a result, Largen (2001) failed to give satisfactory diagnostic characters distinguishing P. erlangeri from P. neumanni as all the given characters largely overlapped, and later authors relied heavily on the distribution ranges given by Largen to assign species names to the populations they sampled. Notably, the photos presented in Largen and Spawls (2010) for P. erlangeri is in fact most likely a P. goweri (Yadot River, close to Dolo Mena described as the “large” form occurring in Bale Mountain by Largen 1997), and the specimens presented as P. neumanni are in fact P. erlangeri .

Figures

Figure 1. Species included under the names Ptychadena neumanni and P. erlangeri in previous studies. Species names within the circles correspond to the revised taxonomy. Left (yellow) and right (blue) circles contains all species identified as P. neumanni and P. erlangeri, respectively, since their original descriptions Ahl (1924). Species at the intersection of the two circles were identified as both species either in different studies (e. g., Largen 2001; Freilich et al. 2014; Smith et al. 2017 a, b; Reyes-Velasco et al. 2018) or within the same study (e. g., Largen 2001). The full taxonomic history of the group is summarized in Suppl. material 3: Table S 6.

Figure 11. Ptychadena erlangeri A live male (SB 571; left) and female (SB 548, right) B dorsal and ventral views of the same individuals (male left, female right) after euthanasia and before fixation.

Figure 12. Holotype of Ptychadena erlangeri. Dorsal and ventral views of the female holotype (ZMB- 26887).