Pristimantis nimbus, Sánchez-Nivicela, 2017

Sánchez-Nivicela, Juan C., 2017, A new terrestrial frog (Anura: Craugastoridae) from the montane cloud forests of the southeastern Ecuadorian Andes, Zootaxa 4318 (3), pp. 520-530 : 521-527

Pristimantis nimbus new species

Figs. 2–5 |

Holotype. MZUA.AN.1475, an adult male, collected on 19 September 2015 by Juan C. Sánchez, Veronica L. Urgiles and Bruno A. Timbe at the Ecological Conservation Area Tinajillas-Río Gualaceño, (3°0’0.29’’S; 78°30’34.47’’W; 2399 masl), Provincia Morona Santiago, Ecuador ( Fig. 1 ).

Paratopotypes. MZUA.AN. 1462, 1465, 1466, 1468 (adult males) and MZUA.AN.1472, 1483 (subadult males), collected with the holotype.

Paratypes. MZUA.AN.0705, a sub-adult male collected on 10 October 2013 by Veronica L. Urgiles and Cristian Nieves at the Área Ecológica de Conservación Tinajillas Rio Gualaceño (3°1’47.20’’S; 78°35’3.43’’W; 2273 masl), Provincia Morona Santiago, Ecuador.

Diagnosis. Due to a lack of morphological synapomorphies for Pristimantis ( Hedges et al. 2008; Padial et al. 2014), we tentatively assign the new species to this genus based on morphological similarity to other species in this clade. Pristimantis nimbus ( Figs. 2–4 ; Table 1) is a small species characterized by: (1) skin of dorsum finely shagreen with scattered low and small tubercles, flanks areolate, being more noticeable towards the ventral region, skin on venter finely areolate, lacking dorsolateral and discoidal folds; (2) tympanic membrane and annulus differentiated, visible, rounded (42% of eye diameter), supratympanic fold present, one or two postrictal tubercles; (3) short snout, subacuminate in dorsal view, rounded in profile, lacking tubercles on the tip, canthus rostralis slightly concave; (4) upper eyelid bearing one or two small subconical tubercles and several scattered low tubercles, cranial crests absent; (5) dentigerous process of vomer prominent, slightly oval with three to seven teeth, rounded choana; (6) nuptial pads present, vocal sac and vocal slits absent; (7) finger I shorter than II, discs on all fingers laterally but moderately expanded; (8) fingers bearing narrow lateral fringes; (9) ulnar tubercles low, one diffuse antebrachial tubercle, palmar tubercles low and small; (10) heel with one subconical tubercle, shank lacking tubercles, tarsal tubercles low and small; (11) toes bearing narrow lateral fringes; webbing absent; toe V longer than III; discs of toes moderately expanded; (12) inner metatarsal tubercle ovoid three times bigger than outer one, rounded; supernumerary plantar tubercles present, rounded, smaller than subarticular tubercles; (13) iris greenishcream with thin dark brown flecks and horizontal reddish copper stripe, dorsal coloration varies from copperbrown with few dark brown and green marks to brown with greenish-brown; flanks are cream with dark brownish flecks, ventral coloration is dusty brown with dark brown flecks; groin, thighs, posterior portion of flanks, and arm insertion with bright yellow to orange oval-shaped flash marks surrounded by dark brown to black marks forming a reticulated pattern; (14) SVL in adult males 23.9 mm ±2.9 (range: 22.4–28.6).

Comparison with similar species. Pristimantis nimbus is similar to other species of Pristimantis from north eastern Ecuador and northern Peru which have distinctive flash marks on the groin and lack cranial crests: Pristimantis altamazonicus , P. ardyae , P. bambu , P. bellator , P. caeruleonotus , P. cethospilus , P. churuwiai , P. croceoinguinis , P. cryptomelas , P. diadematus , P. flavobracatus , P. gualacenio , P. nigrogriceus , P. ventrimarmoratus and P. versicolor . However, Pristimantis altamazonicus differs from the new species by lacking tubercles on tarsus and heel, and by having reddish to orange inguinal coloration with bold black bars and blotches. Pristimantis ardyae differs from P. nimbus by lacking ulnar tubercles and by the amber with dark orange spots dorsal coloration (brownish to olive green in P. nimbus ) and finely granular skin. Pristimantis bambu lacks a tympanic membrane and tubercles on tarsus and heel. Pristimantis bellator differs from the new species by having a smooth dorsal skin with scattered tubercles, small tubercles on the upper eyelids (one or two subconical in P. nimbus ) and basal webbing on feet. Pristimantis caeruleonotus differs from the new species by having smooth dorsal skin with scattered spicules, dorsolateral folds, a tubercle in the tip of the snout and black inguinal coloration with white and pale blue spots. Pristimantis ceuthospilus differs from P. nimbus by lacking tubercles on the heel and by having a sharper snout and large orange to yellow spots on the posterior surfaces of thighs, which are not outlined by black or brown. Pristimantis gualacenio differs from the new species by lacking dentigerous process and conspicuous conical tubercles on the dorsum, eyelids, tarsus, heel and ulna, while P. cryptomelas differs from the new species by lacking nuptial pads and by presenting conspicuous dermal ridges on the head, occipital region and anterior part of dorsum, and by having large conical tubercles on the tarsus and heel. Pristimantis versicolor differs from P. nimbus by lacking tubercles on the heel and by presenting a brownish to black groin coloration with red-pinkish flecks (dark brown with bright yellow spots in P. nimbus ). Pristimantis churuwiai differs from the new species by having dorsolateral folds, an internarial tubercle and a finely granular dorsal skin. Furthermore, Pristimantis churuwiai is only known to occur at elevations between 1400 and 1800 masl. Pristimantis diadematus differs from the new species by lacking tubercles on ulna, tarsus and upper-eyelid and by having scapular folds and an inguinal coloration that varies from bluish-white, yellowish, pinkish or pale-green with dark brown diagonal bars. Besides, Pristimantis diadematus only occurs in the lowland tropical rainforest at elevations below 1700 masl. Likewise, P. ventrimarmoratus and P. nigrogriseus have been only registered at elevations below 1800 masl, and differ from the new species in that nuptial pads and tarsal tubercles are absent in P. nigrogriseus and the tympanic membrane and nuptial pads are absent in P. ventrimarmoratus .

MZUA MZUA MZUA MZUA MZUA Mean±SD

(range)

AN1475 AN1465 AN1462 AN1466 AN1468

Holotype Paratype Paratype Paratype Paratype

Description of the holotype. Adult male ( Figs. 2–4 ) with SVL 24.5 mm. The head is wider than long, head length 75% of the head width. Snout subacuminate in dorsal view and rounded in profile ( Fig. 4 C–D), eye-nostril length 11.71% of SVL. Canthus rostralis slightly concave in dorsal view, straight in profile view, nostrils laterally oriented; interorbital space flat, narrower than the upper eyelid, interorbital distance 82% of the upper eyelid. Cranial crests absent, upper eyelid with two subconical tubercles and five to eight low and small scattered tubercles. Tympanic membrane differentiated from the surrounding skin, tympanic annulus 42% of eye diameter. Two small rounded postrictal tubercles present. Small and round choanas not concealed by palatal shelf of maxilla. Dentigerous process of vomers present (each with 3–7 teeth), ovoid in shape, situated posteromedially to the choanas, tongue as wide as long, rounded, its anterior 30% attached to floor of mouth.

Dorsum finely shagreen with small scattered low tubercles and the skin of venter finely areolate. Discoidal fold absent ( Fig. 3 ). Arms slim with respect to the body, fingers with discs, pads defined by circumferential grooves, narrow lateral fringes on all fingers, palmar tubercle U-shaped, thenar tubercle ovoid, subarticular tubercles rounded and prominent, supernumerary tubercles present ( Fig. 4 A). Nuptial pads present, vocal slits and vocal sac absent. Hind limbs slim, tibia length 52% of SVL, heel with a small subconical tubercle, outer-edge of tarsus with low and small tubercles; inner tarsal fold well defined. Toes bear narrowly lateral fringes, subarticular tubercles rounded and prominent, inner metatarsal tubercle ovoid, three times longer that the round outer metatarsal tubercle. Supernumerary plantar tubercles present, tip of toes with discs, toe V larger than III, reaching the subarticular distal tubercle of toe IV ( Fig. 4 B).

Coloration of the holotype. In life ( Fig. 2 ), the anterior region of dorsum copper-brown with tiny dark brown spots; the posterior region dark brown. Head color on eyelid copper-brown with minute scattered black spots. Iris greenish-cream with thin dark brown flecks and a horizontal reddish copper interorbital bar; a white sclera is visible in the inferior and posterior surface of the eye. Supratympanic stripe dark brown, diffuse brown cantal stripe and supralabial chevrons. A yellowish spot at the base of the humeral region. Thighs, groin and posterior region of the flanks with bright-yellow to orange oval spots and blotches surrounded by dark brown to black, forming a reticulated pattern. Venter salmon pink with dark brown flecks in the thoracic region; posterior surfaces of the thighs and groin are dark brown with bright yellowish ovoid spots. Palmar and plantar surfaces red-brown with dark brownish supernumerary tubercles.

In preservative ( Fig. 3 ), dorsum light brown with tiny dark brown spots. Upper eyelid, snout and occipital region grey with small dark flecks. Flanks cream with narrowly dark brown chevrons, the groin dark brown with cream oval spots. Venter pinkish-cream with small black and dark brown spots. Dorsal surfaces of digits pinkishcream with dark spots; dorsal surface of thighs dark brown with pale cream circular marks.

Variation. Morphometrics are presented in Table 1. On one specimen (MZUA.AN.1468), tubercles on the dorsum are more conspicuous, while in a sub-adult (MZUA.AN.0705) the venter is notably areolate. In life, all specimens have well differentiated low tarsal tubercles, although this condition is only partially visible in preservative. Also, one of the paratypes (MZUA.AN.1472) presents two discontinuous copper-brown dorsolateral stripes, and another paratype (MZUA.AN.0705) presents an olive green dorsal coloration with brown marks, brighter yellowish humeral marks and dark-brown labial chevrons ( Fig. 5 ).

Etymology. The specific epithet “ nimbus ” corresponds to the Latin masculine noun for cloudy or dark cloud, and refers to the constant cloudy conditions of the type locality.

Distribution and natural history. Pristimantis nimbus is only known from the type locality, at elevations between 2200–2400 masl. The area is part of the Tinajillas-Rio Gualaceño Ecological Conservation Area, a region of montane cloud forests in the southeastern Andes of Ecuador ( Fig. 1 ). The forest is dominated by tree species of the genera Oreopanax, Weinmannia, Cinchona and Ocotea and the canopy reaches 30 m and is characterized by a high dominance of epiphytes ( Baez et al. 2013). All individuals of Pristimantus nimbus were found at night, perching on leaves and branches between 80 cm to 150 cm above the ground. The analysis of stomach contents rendered a total of 17 prey items of different unidentified species in five orders (Aranae, Coleoptera , Diptera , Hemiptera, Lepidoptera ). 30.9% of prey items could not be determined at the family level but belong to the Coleoptera, Lepidoptera and Aranae. Among the items identified at the family level, most common preys were species in the families Tipulidae (23.5%) and Membracidae (16.6%). Other families preyed upon were Curculionidae (11.6%), Licosidae (5.8%), Tephritidae (5.8%) and Pentatomidae (5.8%). Other species of anurans found in syntopy were Pristimantis cf. altamnis , P. galdi (Jimenez de la Espada, 1870) , P. proserpens ( Lynch 1979) , P. tinajillas ( Urgiles et al. 2014) , P. versicolor (Jiménez de la Espada 1870) , Rhinella margaritifera ( Laurenti 1768) , Noblella sp., and three unidentified species of Pristimantis .

Remarks. The exposed tympanic membrane, expanded digital discs, presence of vomerine teeth, toe V much longer than the III and the absence of a cranial crest are all features that indicate that Pristimantis nimbus fits the definition of the Pristimantis unistrigatus species group (sensu Hedges et al. 2008). However, several studies (e.g., Hoyos et al. 2014; Padial et al. 2014) revealed rampant paraphyly in this group, which was dismantled by Padial et al. (2014). Given the lack of evidence for the monophyly of the Pristimantis unistrigatus group, as well as morphological evidence that would unambiguously place P. nimbus to any of the available monophyletic species groups of Pristimantis , we leave the new species unassigned to group.

Figures

FIGURE 1. Map of Ecuador showing the distribution of Pristimantis nimbus sp. nov. at the Tinajillas-Río Gualaceño Ecological Conservation Area, Morona Santiago, Ecuador.

FIGURE 2. Adult male holotype of Pristimantis nimbus sp. nov. (MZUA. AN. 1475, SVL 24.5 mm) and detail of flash marks on the groin, flanks, hidden surfaces of thighs and arm insertion.

FIGURE 3. Dorsal (A) ventral (B) and lateral (C) views of the preserved male holotype of Pristimantis nimbus sp. nov. (MZUA. AN. 1475; SVL 24.5 mm).

FIGURE 4. Details of the hand (A), foot (B), and dorsal and lateral views of the head (C – D) of the adult male holotype of Pristimantis nimbus sp. nov. (MZUA. AN. 1475).

FIGURE 5. Color variation in specimens of Pristimantis nimbus sp. nov. A) MZUA. AN. 1465 (SVL 25.0 mm), B) MZUA. AN. 1472 (SVL 18.5 mm), C) MZUA. AN. 0705 (SVL 17.7 mm).