Allobates pacaas, Melo-Sampaio & Prates & Peloso & Recoder & Dal Vechio & Marques-Souza & Rodrigues, 2020

Melo-Sampaio, Paulo R., Prates, Ivan, Peloso, Pedro L. V., Recoder, Renato, Dal Vechio, Francisco, Marques-Souza, Sergio & Rodrigues, Miguel T., 2020, A new nurse frog from Southwestern Amazonian highlands, with notes on the phylogenetic affinities of Allobates alessandroi (Aromobatidae), Journal of Natural History 54 (1 - 4), pp. 43-62 : 46-54

Allobates pacaas sp. nov.

Figures 2 – 4.

Holotype. MZUSP 158934 (field number MTR 25831 Figures 2 – 4), an adult female from Pico do Tracoá , Parque Nacional dos Pacaás Novos, Campo Novo de Rondônia municipality, state of Rondônia, Brazil (10.84892°S, 63.63312°W; 911 m above sea level), collected by I. Prates, R. Recoder, F. Dal Vechio, S. M. de Souza, M. Teixeira Jr., and M. T. Rodrigues on 21 April 2013.

Paratopotypes. Eight males MNRJ 93128 (field number MTR 25829), MNRJ 93129 (MTR 25839), MZUSP 158935 (MTR 25867), MZUSP 158936 (MTR 25843), MZUSP 158937 (MTR 25868), MZUSP 158938 (MTR 25840), MPEG 42818 (MTR 25837), MPEG 42819 (MTR 25838), and one female UFAC-RB 9470 (MTR 25830), all adults and with the same collection data as the holotype .

Referred specimen. UFAC-RB 6798 , from Parque Nacional Pacaás Novos, Base Candeias (10.79111°S, 63.63030°W; 410 m above sea level), collected by K . D . Zaqueo on 17 July 2014.

Diagnosis. The new species is assigned to Allobates based on morphological similarity and on results of a phylogenetic analysis of DNA sequence data. The species is diagnosed from its congeners by the following combination of characteristics: (i) snout rounded in lateral and dorsal views; (ii) a small-sized species, mean SVL of males 13.9 mm (range 12.8 – 15.2 mm), mean SVL of females 15.6 mm (range 14.7 – 16.6 mm); (iii) dorsal surface of snout light brown, same colour extending posteriorly until eye level; dorsum tan brown in life with an hourglass pattern and scattered golden flecks; (iv) skin texture smooth throughout the body; (v) lateral dark brown band with well-delimited upper edge and ill- defined lower edges; (vi) abdominal surface cream with scattered melanophores; melanophores more concentrated around lips and ventral surface of thigh; (vii) dorsal surface of legs with conspicuous dark brown transversal stripes; (viii) dark throat-collar absent; (ix) iris metallic gold to coppery brown without vermiculation; (x) vocal sac distinct, single, subgular; (xi) maxillary teeth present; (xii) Finger III not swollen in males; (xiii) presence of two subarticular tubercles in Finger IV; (xiv) rudimentary basal webbing present between Toes III and IV; (xv) slightly expanded discs on fingers and toes; (xvi) fringes absent on finger and toes.

Description of the holotype. An adult female with SVL 16.6 mm, HL 4.9 mm, HW 4.2 mm, IOD 3.0 mm, ET 2.2 mm, IND 1.5 mm, ED 1.7 mm, TD 0.8 mm, FAL 3.4 mm, UAL 4.0 mm, HANDIII 4.1 mm, WDFIII 0.5 mm, TL 7.6 mm, FL 7.4 mm, WDTIV 0.5 mm. Head slightly longer than wide, HL 115.6% of HW, HW 25.5% of SVL, HL 29.4% of SVL. Snout rounded to nearly truncate in dorsal and lateral views ( Figures 2 – 4). ETD 44.9% of HL, IND 36.2% of HW, ETD 79.5% of ED. Nares opening laterally. Tympanum behind and lower than the eye, close to the angle of jaws, covered superiorly by a supratympanic fold; lower part of tympanic annulus visible; TD 44.8% of ED. Tongue nearly twice as long as wide, attached anteriorly, rounded posteriorly; median lingual process absent. Skin texture smooth throughout the body. Cloacal tubercles absent.

Forearm and upper arm nearly identical in thickness; FAL 117.6% of UAL. Finger III length 24.8% of SVL; tip of Finger IV reaching distal subarticular tubercle of Finger III when fingers are adpressed; Finger II reaching the distal subarticular tubercle of Finger III; relative length of fingers III>I> II>IV; Finger III not swollen; webbing and lateral fringes absent on fingers. Palmar tubercle nearly ovoid; thenar tubercle present, ovoid; a single subarticular tubercle present on Finger I, and II, two subarticular tubercles on Finger III and IV. Discs of Fingers I, II, III and IV slightly expanded, all with distinct dorsal paired scutes; width of the disc on Finger III 0.47 mm.

Tibia length 45.9% of SVL. Relative length of toes IV>III>V> II>I; rudimentary basal webbing present between Toes III – IV; webbing absent between Toes II – III; fringes absent on all toes. Tip of Toe I barely reaching proximal subarticular tubercle of Toe II when toes are appressed; tip of Toe III reaching medial tubercle of Toe IV. Inner metatarsal tubercle ovoid and outer metatarsal tubercle rounded. Metatarsal fold present, weakly developed; tarsal keel present, conspicuous and curved, tubercle-like. A single subarticular tubercle present on Toe I; two subarticular tubercles present on Toes II, III and V; three subarticular tubercles present on Toe IV.

Colour of the holotype in preservative. Dorsal surface of body generally dark brown, except on the snout region (anterior corner of the eyes to the tip of snout) and for the two dorsolateral stripes, where colour is paler (light brown; golden) delimiting an hourglass dorsal pattern ( Figure 2 (a)). Scattered golden flecks are present on the posterior surface of the dorsum. Dorsolateral stripes are present from the posterior corner of the eye to the groin, becoming faint posteriorly; weakly defined on the inner margins (view under magnification). Lateral surface of the body characterised by a solid, wide, dark brown stripe, extending from the tip of the snout to the groin; ventral margin ill- defined.

Arms and hands pale brown in dorsal view; tip of the fingers light brown; paired scutes on finger discs brown. Dorsal surface of thighs with intercalating light and dark brown stripes of similar width; dorsal surface of tibias with intercalating brown and dark brown stripes of similar width; dorsal surface of feet brown.

Throat, gular, and anterior pectoral regions pale, with a conspicuous presence of melanophores on the marginal areas of the throat, evenly spaced elsewhere. Pectoral region, abdomen and ventral surface of thigh insertion pale cream; scattered and evenly spaced melanophores on pectoral and abdominal region; heavily pigmented (high concentration of melanophores) on ventral surface of thigh and knees; ventral surface of upper arm similar to pectoral and abdominal region, forearm and hand completely pigmented (brown). Ventral surface of legs and feet completely pigmented (brown). Tips of fingers and toes light brown.

Arms cream to pale brown in dorsal view, melanophores concentrated in small and regular light brown blotches on posterior surfaces of upper arm, forearm and hand. Tip of fingers light brown. Paired scutes on finger discs cream. Upper arm cream in ventral view. Forearm and hand tan brown in ventral view.

Colour variation in preserved specimens. Trunk dorsal colour pattern varies considerably in the type series. UFAC-RB 9470 and MZUSP 158935 are most similar to holotype . In MPEG 42818, MZUSP 158936, and MZUSP 158937, the inner margins of the dorsolateral

stripes are rugged, forming an hourglass-shaped pattern. On MPEG 42819 and MNRJ 93129, the inner margins of the dorsolateral stripes are irregular with projections inwards, forming a reticulated pattern. The lateral stripes are uniformly brown in the MZUSP 158935, MZUSP 158938 and UFAC-RB 9470. Oblique lateral stripes are present in MPEG 42818, MZUSP 158936 and MZUSP 158937; golden mottling over the stripes is present in MPEG 42819 and MNRJ 93129.

Colour of adults in life. Head copper to pinkish with small dark brown spots ( Figure 5). Copper to tan-brown dorsum with a dark brown hourglass surrounded by narrow golden line (incomplete in darker specimens). Lateral bands dark brown. Pale ventrolateral stripes interrupted at the level of arm insertion, running faded from axilla to groin. Forelimbs orange in dorsal surface. Hindlimbs copper to tan brown with dark brown transversal stripes. Ventral surface of female metallic cream; males with violet throat and metallic cream chest and belly.

Comparisons. We compare the new species to the other species inferred as members of the same major clade within Allobates ( Figure 1) and with sympatric or geographically close species from southwestern Amazonia.

The presence of two subarticular tubercles on Finger IV distinguishes A. pacaas from all other Amazonian Allobates species except Allobates hodli ( Simões, Lima and Farias, 2010).

Regarding its closest relatives, A. pacaas is distinguished from A. masniger , A. nidicola , and A. nunciatus in having an hourglass-shaped, dark brown, pattern on dorsum and orange arms (uniform brown dorsum and pale brown arms in A. masniger , A. nidicola , and A. nunciatus ). Allobates pacaas further differs from A. masniger and A. nidicola in having a light white belly (dark belly in A. masniger and A. nidicola ). Allobates pacaas differs from A. flaviventris and A. magnussoni by the absence of a golden-yellow belly (present in A. flaviventris and A. magnussoni ).

Relative to other southwestern Amazonian species, Allobates pacaas differs from Allobates brunneus ( Cope, 1887) by having a smaller size (maximum SVL <16.6 mm in females), dorsal skin smooth, and metallic white venter (maximum SVL 19.8 in females, dorsal skin granular, and lemon-yellow venter in A. bruuneus ). Allobates pacaas differs from Allobates gasconi ( Morales, 2002) by having the Finger III not swollen and dark throat in males in life (swollen Finger III and white throat in life in A. gasconi ). Allobates pacaas differs from Allobates conspicuus ( Morales, 2002) , A. grillisimilis ( Simões, Sturaro, Peloso and Lima, 2013b), and A. subfolionidificans ( Lima, Sanchez and Souza, 2007) by having an hourglass pattern on the dorsum (uniform dorsum with dorsolateral and ventrolateral stripes in A. conspicuus and A. grillisimilis ; without ventrolateral stripes in A. subfolionidificans ). Allobates pacaas further differs from A. conspicuus and A. subfolionidificans by having a dark throat in live male specimens (throat white to translucent in males of A. conspicuus and A. subfolionidificans ). Allobates pacaas differs from A. tapajos by having a violet throat in live male specimens (golden yellow in A. tapajos ). Allobates pacaas differs from A. tinae Melo-Sampaio, Oliveira, and Prates, 2018 by having dark brown transversal stripes on thighs and dark throat in males (absent transversal stripes on thighs and golden-yellow throat in males of A. tinae ). Allobates pacaas differs from Allobates fuscellus ( Morales, 2002) and A. trilineatus ( Boulenger, 1883) by the absence of swelling on Finger III and presence of a dorsal hourglass pattern (swollen Finger III and dorsum uniform with dorsolateral stripes in A. fuscellus and A. trilineatus ). Lastly, A. pacaas differs from Allobates femoralis ( Boulenger, 1883) and A. hodli by the absence of red, orange or yellow marks on the dorsal surface of thighs and axilla (red, orange or yellow flash marks on thighs and axilla in A. femoralis and A. hodli ).

Etymology. Allobates pacaas is named in recognition of an important natural refuge in the Brazilian state of Rondônia. The region has experienced intense deforestation since the 1960s with large-scale loss of biodiversity ( Fearnside 1987). The specific epithet is a noun in apposition to the genus.

Distribution and natural history. The Parque Nacional de Pacaás Novos is situated in the western part of the state of Rondônia and covers an area of about 765,000 ha. The

national park widely overlaps with the Terra Indígena (indigenous territory) Uru-Eu-Wau- Wau ( Figure 5 (a)). Major rivers draining the area are the Madeira, Mamoré, Guaporé, Machado and Candeias. Elevation varies from about 200 up to 1,230 m on the Pico do Tracoá, in a rare instance of mountains in the western part of the Amazon Basin east of the Andes. There is an altitudinal gradient of habitat types in the park; most of the lower areas are covered by tropical rainforest, while above 700 m, forests progressively dwindle and give space to open Cerrado-like savannahs with rocky fields and scattered vegetation.

The type series of A.pacaas was collected at two nearby sites on top of the Pico do Tracoá, at an approximate elevation of 900 m ( Figure 5 (b-c)) (IBGE 2012). The first site (10.84892°S, 63.63312°W) is characterised by rocky outcrops and low vegetation adjacent to a stream (the Rio Pacaás Novos) with clear waters and waterfalls, where some specimens were found hiding in clusters of tall grasses on river banks. The second site (10.84361°S, 63.62726°W) is a dense and short gallery forest adjacent to the same stream, where the species was found on the leaf litter. All specimens were found active during the day. Allobates pacaas was not detected in two well-sampled lowland rainforest sites, where A. flaviventris was found ( Figure 5 (a)). We did not witness any reproductive or call activity, potentially as a result of the lack of rains during the sampling period.