Allobates vicinus Fouquet & Ferrão & Jairam 2023, sp. nov.

Allobates vicinus sp. nov.

Allobates granti Fouquet et al. 2007; 2012; Vacher et al. 2020; Grant et al. 2017

Allobates cf. granti Fouquet et al. 2015a

Allobates aff. granti Réjaud et al. 2020

Holotype. MNHN-RA-2022.0079 (field n° AF3771), an adult male from Voltzberg, Suriname (4.68169 N 56.18568 W, 100 m asl) collected by A. Fouquet and R. Jairam on 25/01/2016 (Fig. 5).

Paratopotypes. two adults: NZCSA1181 (field n° AF3777) a male and MNHN-RA-2022.0080 (field n° AF3805), a female collected with the holotype.

Paratypes. Twelve adults: MNHN-RA-2022.0070–74 (field n° AF2476; AF2479; AF2510; AF2513; AF2515), five males and MNHN-RA-2022.0067–68 (field n° AF2416; AF2421; AF2474), three females from Nassau, Suriname (4.80262 N 54.61502 W, 580 m asl) collected by A. Fouquet and R. Jairam on 20/12/2014; MNHN-RA-2022.0075–78 (field n° AF3428–9; AF3431; AF3436), four males from Bakhuis, Suriname (4.70646 N 56.77943 W, 340 m asl) collected by A. Fouquet and R. Jairam on 05/01/2015.

Etymology. The specific epithet “vicinus” is a latin word that means “neighbor”, referring to the two sister species A. granti in French Guiana and A. vicinus sp. nov. in Suriname facing each other on each side of the Maroni River.

Generic placement. The new species is assigned unambiguously to the genus Allobates because the tip of finger IV does not reach the distal subarticular tubercle of finger III, toe IV with basal webbing and lateral fringe on its preaxial side, pale paracloacal marks (characters 5, 43 and 50 of Grant et al. 2017, respectively) and its phylogenetic relationship as assessed by molecular data.

Definition. A small species of cryptically-colored Allobates. (1) Mean SVL of males 15.5 mm (range 14.6–16.5 mm); mean SVL of females 16.6 mm (range 16.0– 17.1 mm); (2) In life, dorsal surface light brown with diffuse dark brown irregular blotches often forming an hourglass pattern and sometimes only scattered from interorbital to urostyle region; background color of dorsal surfaces of legs light brown to gray; diffuse, transverse dark brown bands present across dorsal surfaces of thigh (on its proximal region), irregular bands on shank (at mid-level), tarsus and foot (at mid-level); posterior surface of thigh and groin dark brown; (3) skin texture of dorsum granular, with numerous and large tubercles scattered throughout dorsum, more abundant on the posterior half and legs; (4) lateral dark brown band with sharp upper and lower edge, as large as the posterior edge of the eye; (5) pale dorsolateral stripe poorly delimited dorsally by the hourglass pattern and sharply delimited ventrally by the dark brown colouration of the flanks; (6) oblique lateral stripe inconspicuous not reaching midbody length reduced to inguinal region of the lateral dark brown band; (7) pale ventrolateral stripe present only in live specimens, extending from the inguinal region to the snout, sometimes interrupted and irregular forming a marbled pattern extending ventrally; (8) white or cream comma-shape paracloacal mark; (9) throat and chest of males cream in preserved specimens, translucent in life, with uniformly distributed melanophores from the chin to the anterior half of the abdomen; (10) abdominal surfaces white centrally, yellow towards the flanks and ventral surface of legs in live males; (11) throat, chest and abdomen uniformly white in preserved specimens and bright yellow in live females, without any melanophores; (12) dark throat collar absent; (13) iris metallic copper, without a pupil ring; (14) median lingual process absent; (15) vocal sac distinct, subgular; (16) maxillary teeth present; (17) third phalanx of Finger III slightly swollen preaxially in males; (18) distal tubercle absent on Finger IV; (19) tip of Finger IV not reaching the distal subarticular tubercle of Finger III; (20) tip of Finger II reaching the distal edge of distal subarticular tubercle of Finger III; (21) terminal discs weakly expanded; (22) rudimentary basal webbing present between Toes III and IV; (23) fringes on toes inconspicuous; (24) Toe I very short, its tip reaching the base of the subarticular tubercle on Toe II; (25) mature oocytes pigmented; (26) diurnal habits, males calling in daytime; (27) advertisement calls characterized by the continuous emission of note pairs; notes with ascending frequency modulation with dominant frequencies between 5,422 –5,785 Hz for the first note and 5,586 –6,020 Hz for the second, split by regular silent intervals of approximately 233–374 ms between calls.

Morphological comparisons with other Allobates. The character states of compared species are shown in parenthesis. Allobates vicinus differs from its closest relative A. granti (Fig. 6) by (1) its brown legs (gray-blueish); (2) its dorsum with numerous and large tubercle (finely granular); (3) its hourglass darker pattern on a light brown coloured back (brick or reddish-brown, rarely with an hourglass pattern); (4) by its dark brown lateral band, in life and preservative (uniformly black, exceptionally dark brown); (5) by its call consisting of two notes with distinct maximum dominant frequencies DMxF1–2: 190–347 Hz (very similar values between the two notes DMxF1–2: -44–90 Hz in A. granti) (Fig. 3D) and longer intervals between calls SC: 233–374 ms (151–202 ms in A. granti) (Fig. 4).

See below the comparison with the other species of Allobates occurring in the Guiana region.

According to the literature Allobates vicinus differs from A. sumtuosus (Morales 2002; Kok & Ernst 2007; Simıes et al. 2013) by (1) its throat uniformly covered with melanophores in males (melanophores restricted to tip and sides of chin in A. sumtuosus males); (2) the presence of transverse dark brown marks on thigh, shank and tarsus (absent or brown irregular spots); (3) its call consisting of pairs of notes (3.9– 5.9 s long trills of 23–35 single notes) with dominant frequency of 5,422 –6,020 Hz (vs. 6,172 –6,480 Hz).

According to the literature Allobates vicinus differs from A. amissibilis Kok, H ̂lting, and Ernst, 2013 by (1) its belly coloration in life clearly sexually dimorphic being white in male, yellow in females, (cream to yellow in both sexes); (2) its oblique lateral stripe inconspicuous, not reaching midbody length (diffuse broad area extending from groin to about midbody length); (3) its calls consisting of pairs of notes (0.03– 7.98 s long series of 1–19 single notes).

Description of the holotype. An adult male 15.5 mm SVL (Fig. 5; Table 1) in good condition, with a few superficial scars on dorsum and a large incision in the abdomen for tissue sample; body slender; head as wide as long (HL/ HW= 1.0); head length 33.4 % of SVL; snout broadly subacuminate in dorsal view, acutely rounded in lateral view, extending past lower jaw. Nares located laterally, opening posterolaterally; canthus rostralis concave, loreal region slightly concave, slightly flaring at upper lip; internarial distance 40.1 % of head width (IN/HW); eye-naris distance 29.8 % of head length (EN/HL); 77.0 % of eye length (EN/ED). Tympanum subcircular, directed posterolaterally, 45.0 % of eye length (TD/ED); supratympanic fold absent, supratympanic area slightly concave; tympanic annulus visible anteroventrally, posterodorsal aspect of tympanum barely visible. Tongue attached anteriorly, broadly rounded posteriorly, longer than wide, median lingual process absent. Choanae very small, subcircular, lateral. Vocal slits long, lateral. Very small teeth present on maxillary and premaxillary, dentigerous process of vomers absent. Cloacal tubercles absent; vent at level of upper thighs, a small anal flap above it.

Skin granular on dorsum, granules weakest on head, with scattered larger granules becoming denser posteriorly, more easily visible in life; one distinctly enlarged tubercle on each eyelid; belly smooth.

Forelimb slender, skin smooth; metacarpal ridge absent; ulnar fold absent; hand length 22.2 % of SVL; Finger I longer than II when fingers adpressed; fingers unwebbed, preaxial edge of Finger III slightly swollen; tip of Finger IV not reaching distal subarticular tubercle on Finger III when fingers adpressed; terminal discs weakly expanded, slightly wider than long; width of disc on Finger III 0.38 mm; discs with distinct dorsal scutes. Relative lengths of adpressed fingers III>I> II> IV; palmar tubercle large, ovoid, 0.65 mm in its largest diameter, 18.9 % of hand length, periphery pigmented; thenar tubercle conspicuous but not protuberant, ovoid, anterior periphery pigmented, about a quarter the size of the palmar tubercle and narrowly separated from it. One subarticular tubercle on Fingers I, II, and IV; two subarticular tubercles on Finger III; subarticular tubercles on Finger I and II subequal and largest, distal tubercle on Finger III smallest (Fig. 5).

Hindlimb robust, skin granular; thigh length 42.9 % of SVL; tibia length 45.9 % of SVL; heels overlapping when hindlimbs are flexed at right angles to sagittal plane of body; foot length 40.2 % of SVL; relative length of adpressed toes IV> III> V> II> I; Toe I very short, its tip reaching the base of the subarticular tubercle on Toe II when toes are adpressed; discs on Toes II, III, IV, and V larger than width of distal phalanges; disc on Toe I equal to width of distal phalanx. Width of disc on Toe IV 0.60 mm; rudimentary webbing present only between Toes III–IV, webbing not pigmented; lateral fringes inconspicuous. Inner metatarsal tubercle oval, 0.40 mm in length, distal portion pigmented, outer metatarsal tubercle round, projecting, 0.32 mm in diameter. Three subarticular tubercles on Toe IV, two subarticular tubercles on Toes III and V, and one on Toes I and II. Subarticular tubercles on Toes I and II largest; distal and basal subarticular tubercles on Toe IV smallest. Metatarsal fold absent. Tarsal keel well defined, short, tubercle like, directed transversely across tarsus, located 0.90 mm from proximal edge of inner metatarsal tubercle, not extending from it (Fig. 5).

Color of holotype in life. Color in life of the holotype is shown in Fig. 5. Dorsal coloration is brown with a dark brown diffuse hourglass pattern from the scapular region to the urostyle; laterally a wide dark brown (almost black) band from tip of snout to around the body and above the vent, as wide as the eye at the level of its posterior edge; inconspicuous dorsolateral stripe above this band. The upper surface of tympanum is black, the lower surface white. The oblique lateral stripe embedded in the dark brown band consists of a diffuse lighter area extending from the groin to about one-third of the distance to the arm insertion. Flanks are creamish white below the lateral dark brown band forming a ventrolateral stripe extending ventrally along flanks. Upper lip is creamish white. Throat is gray entirely covered with scattered melanophores. Belly is immaculate creamish white anteriorly with tiny scattered melanophores and yellowish posteriorly without melanophores. Forelimbs are light reddish with a dark brown line on the posterior surface of forearms from elbow to wrist. A black blotch is present on the dorsal side of wrists. Upper surfaces of thighs and shanks are dark brown with inconspicuous black bands and blotches. A pale comma-shape paracloacal mark is present. Digits are dark gray with a few white dots. Fingers are dark gray with a few small white shaped dots. The iris is copper.

Color of the holotype in preservative. After six years in preservative (70% ethanol), the colors of the specimen have faded. The dorsum is light brown; the lateral band is dark brown and the diffuse oblique lateral stripe is barely distinguishable. Flanks, belly, and upper lips are immaculate white. Throat is white; the melanophores are visible. Upper surface of thighs is brown with dark brown blotch or dark brown band. The pale paracloacal mark is still visible. Forelimbs are white. Fingers and digits are light brown.

Variation in the type series. Apart from sexual dimorphism and dichromatism (males are slightly smaller than females and the ventral surface of females in life is bright yellow and without melanophores), most of the specimens have a clear dark brown dorsal hourglass pattern, although in a few specimens the pattern is only diffused (holotype) or reduced to irregular blotches (MNHN-RA-2022.0068; Fig 6). The dorsal surface of legs varies in coloration from dark grey to light brown with more or less conspicuous dark brown bands and blotches. The ventrolateral stripe is interrupted in some individuals (MNHN-RA-2022.0070; Fig 6) and does not extend ventrally in most females (MNHN-RA-2022.0068; Fig 6). Ventral surface is posteriorly immaculate white to yellow.

Advertisement call. The call consists of pairs of high pitched notes and is emitted regularly (without clear clusters) every 295 ms (233–374 ms) and sounds like a cricket chirp. The two notes within a call are spaced by 34 ms (30–39 ms) with the first note being shorter 24 ms (13–31 ms) than the second one 34 ms (27–43 ms). These notes have an upward frequency modulation, i.e. the first note varies from 5,422 –5,785 Hz as dominant frequency (DF1) and second note varies from 5,586 –6,020 Hz (DF2) but differs more clearly in maximum frequencies (190– 247 Hz) (DMxF1–2). The maximum frequency of the first note is lower (5,635 –6,035 Hz) than of the second note (5,869 –6,275 Hz) (Fig. 3a).

Natural history and distribution. It is a diurnal and terrestrial species inhabiting the leaf litter of mature forest on moderate hills and massifs. It is particularly abundant along the slopes of swampy streams where the males transport the tadpoles to complete their development. Allobates vicinus probably has a breeding ecology similar to its sister species A. granti, where the tadpoles are deposited in small collections of water formed along swampy streams and at the base of trees or by the stems of fallen palms. This species can also be observed far from any permanent water body. Males are territorial and defend territories of a few square meters throughout the rainy season. When an intruder approaches, the occupant emits a vocalization distinct from the usual advertisement call. The calling activity is concentrated in the morning between 7 and 10 am and at the end of the afternoon between 4 and 7 pm. One male can keep several clutches during the same period and could be replaced by the female for guarding of the eggs as well as transport to a water body.

The species described herein is known from seven localities in Suriname; three from which type material is included: Voltzberg, Nassau, and Bakhuis mountains; and four more from molecular data: Lely mountain, Brownsberg, Raleighvallen and the Gros Rosebel area. The range of Allobates vicinus probably extends throughout the forested area of Suriname. However, it reaches its eastern boundaries along the Maroni River. Southward, A. vicinus may enter in contact with the third related lineage remaining unnamed (A. aff. granti 2) and with A. sumtuosus. A similar pattern of distribution and degree of molecular divergence between A. granti and A. vicinus was recently described in Pristimantis grandoculis from Suriname and its sister undescribed species (P. sp. “Guianas” East) from French Guiana, although the lack of phenotypic divergence advocates to consider the French Guiana populations as conspecific (Fouquet et al. 2022). There are also many other examples of species that similarly display pronounced genetic divergence across the Maroni River (Fouquet et al. 2012).