Bioacoustics of Pristimantis aureoventris

Distribution and ecology. Pristimantis aureoventris is currently known only from the type locality—the summit of Wei Assipu Tepui (at 2210 m elevation) at the border between Guyana and Brazil—and from near the base of the ultimate cliff of the northern “Prow” of Mount Roraima in Guyana at about 2305 m elevation ( Figs. 1 , 6 , 9 ). According to the GPS, Wei Assipu Tepui reaches a maximum elevation of ca. 2260 m above sea level. Wei Assipu Tepui summit area is about 3 km 2 and is level with a large number of fractures, some of them very deep and impassable without the use of climbing equipment—like the “Sima de los Guácharos”, which is more than 100 m deep (see Carreño et al. 2002 ). The Wei Assipu Tepui summit vegetation is the classic “tepui vegetation”, with large areas of coarse herbs mixed with woody subshrubs on peat soils, some quaking bogs and extensive patches of dwarf forests dominated by Bonnetia roraimae (Theaceae) . The terrestrial bromeliads Brocchinia tatei and B. reducta are especially abundant, as well as Stegolepis guianensis (Rapateaceae) , Orectanthe sceptrum (Xyridaceae) , and Heliamphora nutans (Sarraceniaceae) . Temperature and hygrometry were recorded from the summit of Wei Assipu Tepui between 9–11 November 2009 . A thermo-hygrometer was placed under a small rock in a bare rock area on the summit. The maximum temperature recorded was 29°C (day), the minimum temperature recorded was 13°C (night). Maximum hygrometry recorded was 74% (night), minimum hygrometry was 24% (day). Temperature in the base camp (located under two very large boulders, close to a small forest) was as low as 11°C at night and hygrometry reached 98% during misty nights and mornings. Few rains occurred during our stay in November 2009 , which was mostly very dry. Culminating at 2810 m elevation, Mount Roraima is the highest tepui and second highest point in the Pantepui region (after Pico de la Neblina in the southwest, which reaches about 3000 m elevation). Roraima summit plateau area is about 34 km 2. The plateau is very rocky and its vegetation is very sparse. The reader is referred to Huber (1995a , b ) for description of the vegetation and physical features of Mount Roraima. Mount Roraima and Wei Assipu Tepui are very close to each other (about 2 km airline between summits) and the vegetation at the Roraima site was similar to that on Wei Assipu Tepui, but on an inclined talus slope (see below). Pristimantis aureoventris was found to be mainly nocturnal. Four specimens collected on Wei Assipu Tepui, including the calling male holotype , were found concealed between the basal (brown) leaves of Orectanthe sceptrum (Xyridaceae) ; four other specimens (including the tiny juvenile) were collected between brown leaves at the base of Brocchinia tatei (Bromeliaceae) ; one female was found sitting on bare rock at night; a subadult female was collected at night, sitting on a branch of a small tree about 100 cm above the ground; and one specimen was collected by chance, while escaping from dense vegetation. The individual from near the base of the ultimate cliff of Mount Roraima's northern "Prow" was taken about 10h00 as it jumped across a trail among dense tank bromeliads ( Brocchinia tatei ) and woody subshrubs in what MacInnes (1974) called the El Dorado Swamp. The "swamp" is a patch of tepui summit vegetation dominated by Bonnetia roraimae , Brocchinia tatei , Heliamphora nutans, Utricularia humboldtii, Stegolepis guianensis , Orectanthe sceptrum , and other plants that grow on the inclined, flattish ridge that extends about 1 km north beyond the end of the "Prow" between elevations 1850 and 2200 m ( Fig. 6 ). A completely different forest vegetation dominated by several species of broad-leaved angiosperms including a Schefflera sp., Leguminosae, Clusiaceae , palms, and tree ferns of the genus Cyathea , with understory shrubs of Melastomataceae , grows at the same elevations leading south on the talus slope below the eastern cliff of Mount Roraima all the way to a small saddle connecting Mount Roraima to Wei Assipu. Two nights of collecting in this cliff-base forest did not turn up frogs of any species. Males call at night, hidden in plants among dense vegetation and are usually exceedingly difficult to locate. None of the several males heard calling was exposed. The species is apparently abundant, but specimens are difficult to collect. We are aware of two previous expeditions on the summit of Wei Assipu Tepui during which amphibians were collected (see for instance Villarreal et al . 2002 ), but none of them found Pristimantis aureoventris . Two clutches of eggs were found on the summit of Wei Assipu Tepui, both were in a dead (brown) pitcher at the base of two different Heliamphora nutans plants ( Sarraceniaceae ). Genomic DNA was extracted from one egg of each clutch, and DNA barcoding established conclusively adult and egg conspecificity (0% uncorrected pairwise distance). The first clutch was found on 5 November 2009 in a plant growing at the bottom of a small, very humid crevice ( ca. 300 cm deep) and contained five eggs measuring 5.25–5.62 mm . The second clutch was found on 7 November 2009 , at the edge of another small, very humid crevice ( ca. 600 cm deep) and contained four eggs measuring 5.53–6.10 mm ( Fig. 9 ).

Description of the holotype . An adult male 20.4 mm SVL ( Fig. 2 ) in very good condition of preservation, except a few small scars on back and upper arms. Head slightly longer than wide (HW 90.4% of HL), wider than body, HW 39.9% of SVL, cranial crests absent. Snout rounded in dorsal view, slightly sloping in profile; canthus rostralis nearly straight, round, loreal region slightly concave, sloping outward to lip; nares slightly protuberant, directed posterolaterally. Upper eyelid width narrower than IO; upper eyelid slightly granular with two barely discernible enlarged tubercles on each eyelid (better visible in life). Tympanum distinct, but not conspicuous, slightly obscured posteriorly, vertically oval, TYM 29% of EL, separated from eye by about half its length; supratympanic fold originating at corner of eye, failing to reach shoulder, slightly arched; small postrictal tubercles evident. Choanae small, oval, slightly kidney-shaped, not concealed by palatal shelf of maxillary arch; dentigerous processes of vomers slightly smaller than choanae, oblique, V-shaped, posterior and medial to choanae, each bearing 3 to 4 teeth. Tongue much longer than wide, rounded posteriorly, posterior 2/3 free. Vocal slits absent, shallow subgular vocal sac present, seemingly not very distensible. Dorsal skin shagreened, almost smooth on head; middorsal raphe faint; no scapular folds or ridges visible; dorsal surfaces of limbs shagreened; flanks granular. Throat smooth; venter areolate (coarsely granular); posteroventral thigh and cloacal region areolate; weak discoidal fold anterior to groin; ulnar tubercles low, inconspicuous, not forming a distinct line in preservative, but more visible in life with three of them more prominent, forming a row. Finger I 85 % of II; relative length of adpressed fingers III> IV> II> I; adpressed Finger I failing to reach proximal edge of subdigital pad of Finger II; broad pre- and postaxial lateral fringes on fingers; presence of two whitish non-spinous nuptial pads, one adjacent to thenar tubercle and having about the same size, the other on the posterodorsal side of the thumb, having about the same size as the subarticular tubercle on Finger I. Finger discs expanded, with wide digital pads, broader than long, slightly rounded; distal median edge rounded. Palmar tubercle large, deeply bifid, V-shaped; thenar tubercle large, ovoid; subarticular tubercles large, round; supernumerary tubercles present, relatively large and protuberant ( Fig. 3 ). Hind limbs relatively long; heels overlap when held at right angles to sagittal plane; TIL 55.7% SVL; FL 45.8% SVL. Relative length of adpressed toes IV> V> III> II> I; tip of Toe V extends to distal edge of ultimate subarticular tubercle of Toe IV, tip of III to the distal edge of the penultimate subarticular tubercle of IV. Toe discs as wide or narrower than finger discs, WFD/WTD = 1.11, with wide digital pads. Toes with broad pre- and postaxial lateral fringe, except on Toe I where fringes are barely visible; webbing basal between Toes IV-V. Inner metatarsal tubercle elongate, oval, about twice the size of the round outer metatarsal tubercle; supernumerary plantar tubercles low and round; subarticular tubercles large and protuberant. Calcar tubercles indistinct. Tarsal tubercles low, inconspicuous, not forming a distinct line; inner tarsal fold not visible ( Fig. 3 ). Measurements of the Holotype (mm). SVL 20.4; HL 9.0; HW 8.2; SL 3.5; EN 2.3; IN 1.8; EL 3.2; IO 2.5, TYM 0.9; HAND I 3.6; HAND II 4.2; HAND III 5.8; HAND IV 4.7; WFD 1.1; FL 9.4; WTD 1.0; TIL 11.4. Colour of the Holotype in life. Dorsal ground colour dark brown with two broad light brown longitudinal stripes mottled with dark brown and finely edged by a cream line, extending from tip of snout to vent. Flanks dark brown with ill-defined light brown oblique bands; limbs adorned with similarly coloured ill-defined cross-bands. Arms and legs have a reddish tint. Broad dark brown postocular stripe across upper and posterior parts of tympanum, not contacting eye and failing to reach shoulder; broad dark brown canthal stripe; ill-defined dark brown labial bars from eye to upper lip. Posterior and anterior surfaces of thighs reddish brown, slightly mottled with golden. Throat, chest, and upper belly golden yellow with reddish brown mottling, lower belly and under surfaces of limbs reddish brown; internal organs not visible through the skin. Palms and soles dark brown. Iris greenish bronze, with fine black venation and a median horizontal reddish streak ( Fig. 2 ). Colour of the Holotype in preservative. After 14 months in preservative, patterns and colours faded, but remain roughly the same. The golden ventral colour and the light brown stripes and bands became greyish. Arms and legs still have a slightly reddish tint ( Fig. 2 ). Variation. See Table 1 for measurements, and Figs. 4–6 for intrapopulational variation. Character SVL Males Wei Assipu Tepui (n=7) 21.6 ± 0.8 (20.4–22.7) Females Wei Assipu Tepui (n=3) 26.8 (24.0–29.0) Subadult female Wei Assipu Tepui (n=1) 17.7 Male Mount Roraima (n=1) 19.6 HL 9.2 ± 0.3 (8.6–9.6) 11.6 (10.7–12.2) 7.4 8.4 HW SL 8.5 ± 0.3 (7.9–8.8) 3.8 ± 0.2 (3.5–4.1) 10.4 (9.7–11.2) 4.5 (4.5–4.6) 6.8 3.1 8.3 3.8 EN 2.5 ± 0.2 (2.2–2.6) 3.1 (2.9–3.3) 2.1 2.4 IN EL 2.0 ± 0.1 (1.8–2.2) 3.1 ± 0.2 (2.9–3.3) 2.2 3.3 (3.1–3.5) 1.8 2.1 1.9 3.1 IO 2.6 ± 0.2 (2.3–2.9) 3.2 (3.1–3.3) 2.0 2.5 TYM HAND I HAND II 1.1 ± 0.1 (0.9–1.3) 3.7 ± 0.2 (3.4–4.0) 4.4 ± 0.2 (4.2–4.8) 1.4 4.9 (4.4–5.4) 5.6 (5.2–6.0) 1.0 3.0 3.4 0.8 3.3 3.8 HAND III HAND IV 6.1 ± 0.2 (5.8–6.3) 4.9 ± 0.2 (4.6–5.2) 8.0 (7.0–8.1) 6.1 (5.8–6.4) 4.7 3.8 5.1 4.1 WFD 1.1 ± 0.1 (1.0–1.3) 1.3 (1.2–1.4) 0.7 1.0 FL WTD TIL 9.4 ± 0.3 (9.0–9.6) 1.1 ± 0.1 (1.0–1.2) 11.7 ± 0.2 (11.4–12.1) 11.6 (10.9–12.0) 1.4 (1.3–1.6) 14.9 (14.8–15.5) 7.4 0.6 9.5 8.1 1.0 10.5 The most striking variation occurs in colour and pattern, which are very variable among living individuals ( Fig. 4 ). The holotype is the only specimen having a striped dorsal pattern. Among the other specimens available, the dorsal colouration in life ranges from light golden brown ( e.g. IRSNB 15823, adult male) to dark brown ( e.g. IRSNB 15827, adult male), sometimes with a W-shaped marking on scapula ( e.g. IRSNB 15820 and IRSNB 15643, adult males, and IRSNB 4154, subadult female). One male (IRSNB 15825) has a dark brown dorsum with broad light greyish brown bands on flanks; two individuals (IRSNB 4153, adult female, and IRSNB 15826, adult male) have a brownish dorsum with ill-defined dark brown dorsolateral bands. The ill-defined light brown oblique bands on flanks and the similarly coloured ill-defined cross-bands on legs may be absent ( e.g. IRSNB 15820, adult male). A faint dark interorbital bar is usually visible (absent in the holotype ), this bar being conspicuous in IRSNB 4154 (subadult female). In three individuals (IRSNB 4154, subadult female, IRSNB 15824 adult male, IRSNB 15825, adult male) the snout is paler than body (tan) with some dark markings (a black inverted triangle in IRSNB 4154). A dark brown to black postocular stripe across upper and posterior parts of tympanum is present in all specimens from Wei Assipu Tepui, that stripe is poorly detectable in the Roraima specimen. Groin is usually black or brown, sometimes with some small golden spots; one male (IRSNB 15827) had a conspicuous reddish orange flashmark on its groin in life ( Fig. 7 ), which became white after preservation. Arms and legs usually have a reddish or orangish tint; IRSNB 15824 (adult male) had the posterior and anterior surfaces of thighs, the tibio-tarsal articulation, and part of the feet including Toes III–IV bright red; IRSNB 15825 (adult male) had the tibio-tarsal articulation distinctly paler (light grey) than the legs (dark brown); IRSNB 4154 (subadult female) had the anterior surface of thighs, the posterior surface of shanks, and part of the feet including Toes III–IV orange, a similar pattern is visible in IRSNB 15826 (adult male), but much less vivid. In other specimens, the posterior and anterior surfaces of thighs are reddish brown to dark brown, slightly mottled with golden. Under surfaces of limbs are reddish brown to dark brown, often heavily spotted with golden. Mottling on venter varies from reddish brown to dark brown, almost black, and is variably extensive; two individuals (IRSNB 15823, adult male from Wei Assipu Tepui, and IRSNB 15643, adult male from Mount Roraima, see Figs. 4 , 6 ) lack mottling on venter. Due to the golden colouration of the venter, internal organs are little (IRSNB 15822, adult female) or not ( holotype and other specimens) visible through the ventral skin in life ( Figs. 2 , 4 ). Iris colouration is variable, some individuals lack the median horizontal reddish streak ( e.g. IRSNB 15822, adult female); IRSNB 15820 (adult male) has a blue-green iris ( Fig. 4 ). In preservative all specimens became darker and variation in colour and pattern is less visible, but is still discernible ( Fig. 5 ). Dorsal skin texture is slightly variable, most individuals having the dorsal skin shagreened to slightly granular. One specimen however (IRSNB 15827, adult male) has small conspicuous conical tubercles on anterior dorsum and legs, as is the case in the tiny ( 7.1 mm SVL) referred juvenile (IRSNB 15637). Few small conical tubercles are also visible on legs of most of the specimens. Small scapular tubercles were visible in seven individuals of both sexes in life (IRSNB 15822–24, IRSNB 15827, IRSNB 15643), but these tubercles are barely seen on the preserved animals and are absent in the holotype . Eyelid tubercles can be conspicuous ( e.g. in IRSNB 15824, adult male) or barely visible ( e.g. in IRSNB 15820, adult male). Number of teeth on dentigerous processes of vomers varies from two to five; they are absent in the very small juvenile (IRSNB 15637). A weak discoidal fold anterior to groin is visible only in the holotype and in two other specimens (IRSNB 15826, adult male, IRSNB 4153, adult female). The tip of Toe V fails to reach the distal edge of the ultimate subarticular tubercle of Toe IV on both sides in one female (IRSNB 4153), and on one side in four individuals of both sexes (IRSNB 15822–24, IRSNB 15643). No obvious sexual dimorphism is noted, except in size (females are larger than males). Other differences among available specimens are considered minor. Advertisement call. The following description is based on a sample of 21 advertisement calls from the male holotype (IRSNB 4152), recorded on the summit of Wei Assipu Tepui ( 05° 13’ 05”N , 060° 42’ 15”W , 2210 m elevation), on 17 November 2009 at 20h00, air temperature 15.0°C. The male was calling concealed between the basal leaves of an Orectanthe sceptrum (Xyridaceae) growing ca. 150 cm above the ground on the wall of a 300-cm deep small crevice. Temporal structure. The advertisement call of Pristimantis aureoventris consists of a soft, single, unpulsed note (perceived by the human ear as a small drop falling in the water). Calls are apparently emitted in bouts of about 20 calls (variation of the number of calls in each bout is unknown). The call rate was 18 calls/min based on a 1-min period. The mean call duration is 0.021 ± 0.002 and varies from 0.017 to 0.023 s. The inter-call interval is rather uniform and has a mean of 3.097 ± 0.275 and a range of 2.730– 3.610 s ( Fig. 8A ). Spectral structure. Three harmonics are apparently developed, with the fundamental frequency dominating (mean: 2295, range: 2180–2430 Hz) ( Fig. 8A ). The third harmonic contains slightly more sound energy than the second. The three harmonics show a feeble “U-shaped” frequency modulation ( Fig. 8A ). Comparisons. Unfortunately, very few detailed descriptions of Pristimantis advertisement calls are available from the highlands of the Pantepui region. Myers and Donnelly (1996) provided analyses of unvouchered calls of different individuals of two highland Pristimantis species (tentatively assigned to P. cantitans and P. pruinatus ) from Cerro Yaví, a massif located ca. 680 km W airline from Wei Assipu Tepui, and Rödder and Jungfer (2008) described the call of P. yuruaniensis from Yuruani Tepui located ca. 19 km airline NW from Wei Assipu Tepui. The call of P. a u re o v e n t r i s mostly differs from the calls described from Cerro Yaví in call duration and fundamental frequency: call duration varies from 0.017 to 0.023 s in P. aureoventris vs. 0.047 to 0.075 s in the type I call (presumably P. cantitans ) and vs. 0.028 to 0.056 s in the type II call (presumably P. pruinatus ) of Myers and Donnelly (1996) ; fundamental frequency varies from 2180–2430 Hz in P. aureoventris vs. 1520–1720 Hz in the type I call and vs. 2440–2660 Hz in the type II call of Myers and Donnelly (1996) . To the human ear, the call of P. yuruaniensis sounds more or less similar to that of P. aureoventris , but higherpitched. Analysis indicates differences in note duration (0.017– 0.023 s in P. aureoventris vs. 0.093– 0.139 s in P. yuruaniensis ), in fundamental frequency (2180–2430 Hz in P. aureoventris vs. 1860–2080 Hz in P. yuruaniensis ), in inter-call interval (2.730– 3.610 s in P. aureoventris vs. 0.504– 1.968 s in P. yuruaniensis ), and in harmonics structure (three harmonics showing a feeble “U-shaped” frequency modulation in P. a u re o v e n t r i s v s. five indistinctly modulated harmonics in P. yuruaniensis ). Additionally, the distribution of sound energy decreases progressively through the higher harmonics in P. yuruaniensis , while in P. aureoventris the third harmonic contains slightly more sound energy than the second (compare Fig. 8A with Fig. 8 B). Some of these variations could be caused by intrinsic parameters ( e.g. size variation, see Duellman & Trueb 1986 ). Apparent similarity between calls of Pantepui Pristimantis species might be interpreted as a plesiomorphic trait.