Bioacoustics of Pristimantis asimus

Natural history. At Panguana, individuals of this species have been observed being active at night, perching on small trees and bushes within disturbed primary forest. Schlüter (1980) reported males calling from vegetation mainly at 1‒2 m height, with calling activity being most intense at dusk and at dawn, which is confirmed by our own observations. Schlüter (1980) described a vertical calling position with the head down as typical, but we observed calling males in a horizontal position on the upper side of leaves. Individuals of this species have some limited ability to change color, with nocturnal color being characterized by a light brown loreal region, whereas diurnal color is characterized by a dark loreal region and upper lip, turning dark brown to almost black (see Fig. 7 ). The habitat close to the type locality has recently been impacted by illegal gold mining activities, which constitute a potential threat to the anuran fauna of Panguana.

Diagnosis. Pristimantis asimus differs from other species in the Pristimantis danae species group as follows: The new species differs from P. albertus , P. attenboroughi , P. bounides , P. clarae , P. cosnipatae , P. humboldti , P. ornatus , P. pharangobates , P. puipui , P. rhabdolaemus , P. sagittulus , P. similaris , P. stictogaster , and P. toftae , at least by the lack of dorsolateral folds (versus presence). Furthermore, P. attenboroughi , P. bounides , P. humboldti , and P. puipui have stout bodies with relatively shorter legs when compared to P. asimus . Pristimantis attenboroughi and P. puipui lack a tympanum (prominent in the new species), and P. attenboroughi lacks vocal slits in males (present in the new species). Pristimantis clarae additionally differs from the new species by dorsal and ventral color pattern, advertisement call, and smaller adult male size (12.9 – 15.6 versus 27.7–30.6 mm ). As the new species, P. aniptopalmatus lacks dorsolateral folds ( Duellman and Hedges 2005 ) but differs by its smaller adult male size (16.5 ‒ 23.2 versus 27.7‒30.6 mm ), presence of a tubercle on the upper eyelid, and color pattern ( Duellman and Lehr 2009 ). Pristimantis cuneirostris lacks dorsolateral folds but differs from the new species by a long wedge-shaped snout (unique in the P. danae species group; Duellman and Pramuk 1999 ; Duellman and Lehr 2009 ), lack of toe webbing (versus basal webbing present), and posterior surfaces of thighs uniformly brown (versus blackish with yellowish-cream blotches and flecks). Pristimantis scitulus mainly differs from the new species by the presence of a single conical tubercle on upper eyelid (absent), dentigerous processes of vomers absent (present), presence of a conical tubercle on heel (absent), and webbing on toes absent (basal webbing present) ( Duellman 1978 ). Morphologically, P. asimus is most similar or even cryptic to P. danae and P. reichlei . However, as a tendency, nominal P. danae (from Kosñipata valley, Peru ) exhibit a more contrasting dorsal color pattern in life (see, e. g., Duellman and Lehr 2009 : fig. 150) when compared to P. asimus . Moreover, in dorsal view, the snout in P. danae is rounded (versus subacuminate in P. asimus ). From P. reichlei , the new species seems to differ by a very small, round, flat outer metatarsal tubercle, barely recognizable in life and virtually indistinguishable in preservative (versus distinct, ovate, subconical, recognizable in life and in preservative; Fig. 4 ). Moreover, there are slight differences in the dorsal outline of the canthus rostralis, with a relatively smaller portion of the nostrils being visible when viewed from straight above in P. asimus compared to P. reichlei , where nostrils are almost completely visible from above as the canthus rostralis shows a curved indentation around the nostrils (Fig. 5 ). The new species differs from both P. danae and P. reichlei by substantial differentiation in the 16 S gene and differences in the advertisement call (see above). The new species occurs in sympatry with some species of the P. conspicillatus group, which superficially may have a similar appearance. However, these are distinguishable from P. asimus by molecular phylogenetic relationships, differences in advertisement calls, and most of them by different relative finger lengths, i. e., the first finger being longer than the second. However, the sympatric P. iiap has the first and second fingers equal in length but differs from the new species at least by exhibiting distinct dorsolateral folds ( Padial et al. 2016 ).

Vocalization. Advertisement calls of Pristimantis asimus , emitted by the male MUSM 29028, were recorded on 29 November 2008 , at dusk (18: 15 h) at the type locality (ambient temperature not recorded). The calling male was sitting on top of a horizontally oriented leaf at approximately 2.1 m height within the forest. The call consists of a single short pulsatile note, repeated at somewhat irregular intervals (see below). In our recording, 4 to 14 calls were emitted in succession and then interrupted by few seconds of silence. Each call (= note) has a clearly pulsatile structure, although ‘ pulses’ are largely fused and, in most cases, barely countable. However, in some cases, distinct and thus countable energy peaks (4 ‒ 10 / call) are recognizable in the oscillograms of calls. In these calls, the pulse rate varies between 300 and 375 pulses / second. There is further amplitude modulation recognizable within each call, with maximum call energy being present around the center of each call, rapidly decreasing to a lower level, and further fading towards the call’s end. Calls were usually emitted in slow succession but regularly contained sections of more rapidly repeated calls, usually 2–4 calls emitted at shorter intervals, altering the relatively regular pattern of call repetition (see Fig. 8 a ). In other words, call repetition rate may change temporarily from ca. 140 calls / min to ca. 900 calls / min. The character of calls in these rapidly repeated sections did not differ from other calls. It remains unknown whether this increased speed in call succession has a different function (e. g., territorial) or is just part of the ordinary advertisement call. Numerical parameters for 65 analyzed calls of the mentioned male are as follows: call duration (= note duration) 23–47 ms (36.0 ± 7.1 ms); inter-call interval in slow calling sections 305–597 ms (394.6 ± 73.6 ms); inter-call interval in rapid calling sections 26–37 ms (31.8 ± 4.6 ms); dominant frequency 3289–3628 Hz (3518 ± 97 Hz); second frequency peak at around 2000 Hz; prevalent bandwidth 1600–5400 Hz. Schlüter (1980) described the call from the same locality (under the name Eleutherodactylus peruvianus ). The spectrogram and numerical parameters (call duration ca. 40 ms) provided by him agree with our analysis. The call described by Rodríguez (1994) as that of Eleutherodactylus fenestratus from Cocha Cashu, Manu National Park, Madre de Dios , Peru , is also clearly referable to P. asimus . The parameters described by Duellman (2005) for calls of P. fenestratus from Cusco Amazónico clearly differ from those of P. asimus , but the corresponding audiospectrogram and oscillogram are in disagreement with the numerical parameters provided and may possibly correspond to P. asimus . Although difficult to compare according to another terminology used, the call described for E. fenestratus from Manaus, Brazil , by Zimmerman and Bogart (1984) seems to agree with that of P. asimus .

Distribution. As far as known and confirmed by bioacoustic and / or genetic data, P. asimus occurs in lowland rainforests from the southern Departamento Huánuco (Panguana, type locality) and eastern Departamento Ucayali (Breu, Río Yurua) southward across most of the lowlands of southeastern Peru , reaching the border of Machiguenga Communal Reserve (Departamento Cusco ) and Manu National Park (Departamento Madre de Dios ) in the south as well as northernmost Bolivia (Bioceanica, Departamento Pando ) to the east (Fig. 9 ). All known localities are at elevations between 220 and 470 m a. s. l. The new species occurs in syntopy with P. reichlei at least in Alto Purús National Park (La Novia, Departamento Ucayali , Peru ) and probably in other places in southeastern Peru and northern Bolivia . The new species most likely also occurs further east in the Brazilian Amazon, as indicated by the call description of Zimmerman and Bogart (1984) from Manaus, but respective records are in need of clarification (see Discussion).

Definition. A medium-sized species of the Pristimantis danae species group (based on molecular relationships and morphological similarity), with 27.7‒30.6 mm SVL in adult males (n = 7), and 37.9 mm SVL in adult females (n = 1), characterized by: (1) skin on dorsum finely shagreened, lacking enlarged tubercles or warts; throat smooth, venter areolate; discoidal fold inconspicuous; dorsolateral folds absent; upper eyelid lacking tubercles and granules; posterior surfaces of thighs smooth; (2) tympanic membrane and annulus distinct, slightly higher than long, their length less than half of eye diameter; supratympanic fold prominent, curved, slightly covering upper edge of tympanic annulus; (3) head slightly longer than wide; snout subacuminate in dorsal view, bluntly rounded in lateral profile; canthus rostralis straight in dorsal view, slightly rounded in profile; (4) cranial crests absent; (5) dentigerous process of vomers elongate, oblique, situated posteromedial to choanae; (6) males with vocal slits, single subgular vocal sac; indistinct nuptial asperities on dorsal surface of thenar tubercle; (7) hands with slender fingers, first finger slightly shorter or about equal in length to second; subarticular tubercles subconical, prominent; supernumerary tubercles absent; palmar tubercle cordiform; thenar tubercle prominent, elongated; terminal discs of inner two fingers enlarged and round, those of external fingers enlarged, truncate, about twice the width of digit proximal to disc; circumferential grooves conspicuous, ungual flap not indented; narrow lateral fringes on fingers weakly developed; basal webbing between fingers absent; (8) ulnar tubercles absent; (9) tubercles on heel and tarsus absent, tarsal fold present; (10) inner metatarsal tubercle prominent, ovate; outer metatarsal tubercle small, round, flat, barely recognizable in life, virtually absent in preservative; supernumerary tubercles absent; (11) toes long and slender; lateral fringes narrow, weak; basal toe webbing present; toe V reaching beyond distal level of penultimate subarticular tubercle of toe IV; tips of toes rounded to slightly ovate, enlarged; circumferential grooves conspicuous; (12) in life, dorsal coloration light brown, reddish-brown, or tan, usually with dark brown chevrons and flecks on dorsum; dark brown bars on dorsal surfaces of arms and legs; a pair of black spots dorsolaterally in scapular region; black supratympanic stripe; black canthal stripe; belly creamy white; throat with fine dark mottling in males; posterior surfaces of thighs blackish with yellowish-cream spots and flecking; iris bronze, with black reticulation in life; posterior iris periphery cream to turquoise; bones white; (13) advertisement call consisting of a single pulsatile note of 23–47 ms duration and with a dominant frequency of 3289–3628 Hz, repeated at irregular intervals, containing groups of 2–4 calls repeated in faster succession.