Bioacoustics of Scarthyla vigilans

Natural History: Scarthyla vigilans is a small, inconspicuous species, despite being very abundant. It inhabits marshes, channels, ditches, slow-movement rivers and streams, lakes and even brackish coastal areas of the Maracaibo lake. Calling males are more often seen, as they call from high in the grasses or leafs on floating plants (water hyacinths, water lettuces, etc.), and jump quickly to escape. Females are larger and stay at lower stages on the same plants. S. vigilans , like S. goinorum , can escape jumping to the water and skittering on the surface (Duellman and De Sá 1988 ; Duellman 2005 ). One ovigerous female at San Vicente , estado Apure, laid 95 bicolored ova. During dry season they usually remain undetectable (not calling at all), but the first author, while searching for anacondas ( Eunectes murinus ) on March 2006 , at 1300 h, in a dry pond with still green water hyacinths, observed uncountable S. vigilans jumping and escaping through all the pond. In La Acequia, Barinas, the species is micro-sympatric with Dendropsophus microcephalus , Hypsiboas crepitans , H. punctatus , Scinax x-signatus , S. wandae , Elachistocleis aff. ovalis , Leptodactylus sp ., Physalaemus cf. fischeri, Engystomops pustulosus , and Trachycephalus venulosus . In San Vicente , Apure, it is only micro-sympatric with Dendropsophus microcephalus , D. minusculus, Hypsoboas punctatus , and Pseudis paradoxa . In the Maracaibo lake, Zulia, it is micro-sympatric with Dendropsophus microcephalus , Hypsiboas pugnax , Pseudis paradoxa , Leptodactylus sp., Trachycephalus venulosus , Elachistocleis aff. ovalis, and Physalaemus pustulosus ; and syntopic with Pipa parva .

Discussion: Scarthyla vigilans is morphologically and osteologically very similar to S. goinorum . Scarthyla vigilans share with S. goinorum the following characters: (1) nasals large, rounded, with maxillary processes not articulating with maxillae; (2) sphenethmoid ossified, separating nasals and frontoparietals; (3) frontoparietals narrowly separated medially, obscuring frontoparietal fontanelle; (4) squamosal slender; (5) alary processes of premaxillae inclined anteriorly; (6) maxillary arch complete; (7) transverse processes on presacral IV moderately long, inclined posteriorly; (8) sacral diaphyses moderately expanded; (9) intercalary elements between distal and penultimate phalanges ossified. Faivovich et al. (2005) did not presented any synapomorphy for the then monotypic genus. Adding Hyla vigilans to Scarthyla , we either are aware of any synapomorphy within this genus. Even though no synapomorphies are shared by both species, the fact that both are virtually indistinguishable morphologically and osteologically, makes a convincing case to consider Hyla vigilans as a second species of Scarthyla . Although the original description of Scarthyla ostinodactyla (= goinorum ) by Duellman and de Sá (1988) is clear in observing the presence of an “inner tarsal fold […] on distal 2/3 of tarsus”, one of us (JMC) did not observed this character in Colombian specimens assigned to the species (see appendix). These can be due to the fact of the specimens from Colombian Amazonia also could represent S. vigilans , and then, the only striking difference between both species would be the larval characters. Only calls and tadpoles are enough dissimilar between the two species. Call in S. goinorum (as S. ostinodastyla ) was described as series of 8–10 short, whistle-like notes, being the interval between notes of 0.3 sec, and the duration of each note 0.04 sec. The dominant frequency is at 6000 Hz (Duellman and de Sá 1988 ) (see the call of S. vigilans above) The tadpole of S. vigilans was described by Mijares and Hero (1997) and Suárez- Mayorga and Lynch (2001) . Its principal characteristics are: larvae small (TL mean 26.4 mm , maximum TL 31.5), body short, globular, anteriorly subacuminate in lateral view and rhomboidal anteriorly, rounded from above; spiracle sinistral, directed ventrolaterally, attached to body; vent tube medial; tail moderately long, compressed, distally forming a long, rounded tip; dorsal fin shallower than ventral fin, but fin shapes making tail apparently symmetrical; tail musculature weak. Oral disk small, with labial papillae prominent; labial tooth formula 2 (2) / 3 (1); jaw beaks well keratinised, finely serrated. Coloration in life with a remarkable zebra-like pattern of black or dark brown bars separated by translucent bars. The tadpole of S. goinorum is quite unusual, small (TL up to 23.7 mm ), body elongate, twice as long as wide, abruptly terminating posteriorly, eyes large; snout rounded in profile, body shallower than wide; spiracle sinistral, short, directed dorsally; vent tube dextral, short; tail very long, acutely rounded tip, dorsal fin shallower than ventral fin, but both much shallower than in S. vigilans , oral disk with flaplike labia with a single row of pointed serrations; labial tooth formula 2 (1+2)/ 2(1) (following Altig 1970 ). Beak moderately slender, V-shaped, with pointed serrations. Coloration in life, body yellowish green, tail pale green, both with brown markings. Tadpoles of Pseudis paradoxa , P. cardosoi , and Lysapsus limellus are in overall dissimilar from those of S. goinorum and S. vigilans (respectively Emerson 1988 and Duellman 2005 , Kwet 2000 , and Kehr and Basso 1990 ).

Description: We base our description on 21 adults (SVL= 15 mm ) (see Appendix) from the Maracaibo Basin, where the type locality is. Body elongate, slender; head as wide as body, longer than wide; head length 33–42 % of SVL; head width 26–30.8 % of SVL; snout long, acuminate in dorsal and lateral views, projecting well beyond margin of lip; nostrils about 2/3 distance from orbit to tip of snout, slightly protuberant laterally; internarial area slightly concave to flat; canthus rostralis rounded; loreal region barely concave; lips rounded; interorbital area flat, much wider than UEW; IOD 38–46 % of HW; UEW 32–46 % of HW; eye moderately large, protuberant; pupil round, palpebrum clear, tympanum round, TD 42–66% of ED, situated posteroventral to eye, separated from eye by distance equal to half TD; tympanic annulus distinct except on the supero-posterior part, obscured by a diffuse supratympanic fold. Axillary membrane absent; arm moderately slender; ulnar fold and tubercles absent; fingers slender with narrow lateral fringes extending to small round discs ( Fig 3 ); FD equal to 45–70 % TD; relative length of fingers 1<2<4<3; webbing absent; subarticular tubercles small, round, largest on Finger IV; supernumerary tubercles minute, round, in single rows from subarticular tubercles; palmar tubercle low, flat, deeply bifid distally; thenar tubercle low, flat, elliptical; nuptial excrescences absent. Hind limbs slender; tibia length 50–55 % of SVL; foot length 45–50% of SVL; inner tarsal fold absent; outer metatarsal tubercle small, round, flat, half size of inner metatarsal tubercle, indistinct in some specimens; inner metatarsal tubercle small, nearly round; toes slender with small round discs, slightly smaller than those of fingers; relative lengths of toes 1<2<3=5<4; webbing extending to bases of discs on all toes except only to base of penultimate phalange of Toe IV; subarticular tubercles small, round; supernumerary tubercles indistinct, minute, present only on proximal segments ( Fig 4 ). Cloacal opening directed posteriorly at upper level of thighs; cloacal sheath and anal tubercles absent; skin on belly and proximal posteroventral surfaces of thighs granular; skin on other surfaces smooth. Tongue oval to slightly cordiform, not notched posteriorly, free behind for about 1/3 of its length; dentigerous processes of vomers small, each bearing 3–5 teeth; in males, vocal slit extending from midlateral base of tongue to angle of jaw; vocal sac single, median, subgular. Coloration in preservative: dorsum pale brown or pale gray to dark brown or bluish brown, without apparent longitudinal stripes (15%) or with more or less distinct stripes (85%). Three longitudinal stripes, darker than background, usually dark brown, one vertebral, two dorsolateral. Dark brown (sometimes blackish) canthal and supratympanic stripes; supratympanic stripe can extend to above arm or continue to near groin. Hind limbs can be patternless or bearing diffuse markings, like faint spots. Ventral parts creamy white in males, in females white with a few black melanophores (only distinguished by microscope) on throat and chest, immaculate on belly. Iris black or golden, depending on preservation artifacts. Coloration in life: At night, lime green, stripes indistinct, bones pale green; ventral parts transparent. During the day ( Fig. 1 ) the colour is more contrasting. The vertebral line is usually narrower than the dorsolateral ones, and can be surrounded by a narrow whitish line. On the head, the vertebral line can open and form a triangle with the widest part between the interorbital region. Iris bronze, pupil black. Variation: Little variation has been observed. Specimens from Santa María de Caparo (Los Llanos bioregion) have smaller tympanum (30% of ED vs. 50% of individuals from the Maracaibo lake). Osteology: The osteological description is based on MBLUZA–295, a male from Laguna Los Palitos, Sur del lago, Municipio Catatumbo, estado Zulia. The skull is longer than wide, well ossified; the dorsal surfaces ( Fig. 5 ) are smooth and lack exostosis, casquing or co-ossification with the overlying dermis. The nasals are moderately large, triangular, anteriorly separated from the alary processes of the premaxillae by the nasal cartilages. The nasals converge, but do not meet, anteriomedially. Medially, the nasals overlap the lateral margin of the sphenethmoid, and they are almost completely fused with the sphenethmoid. Posteriorly, the nasals are widely separated from the frontoparietals by the ossified sphenethmoid. The frontoparietals are well developed, rectangular, and lack a supraorbital shelf. The medial margins of the frontoparietals are narrowly separated from one another. The frontoparietal fontanelle is covered by the frontoparietals. Posteriorly, the frontoparietals cover the prootics. The sphenethmoid is well ossified; not fused posterolaterally with the prootic like in S. goinorum . The prootics are well ossified and fused with the exoccipitals. The prootic foramen is moderately large and has a complete bony margin. One smaller foramina lies between the optic and prootic foramina. The exoccipitals are well ossified. The crista parotica is short and seems cartilaginous distally. Ventrally ( Fig. 6 ), the parasphenoid is triradiate and smooth. The cultriform process is long and terminates in a sharp tip at the same level of palatines. The parasphenoid alae are narrowly triangular, sharp, and oriented horizontally. The parasphenethmoid is covered anteriorly by the sphenethmoid, and covered posteriorly by the prootic and exoccipitals. The vomers are moderately large and have ovoid, straight odontophores, bearing four teeth each. The neopalatines are sharp and moderately long (barely surpassing the sphenethmoid). The pterygoids are triradiate and slender; the anterior ramus articulates with the maxilla, and the posterior ramus articulates with the squamosal at the level of the angle of the jaw. The medial ramus of the pterygoid has a ligamentous attachment to the anteroventral surface of the otic capsule. The maxillary arches are complete. The premaxillae are separated medially and bear well-developed alary processes that are slightly inclined anteriorly. The partes palatinae and palatine processes are moderately well developed. The maxillae lack pre- and postorbital processes. The quadratojugal is well ossified. Anteriorly, the dentaries are fused, with the Mentomeckelian bones. The presacral vertebrae ( Fig. 7 ) lack neural arches. The transverse processes of all vertebrae are subequal in length, those on presacrals II, III, and VII are oriented transversely, whereas those on presacrals IV –VI are inclined posteriorly, and those on presacral VIII are curved anteriorly. The sacral diapophyses are dilated slightly and in section are more or less cylindrical. The urostyle is moderately short (just a bit less than the total length of column without urostyle) and has a low ridge dorsally basal. Compared with the vertebral columna of S. goinorum (in which the figures of Duellman and De Sá (1988) are reversed), the principal difference is the length of the transverse processes of the vertebrae, being in S. vigilans much longer and the vertebrae much more robust and ossified. The phalangeal formula for the hand and foot is 2-2-3-3 and 2-2-3-4-3, respectively. The intercalary element between the penultimate and distal phalanges is completely ossified. Vocalization and calling behavior: We analysed two series of calls, one from close to the type locality of Scarthyla vigilans ( Fig. 8 ), and other from Los Llanos region, east of the Andes (unfortunately, this last call is too dirty to provide a clear audiospectrogram). The call from the Maracaibo lake area (Finca Onia, 9 km from El Vigía to Colón, estado Mérida) is like a cricket chirp, very low in intensity, each call has between 5 to 6 notes, the first three or four notes have a duration from 0.273 to 0.290 sec, the two other notes are separated by 0.094 sec from the first group of four; the duration of the entire call is 0.35 sec. The separation between calls emitted by the same frog vary from 0.5 sec to 2 sec. The dominant frequency is at 4700 Hz, and the fundamental at 3800 Hz. Another recording from Ologá (not represented), also in the Maracaibo lake, is interesting for showing two more different call types . One is consisting in only two notes, with a total duration of 0.088 sec, with a dominant frequency of 4000 Hz (fundamental at 3400); and another call consisting in four notes, with a total duration of 0.42 sec, a dominant frequency of 4800 Hz and a fundamental frequency of 3800 Hz. The call from near Santa María de Caparo, estado Mérida, in Los Llanos bioregion, is very similar to the one from Finca Onia, with the following variations: the sequence of a single call is a series of six to seven notes, with a duration of about 0.2 sec. There is a group of five notes close together barely separated from the last two. The dominant frequency is lower than the Finca Onia sample, but equal to Ologá sample, at 4000 Hz, and the fundamental frequency is at 3400 Hz. Because the animals of both populations are identical, we consider that the differences between the calls represent intraspecific variation.