On the occurrence of <i>Scinax kennedyi</i> (Pyburn, 1973) (Anura, Hylidae) in the state of Roraima, northern Brazil

Lopes, André Gomes; Giaretta, Ariovaldo Antonio

doi:10.11606/1807-0205/2022.62.036

Abstract

Scinax comprises 129 species of treefrogs divided between the S. ruber and the S. catharinae clades. The S. rostratus group belongs to the S. ruber clade, and comprises ten species characterized by having a dark interorbital triangular mark, tubercle on the heel and by vocalizing in a head-down position. Within this group, S. kennedyi and S. rostratus are similar in that they are the only species that do not possess a row of tubercles on the lower jaw. In spite of their morphological similarity, they can be distinguished from each other by male size and advertisement call traits. Scinax kennedyi was described from eastern Colombia, and occurs from central Colombia to western Venezuela, whereas S. rostratus was described from northern Venezuela, and is thought to occur from Panama to eastern Venezuela, and in the Brazilian state of Pará. A recent study reported a population identified as S. rostratus from the state of Roraima, in northern Brazil. However, this population presented substantial differences in male size and advertisement call in comparison to the described for this species, and apparently it best fits the diagnosis of S. kennedyi instead. In view of this, the present study aimed to clarify the identity of this Brazilian population through a reassessment of its specimens and call recordings, together with the examination of data of S. kennedyi from its type locality, and of S. rostratus from northern Venezuela. Acoustic and morphological analyses revealed that specimens from northern Brazil were indeed misidentified as S. rostratus, and hence they were herein reassigned to S. kennedyi. The study therefore demonstrates the occurrence of S. kennedyi in Brazil, extending its distribution ca. 1,120 km east by south from its type locality, and ca. 844 km east-southeast from its easternmost previous record. With this reassessment, a clearer acoustic diagnosis between S. kennedyi and S. rostratus was provided, as well as further data on fine-scale temporal traits of their calls.

Keywords. Advertisement call; Amazon Basin; Bioacoustics; Geographic distribution; Scinax rostratus group

INTRODUCTION

As presently defined, Scinax Wagler, 1830 comprises 129 species of treefrogs (Frost, 2022) allocated into the S. catharinae and S. ruber clades (sensuFaivovich et al., 2005). The S. ruber clade contains 77 species, of which ten are assigned to the S. rostratus group and three to the S. uruguayus group (Faivovich et al., 2005; Baldo et al., 2019), while the remaining are not assigned to any group until the present moment. The S. rostratus group was first proposed by Duellman (1972) and supported as monophyletic by subsequent morphological and molecular studies (e.g.,Faivovich, 2002; Faivovich et al., 2005). Its species are characterized mainly by having a dark triangular mark between the eyes and tubercle on the heel [this latter character may be absent in S. kennedyi (Pyburn, 1973) and S. rostratus (Peters, 1863) (Faivovich et al., 2005; present study)], in addition to typically calling in a vertical head-down position (Duellman, 1972; Faivovich, 2002; Faivovich et al., 2005).

Among the species of the Scinax rostratus group, S. kennedyi and S. rostratus are the only ones that do not possess a row of tubercles on the edge of the lower jaw (Duellman, 1972; Pyburn, 1973; Duellman & Wiens, 1992; Lescure & Marty, 2000; Lima et al., 2004). Although they are similar regarding this aspect, they differ from each other mainly in male size, with S. kennedyi having smaller snout-vent length (SVL) (31.1-35.3 mm vs. 40-45.7 mm in S. rostratus;Duellman, 1970; Pyburn, 1973), and in advertisement call traits (León, 1969; Duellman, 1972; Pyburn, 1973). Scinax kennedyi was described from “ca. 110 mi ESE Puerto Gaitán, Departamento de Meta, Colombia”, and occurs in central and eastern Colombia, and in westernmost Venezuela (Pyburn, 1973; Angarita-Sierra et al., 2013; Pedroza-Banda et al., 2014; Acosta-Galvis 2018a, b). Scinax rostratus was described from Caracas, northern Venezuela, with occurrences reported from Panama to eastern Venezuela, and also from two localities in the Brazilian state of Pará, geographically disjunct from the remaining of its distribution records (Peters, 1863; Rivero, 1968; Duellman, 1972; Gorzula & Señaris, 1998; Nieto-Castro, 1999; Barrio-Amorós et al., 2004, 2019; Sturaro et al., 2010).

Recently, Bang & Giaretta (2017) reported a population identified as Scinax rostratus from the state of Roraima, northern Brazil, thus supposedly filling this gap in the species’ distribution. However, these specimens have smaller size than the reported in literature for this species (León, 1969; Duellman, 1970, 1972; Sturaro et al., 2010), and calls with substantially lower pulse rate and lower dominant frequency of both emphasized frequency bands in comparison to the previously reported (León, 1969; Duellman, 1972). Actually, the traits Bang & Giaretta (2017) described for this population best fit the diagnosis of S. kennedyi. In view of these discrepancies, the present study aims to clarify the identity of this Brazilian population based on the re-examination of the data presented in Bang & Giaretta (2017), together with the examination of data of S. rostratus from northern Venezuela, and of topotypic S. kennedyi.

MATERIAL AND METHODS

Data acquisition

Specimens and call recordings presented in Bang & Giaretta (2017), deposited in the Collection of Frogs of the Museu de Biodiversidade do Cerrado (Universidade Federal de Uberlândia; AAG-UFU), were reanalysed. These data were obtained on 27-28 July 2016, in the municipality of Cantá, state of Roraima, Brazil [02°45′59.0″N, 60°36′32.0″W; 70 m above sea level (asl); datum WGS84] (Fig. 1). Recordings were made with a Sennheiser® K6/ME67 directional microphone connected to a Marantz® PMD 671 digital recorder (sampling rate of 44.1 kHz; 24-bits resolution).

Figure 1
Distribution records of Scinax kennedyi [yellow star = type locality (approximation); black dots = literature records (Pyburn, 1973; Angarita-Sierra et al., 2013; Pedroza-Banda et al., 2014; Acosta-Galvis, 2018a, b); red square = new record] and S. rostratus [white cross = type locality; white dots = literature records (Rivero, 1968; Duellman, 1972; Gorzula & Señaris, 1998; Nieto-Castro, 1999; Barrio-Amorós et al., 2004; Sturaro et al., 2010); white diamond = Guaráunos, state of Sucre (data herein examined)]. Abbreviations of the Brazilian states: AM (Amazonas), AP (Amapá), PA (Pará), and RR (Roraima). Specimen in the upper left area: Scinax kennedyi (AAG-UFU 5573; SVL = 31.8 mm) from municipality of Cantá, state of Roraima, Brazil.

Recordings of Scinax kennedyi presented in Pyburn (1973), deposited in the Macaulay Library collection (Cornell Lab of Ornithology), were also reanalysed. These were obtained on 13 April 1971, in the species’ type locality (ca. 110 mi ESE Puerto Gaitán, Departamento de Meta, Colombia; ca. 03°46′35.2″N, 70°37′48.4″W; 179 m asl) (Fig. 1). Recordings were made with a Uher® 4000 Report-L recorder (digitized at a sampling rate of 44.1 kHz and 16-bits resolution). Although none of the recorded specimens were collected, they were recorded at the same site and date the holotype was collected (Pyburn, 1973).

Specimens and recordings of Scinax rostratus, respectively deposited in the KU Herpetology collections (University of Kansas; KUH) and in the Macaulay Library collection (Cornell Lab of Ornithology), were analysed. These data were obtained on 28 July 1974, nearby Guaráunos, Río Sabacual, state of Sucre, northern Venezuela (ca. 10°30′16.3″N, 63°07′54.5″W; 23 m asl), located ca. 413 km east from the species’ type locality (Fig. 1). Recordings were made with a Uher® microphone connected to a Uher® 4000S recorder (digitized at a sampling rate of 96.0 kHz; 24-bits resolution). See Appendices 1 and 2 for further details on specimens and recordings herein examined, respectively.

Acoustic analyses

Calls were analysed in Raven Pro v.1.5 software (K. Lisa Yang Center for Conservation Bioacoustics, 2014) with the following settings: window size = 256 samples; 3 dB filter bandwidth = 248 or 539 Hz; window type = Hann; overlap (locked) = 89.8%; hop size = 0.271 or 0.590 ms; DFT size = 1,024 samples; grid spacing = 43.1 or 93.8 Hz. High-pass filters up to 500 Hz and low-pass filters up to 5,000 Hz were applied to the recordings to reduce background noise. Dominant, maximum, and minimum frequencies were respectively obtained with the “Peak Frequency”, “Frequency 95%”, and “Frequency 5%” functions of the software. Pulse rate was measured from a 100 ms section in the middle of the call, as follows: (number of pulses - 1)/time between the onset of first and last pulse. It was adopted the call-centered approach sensuKöhler et al. (2017). Acoustic terminology and definitions followed Köhler et al. (2017). Sound figures were produced in R platform v.3.6.2 (R Core Team, 2019) with seewave v.2.1.6 (Sueur et al., 2008) and tuneR v.1.3.3 (Ligges et al., 2018) packages, under the following settings: window = Hanning; overlap = 85%; FFT = 256.

RESULTS

Specimen identification

Specimens from Cantá (Roraima, Brazil) (n = four males; two being call vouchers) match the diagnosis provided in the original description of Scinax kennedyi by Pyburn (1973), being diagnosed by the following combination of traits: (1) snout-vent length (SVL) of 31.8-34.3 mm in males; (2) absence of a row of tubercles in the lower jaw; (3) extremely reduced, rounded heel tubercle (absent in AAG-UFU 5575); (4) dark interorbital triangular mark (apex directed posteriorly) edged with a pale cream line; (5) dark dorsum, with some individuals having a nearly smooth skin texture bearing very few, small, rounded tubercles (AAG-UFU 5575-76), whereas other individuals have a more (albeit still moderately) tuberculate skin texture (AAG-UFU 5573-74); (6) broad orange and black (in life; colours respectively become creamy white and black in preservative) vertical bars on anterior and posterior surfaces of thigh, and inner surface of tarsus; (7) dark transverse bars on upper surfaces of tibia and forearm; (8) snout slightly acuminate, projecting beyond the margin of lower jaw, and lacking a fleshy proboscis.

Specimens from Guaráunos (Sucre, Venezuela) (n = two; both being call vouchers) match the diagnoses of Scinax rostratus provided by Duellman (1970, 1972), being diagnosed by the following combination of traits: (1) SVL of 41.59-43.27 mm in males; (2) absence of a row of tubercles in the lower jaw; (3) extremely reduced, rounded heel tubercle; (4) dark interorbital triangular mark (apex directed posteriorly); (5) pale brown (in preservative) dorsum, with nearly smooth skin texture; (6) broad creamy white and dark brown (in preservative) vertical bars on anterior and posterior surfaces of thigh, and inner surface of tarsus; (7) dark transverse bars on upper surfaces of tibia and forearm; (8) snout broad, acutely rounded, projecting beyond the margin of lower jaw, and lacking a fleshy proboscis.

As depicted above, Scinax kennedyi and S. rostratus turned out to be quite similar to each other, so that morphological and chromatic traits traditionally used in their respective diagnoses, although useful to distinguish them from the remaining species of the S. rostratus group, were not enough to unambiguously separate one from the other. The only character that proved to be reliable to establish a clear differential diagnosis between the two species was the male SVL, since examined males of S. kennedyi have smaller SVL than those of S. rostratus (no overlap of values).

Description of advertisement calls

The advertisement calls from Cantá (Fig. 2A) and of the topotypes of Scinax kennedyi (Fig. 2B) have the same structural pattern and very similar trait values. These calls consist of a single multi-pulsed note with variable durations and intervals. The first pulse has a remarkably smaller amplitude, whereas all other pulses share with each other nearly the same amplitude level. Pulses are well-spaced from each other (Figs. 3A, B), usually have slight internal amplitude modulations, and in general the first pulse is longer than the others. Calls have two emphasized frequency bands, hereinafter referred to as the lower (LFB) and the higher (HFB) frequency bands, with the dominant frequency being able to alternate between both along call emissions [as it is common in calls of several Scinax species; e.g.,Magrini et al. (2011); Novaes & Zina (2016)]. Regarding the Brazilian population, the dominant frequency corresponded only to the HFB in five individuals, only to the LFB in one individual, and alternated between both bands along call emissions of one individual; regarding the topotypic population, the dominant frequency corresponded only to the LFB in all individuals.

Figure 2
Audiospectrograms (above) and respective oscillograms (below) of the advertisement calls of: (A) Scinax kennedyi from municipality of Cantá, state of Roraima, Brazil (sound file: Scinax_kennedyiCantaRR3aAAGm671); (B) S. kennedyi from its type locality (ca. 110 mi ESE Puerto Gaitán, Departamento de Meta, Colombia) (sound file: ML218364); (C) S. rostratus from Guaráunos, state of Sucre, Venezuela (sound file: ML194689).

Figure 3
Audiospectrograms (above) and respective oscillograms (below) of sections of ca. 0.22 s extracted from the middle portion of each call depicted in , detailing the pulse emission pattern: (A) Scinax kennedyi from municipality of Cantá, state of Roraima, Brazil; (B) S. kennedyi from its type locality (ca. 110 mi ESE Puerto Gaitán, Departamento de Meta, Colombia); (C) S. rostratus from Guaráunos, state of Sucre, Venezuela. Notice the substantially shorter pulse intervals (= higher pulse rate) of the call of S. rostratus.

The advertisement call of Scinax rostratus from northern Venezuela (Fig. 2C) consists of a single multi-pulsed note with variable durations and intervals. It has an ascending amplitude modulation at its onset, and quickly reaches a level that is sustained over its duration with minimal variations. Pulses are spaced from each other by very short intervals (Fig. 3C) and have internal amplitude modulations. Calls have two emphasized frequency bands, the LFB and the HFB, with the dominant frequency being able to alternate between both along call emissions. The dominant frequency corresponded only to the HFB in one individual, whereas it alternated between both bands along call emissions of the other individual. Descriptive statistics of the call of each species are provided in Table 1.

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Table 1
Advertisement call trait values of the populations of Scinax kennedyi and S. rostratus studied here. N = recorded individuals/calls analysed. Values are given as mean ± SD (minimum-maximum).

DISCUSSION

The call trait values resulting from the present reanalysis are congruent with those reported by Bang & Giaretta (2017) and those of topotypic Scinax kennedyi reported by Pyburn (1973). However, Pyburn (1973) reported a third emphasized frequency band at about 1,700 Hz in some calls, which was not detected here. The analysis of the call recordings of S. rostratus from Guaráunos (northern Venezuela) retrieved trait values similar to those previously reported for this species (seeLeón, 1969; Duellman, 1970, 1972). However, León (1969) and Duellman (1970) reported a fundamental frequency around 56 Hz, which is an unrealistic value for the call of this species. Such minor differences between our results and literature data are most likely due to the limited technology for call analysis available at that time.

The reassessment of the call recordings presented in Bang & Giaretta (2017) demonstrated that the call of the Brazilian population does not match neither in structure nor in trait values with the call of Scinax rostratus, thus contradicting their species identification. Contrariwise, the call of this population matched in structure and trait values to the topotypic call of S. kennedyi. A minor difference was observed in pulse intervals, with calls from Brazil having slightly shorter pulse intervals (which reflected in its slightly higher pulse rate) in comparison to the topotypic calls. Nevertheless, such small variation in temporal trait values may be explained by the considerable difference in temperature (ca. 3℃) between both localities (^{Appendix 2} APPENDIX 2 List of analysed sound files (.wav) for each species, with the associated metadata. * Species’ type locality. Label/catalogue number Voucher Time (h) Date Air (ºC) Scinax kennedyi (Cantá, Roraima, Brazil) Scinax_kennedyiCantaRR3aAAGm671 AAG-UFU 5573 19:31 27 Jul 2016 28 Scinax_kennedyiCantaRR4aAAGm671 - 19:34 27 Jul 2016 28 Scinax_kennedyiCantaRR4bAAGm671 - 19:35 27 Jul 2016 28 Scinax_kennedyiCantaRR5aAAGm671 AAG-UFU 5574 19:56 27 Jul 2016 28 Scinax_kennedyiCantaRR7aAAGm671 - 19:44 28 Jul 2016 29 Scinax_kennedyiCantaRR8aAAGm671 - 19:49 28 Jul 2016 29 Scinax_kennedyiCantaRR9aAAGm671 - 19:50 28 Jul 2016 29 Scinax_kennedyiCantaRR10aAAGm671 - 20:09 28 Jul 2016 29 Scinax kennedyi (ca. 110 mi ESE Puerto Gaitán, Departamento de Meta, Colombia)* ML218364 - - 13 Apr 1971 25 ML218367 - - 13 Apr 1971 25 ML218368 - - 13 Apr 1971 - Scinax rostratus (Guaráunos, Sucre, Venezuela) ML194688 KUH 167017 19:25 28 Jul 1974 24 ML194689 KUH 167018 19:30 28 Jul 1974 24 ; Table 1), since it is known that temperature may exert considerable influence on such fine-scale temporal traits of advertisement calls of frogs (Gerhardt, 1994; Valetti & Martino, 2012; Köhler et al., 2017). In addition to this, males from Brazil matched the morphological diagnosis provided for S. kennedyi in Pyburn (1973), thus corroborating the acoustic identification.

Therefore, it is demonstrated here that Scinax kennedyi and S. rostratus can be clearly acoustically distinguished from each other. The advertisement call of S. kennedyi has longer pulse intervals, substantially lower pulse rate, first pulse with considerably longer duration, higher minimum frequency, and higher dominant frequencies of both LFB and HFB (Table 1). Moreover, there is also difference in the structure of the calls of these species (seeFig. 2; see Results section). In addition to the acoustic diagnosis, it is important to note that although these species are morphologically similar to each other, there is an expressive difference in the SVL of males that allows for a straightforward differentiation between them, with males of S. kennedyi being smaller than those of S. rostratus.

Concluding, the population from Cantá was misidentified as Scinax rostratus by Bang & Giaretta (2017), and hence it is herein reassigned to S. kennedyi. Therefore, this is the first study to recognize the occurrence of S. kennedyi in Brazil, thus extending its distribution ca. 1,120 km east by south from its type locality, and ca. 844 km east-southeast from its previously known easternmost locality (Puerto Ayacucho, state of Amazonas, Venezuela; Fig. 1). This is now the southernmost and easternmost occurrence of this species. It is possible that new populations of S. kennedyi in eastern/southeastern Venezuela will be revealed by future research. That said, the previously existing gap in the southeastern portion of the distribution of S. rostratus still remains (Fig. 1). Besides extending the distribution of S. kennedyi, the present study provided a clearer acoustic diagnosis between S. kennedyi and S. rostratus, and presented new data on fine-scale temporal traits of their calls. Such contribution is relevant as it may help future studies to more accurately identify new populations of the species studied here.

ACKNOWLEDGMENTS

The associate editor Dr. Pedro M.S. Nunes and two anonymous reviewers made valuable suggestions that helped to improve the quality of this work. The Cornell Lab of Ornithology (Bioacoustics Research Program) provided a free license of Raven Pro software to AGL. The staff of the KU Herpetology collections of the University of Kansas (namely: Dr. Rafe Brown, Camila Meneses, and Melissa Mayhew) kindly provided measurements, specific observational notes, and detailed, high-resolution photographs of the S. rostratus specimens from Venezuela. The Macaulay Library at the Cornell Lab of Ornithology allowed access to the recordings of topotypic Scinax kennedyi and of S. rostratus from Venezuela. Dr. William F. Pyburn made the recordings of topotypic S. kennedyi. Dr. William E. Duellman collected and recorded the S. rostratus specimens from Venezuela. This paper is dedicated to the memory of Dr. William E. Duellman in recognition of his outstanding scientific contributions over many decades.

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FUNDING INFORMATION: The CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) provides a research grant to AAG (#300903/2015-4; #305169/2019-0), and provided a M.Sc fellowship to AGL (#130380/2020-2).
Published with the financial support of the "Programa de Apoio às Publicações Científicas Periódicas da USP".

APPENDIX 1

List of examined specimens (call vouchers indicated in bold).

Scinax kennedyi: BRAZIL, state of Roraima, municipality of Cantá: AAG-UFU 5573-74, 5575-76.

Scinax rostratus: VENEZUELA, state of Sucre, Guaráunos, Río Sabacual: KUH 167017-18 (high-resolution photographs).

APPENDIX 2