Bioacoustics of Scinax x-signatus

The advertisement call of Scinax x‑signatus consists of a single multipulsed note,emitted at a highly variable repetition rate (2-105 notes/minute; Table 2 ; Fig. 10A ), which is likely affected by conspecific chorus density, since the longer intervals between notes (up to 25.3 s ; Table 2 ) were observed in the recording of the neotype , which was calling alone with no nearby conspecific. Notwithstanding, much longer intervals are the exception, and the notes are repeated at faster rates (29-105 notes/minute; Table 2 ), but never composing a stereotyped series. Note duration is 0.11- 0.25 s ( Table 2 ; Fig. 10 A-C); each note is composed of 6-14 pulses with modulating amplitude increasing from the first third, reaching the maximum amplitude around the middle of the note,and gradually decaying towards the last pulse ( Fig. 10B, C ). Pulse rate is 52-64 pulses/s and pulse duration 0.013 - 0.018 s ( Fig. 10B, C ). Calls have a broadband spectrum (BW90% 2250-2799 Hz; Table 2 ; Fig. 10C ). The power spectrum is usually biphasic, with two main emphasized frequency bands ( Fig. 10C ). The lower band ( i.e., the low-frequency band) comprises most of the power of the spectrum, with the dominant frequency ranging between 904-1359 Hz ( Fig. 10C ), and also including part of the freq5% (861-991 Hz; Table 2 ). The upper band ( i.e., the high-frequency band) has less power than the first one, surrounding the freq95% (3188-3704 Hz; Table 2 ), with its peak frequency between 2885-3618 Hz ( Fig. 10C ). Between the two power spectrum bands, there is a low-power“valley” (or gap) around 2.0-2.5 kHz ( Fig. 10C ). The dominant frequency does not alternate between the lower and upper bands, remaining in the lower band.

Scinax x‑signatus is a species of Scinax , as it shares three synapomorphies of this genus: webbing between toes I and II that does not extend beyond the subarticular tubercle of toe I; origin of the m. pectoralis abdominalis through well-defined tendons; and m. pectoralis abdominalis overlapping m. obliquus externus ( da Silva, 1998 ; Faivovich, 2002 ; Faivovich et al., 2005). A single synapomorphy is known for the S.ruber Clade: tadpoles with the vent tube above the margin of the lower fin ( Faivovich, 2002 ; Faivovich et al., 2005). While tadpoles unequivocally associated to S. x‑signatus remain unknown, this species was associated to the S. ruber Clade by having the unique combination of external vocal sac and presence of pectoral fold [internal vocal sac and pectoral fold absent in most species of the S. catharinae Clade; in few species where the vocal sac is external, the pectoral fold is absent ( e.g., S. garibaldiae , S. rizibilis ); otherwise, in the two cases where the pectoral fold is present, the vocal sac is internal ( S.agilis and S.melanodactylus ); J.Faivovich & K. Araujo-Vieira, pers. obs.; see also Bokermann, 1964 ; Cruz & Peixoto, 1982 ; Faivovich, 2002 ; Lourenço et al., 2014, 2019]. Scinax x‑signatus can be differentiated from all other species of the S. ruber Clade by the combination of the following characters: (1) male SVL 34.5-38.4 mm, n = 13; (2) snout rounded in dorsal view and profile; (3) pointed tubercles on lower jaw absent; (4) vocal sac subgular, weakly bilobate; (5) spicule-shaped papillary epidermal projections on the nuptial pads and pectoral region present in males; (6) pectoral glands present in males; (7) dorsal color pattern with large irregular dark blotches, commonly with dark X-shaped mark composed of one or two pairs of inverted parenthesis-like blotches; (8) hidden surfaces of thighs dark with irregular pale blotches, yellow in living specimens; (9) iris yellowish golden or bronze with a median black streak; (10) physiological chlorosis absent; and (11) advertisement call composed of a single, multipulsed note, 0.11- 0.25 s duration, 6-14 pulses/note, 52-64 pulses/s.

The SVL in males of Scinax x‑signatus (34.5-38.4 mm, n = 13) distinguishes it from the larger species S. castroviejoi and S.eurydice (SVL males 44.0-52.0 mm; De la Riva, 1993 ; Bokermann, 1968 ), and from the smaller species S. altae , S. auratus , S. cabralensis , S. caldarum , S. cruentomma , S. danae , S. exiguus , S. fuscomarginatus , S. juncae , S. karenanneae , S. lindsayi , S. madeirae , S. maracaya , S. ruberoculatus , S. rupestris , S. staufferi , S. strussmannae , S. tymbamirim , S. villasboasi , and S. wandae (SVL males 15.7-29.0 mm; Lutz, 1968 , 1973 ; Duellman, 1970 , 1986 ; Pyburn & Fouquette, 1971 ; Cardoso & Sazima, 1980 ; Duellman & Wiens, 1993 ; Pyburn, 1992 , 1993 ; Drummond et al., 2007; Nunes & Pombal, 2010 , 2011 ; Nunes et al., 2012; Brusquetti et al., 2014; Araujo-Vieira et al., 2015; Ferrão et al., 2018a, b). The snout rounded in dorsal view and profile differentiates Scinax x‑signatus from S. alter , S. auratus , S. cretatus , S. crospedospilus , S. imbegue , S. juncae , and S. tymbamirim (sub-elliptical with a pointed tip in dorsal view and slightly acute in profile), S.fuscovarius (roundly acute in dorsal view and protruding in profile), S. caldarum , S. curicica , S. duartei , S. maracaya , S. rossaferesae , and S. tigrinus (sub-elliptical or subovoid in dorsal view and slightly acute in profile), S. squalirostris (pointed in dorsal view and acute in profile), and species of the S. rostratus group (elongate pointed in dorsal view and acute with or without a fleshy proboscis in profile). Furthermore, the absence of pointed tubercles on the lower jaw differentiates S. x‑signatus from almost all species of the S. rostratus Group; exceptions are S.kennedyi and S.rostratus ( e.g., Duellman, 1972 a , 1973; Pyburn, 1973 ; Lescure & Marty, 2000 ; Lima et al., 2005; this study). The presence of a weakly bilobate subgular vocal sac in Scinax x‑signatus distinguishes it from S.camposseabrai (bilobate subgular vocal sac; see also Caramaschi & Cardoso, 2006 : fig. 1) and from the remaining species of the S. ruber Clade with single subgular vocal sac;exceptions are S.acuminatus , S.dolloi , S.funereus , S.fuscovarius , S.hayii , S.karenanneae , S.montivagus , S.onca , S.oreites , S.pachycrus , S.perereca , S. ruberoculatus , and S.tsachila , that have a weakly bilobate subgular vocal sac ( e.g., Cei, 1980 ; Duellman & Wiens, 1993 ; Pyburn, 1993 ;Ferrão et al., 2017, 2018a; this study). The presence of spicule-shaped papillary epidermal projections on the nuptial pad and pectoral region in males differentiates Scinax x‑signatus from all other species of the S. ruber Clade, except for S. fuscovarius (see also Luna et al., 2018: fig. 10A, C). The presence of pectoral glands in males differentiates S. x‑signatus from most species of the S. ruber Clade, except for S. funereus , S.fuscovarius , S.nasicus , S.onca , and S.similis , and species of the S. uruguayus Group ( e.g., Müller & Hellmich, 1936 ; Lutz, 1973 ; Cei, 1980 ; this study). The dorsal pattern with large irregular dark blotches, commonly with dark X-shaped marks composed of one or two pairs of inverted parenthesis-like blotches, distinguishes Scinax x‑signatus from S. altae , S. alter , S. auratus , S. boesemani , S. caldarum , S. cretatus , S. crospedospilus , S. curicica , S. cuspidatus , S. duartei , S. exiguus , S. fuscomarginatus , S. imbegue , S. juncae , S. madeirae , S. oreites , S. pachycrus , S. quinquefasciatus , S. ruber , S. squalirostris , S. staufferi , S. tsachila , S. tymbamirim , and S. villasboasi (variable number of dorsal and/or lateral stripes; e.g., Duellman, 1970 ; Lutz, 1973 ; Duellman & Wiens, 1993 ; Pugliese et al., 2004; Nunes et al., 2012; Brusquetti et al., 2014; Ron et al., 2018; this study), and S. blairi , S. cabralensis , S. chiquitanus , S. danae , S. iquitorum , S. lindsayi , S. maracaya , and S. strussmannae (scattered or homogeneously distributed spots and/or irregular blotches; e.g., Fouquette & Pyburn, 1972 ; Cardoso & Sazima, 1980 ; De la Riva, 1990 ; Drummond et al., 2007; Ferrão et al., 2018b; this study). The hidden surfaces of thighs dark colored with light irregular pale blotches, yellow in living specimens differentiate Scinax x‑signatus from S. altae , S. auratus , S. baumgardneri , S. boesemani , S. cretatus , S. crospedospilus , S. cruentomma , S. cuspidatus , S. danae , S. elaeochroa , S. exiguus , S. fuscomarginatus , S. ictericus , S. iquitorum , S. madeirae , S. manriquei , S. pachycrus , S. ruberoculatus , S. staufferi , S. strussmannae , S. squalirostris , S. tsachila , S. villasboasi , S. wandae , and species of the S. uruguayus Group (hidden surfaces of thighs uniform, light or dark colored; e.g., Rivero, 1961 ; Duellman, 1970 , 1986 ; Lutz, 1973 ; De la Riva, 1990 ; Duellman & Wiens, 1993 ; Barrio-Amorós et al., 2004; Nunes & Pombal, 2011 ; Brusquetti et al., 2014; Ferrão et al., 2018a, b; Ron et al., 2018; Baldo et al., 2019; this study), S. funereus , S. onca , and S. iquitorum (hidden surfaces of thighs with horizontal or irregular dark blotches; Duellman, 1971 ; Ferrão et al., 2017; Moravec et al., 2009; this study), and from species of the S. rostratus Group (hidden surfaces of thighs uniform light or marked with bold dark and light mottling or broad vertical bars; Duellman, 1972 a , 1973; Henle, 1991 ; Lescure & Marty, 2000 ; Lima et al., 2005; this study). The yellowish golden or bronze iris, with a median black streak, distinguishes Scinax x‑signatus from S. cruentomma (silvery bronze iris, with a median red streak; Duellman et al., 1972b ), S. ruberoculatus (bicolored, reddish upper half and grey lower half; Ferrão et al., 2018a), and species of the S. uruguayus Group (bicolored, golden upper half and dark brown to black lower half; Baldo et al., 2019). The absence of physiological chlorosis in S. x‑signatus distinguishes it from S. boesemani , S. caprarius , S. cruentomma , S. cuspidatus , S. elaeochroa , S. funereus , S. ictericus , S. iquitorum , S. karenanneae , S. manriquei , S. onca , S. strussmannae , and S. tsachila (present in these species; León, 1969 ; Lutz, 1973 ; Pyburn, 1993 ; La Marca, 2004 ;Moravec et al., 2009;Cole et al., 2013; Melo-Sampaio & Souza, 2015 ; Ferrão et al., 2017, 2018b; Acosta-Galvis, 2018 ; Ron et al., 2018;Taboada et al., 2020). The advertisement call composed of a single multipulsed short note (0.11- 0.25 s ), with 6-14 pulses/note, and pulse rate of 52-64 pulses/s differentiates Scinax x‑signatus from S. castroviejoi and S. eurydice (two or three multipulsed notes; De la Riva, 1993 ; De la Riva et al., 1994; Pombal et al., 1995a; Magrini et al., 2011; Mângia et al., 2017), S. alter , S. curicica , and S. perereca (note duration 0.28- 4.5 s and 21-152 pulses/note; Pombal et al., 1995a, b; Pugliese et al., 2004), S. cruentomma , S. fuscomarginatus , and S. strussmannae (17-90 pulses/note and 113-272 pulses/s; De la Riva et al., 1994; Duellman, 1972b ; Brusquetti et al., 2014; Carvalho et al., 2015;Ferrão et al., 2018b), S. exiguus (23-90 pulses/note; Carvalho et al., 2017), S. madeirae (note duration 0.72- 1.16 s and 104-145 pulses/s; Brusquetti et al., 2014), S. staufferi (100-130 pulses/s; León, 1969 ), S. wandae (note duration 0.44- 0.69 s and 70-108 pulses/note; Pyburn & Fouquette, 1971 ; Duellman, 1986 ; Pombal et al., 2011), and from some large species of the S. rostratus Group: S. boulengeri and S. proboscideus (80-230 pulses/s; León, 1969 ; Duellman, 1972a ), S. jolyi (note duration 2.5 s and 180 pulses/note; Lescure & Marty,2000 ), S.kennedyi (note duration 0.66- 2.9 s ; Pyburn, 1973 ),and S.sugillatus (note duration 0.28- 0.60 s and 110-140 pulses/s; Duellman, 1973 ).