Herpetology Notes, volume 10: 387-389 (2017) (published online on 06 July 2017)
Distress calls of Leptodactylus macrosternum Miranda-Ribeiro, 1926 (Anura: Leptodactylidae) during a cannibal attack Lucas Rodriguez Forti1,3, Jackson Cleiton Sousa2 and Carlos Eduardo Costa-Campos2
Abstract. Distress calls emitted by prey should reduce the success of predators during the agonistic interaction. Many species of anurans are capable of producing distress calls as a defensive behaviour. However, formal bioacoustic analyses of such signals are still incipient. We describe for the first time the distress call of a juvenile Leptodactylus macrosternum, which was emitted during a cannibal attack by an adult. We analysed 12 distress calls, which were composed by a harmonic structure with multiple pulses and large range frequency. Other leptodactylids have very similar distress calls. However, high variation in some call properties, such as call duration, should be a common feature of distress calls in this genus. Our work contributes novel information on the bioacoustics of Neotropical anurans. Keywords: Amphibia, bioacoustics, defensive behaviour, predation
Frogs are victims of many kinds of predators in all stages of their lives (Wells, 2007). Post-metamorphic individuals are especially vulnerable and appreciated by many arthropods (Toledo, 2003; Castanho and Rocha, 2005; Menin et al., 2005; Forti et al., 2007), snakes, birds, mammals, and surprisingly by other amphibians (Toledo et al., 2007; Measey et al., 2015). Therefore, it is undeniable that the success of anurans, as a highly diverse group (Pough et al., 2016), is clearly linked to the evolution of several elaborated defence mechanisms for reducing predation (Toledo and Haddad, 2009a; Toledo et al., 2011). The distress call is one of the more relevant defence mechanisms in the anuran behavioural repertoire (Toledo et al., 2007; Toledo and Haddad, 2009a; b; Toledo et al., 2011). Generally, distress calls are loud with a large frequency range and the presence of harmonic
Laboratório Multiusuário de Bioacústica (LMBio) e Laboratório de História Natural de Anfíbios Brasileiros (LaHNAB), Departamento de Biologia Animal, Instituto de Biologia, Universidade Estadual de Campinas, Caixa Postal 6109, 13083-970, Campinas, São Paulo, Brazil. 2 Laboratório de Herpetologia, Departamento de Ciências Biológicas e da Saúde, Universidade Federal do Amapá, Campus Marco Zero do Equador, 68.903-419, Macapá, AP, Brasil. 3 Corresponding author: e-mail:
[email protected] 1
structures (Toledo and Haddad, 2009b). These acoustic signals may startle acoustically oriented predators, and prey animals may gain some seconds to escape (Bogert, 1960; Toledo and Haddad, 2009b). Herein we describe for the first time the distress call of a juvenile Leptodactylus macrosternum, which was emitted during a cannibal attack by an adult. We opportunistically obtained this record during fieldwork for a rapid amphibian and reptile assessment at a flooded area, municipality of Santana, State of Amapá, Brazil. Details on this event can be found in Sousa et al. (2016). Leptodactylus macrosternum has a large geographical distribution, occurring in Colombia, Venezuela, Brazil, the Guianas, Bolivia and Trinidad, with a topotypical population from Salvador, state of Bahia, Northeastern Brazil (Frost, 2017). This species may be attacked by several kinds of predators, such as snakes, birds, other frogs and insects (Pereira et al., 2011; Andrade et al., 2013; Oliveira et al., 2014; Sousa et al., 2016). Equivalently, L. macrosternum may be considered a generalist predator and may consume different prey items (Silva-da-Costa et al., 2016). Our naturalistic observation was documented partially with a Cannon PowerShot SX60 HS digital camera. We used the software Adobe Audition 8.1.0 to convert the video extension (mp4) to a readable sound file (wav) with 44.1 kHz and 24 bits of resolution and for confection
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Figure 1. Power spectrum (above left); coefficient of variation of call properties: BF – Band Frequency; MIF – Minimum Frequency; DF – Dominant Frequency; MAF – Maximum Frequency; CD – Call Duration; PN – Pulse Number; TMA – Rise Time to the Maximum Amplitude (above right), oscillogram (middle) and spectrogram (below) of the distress call of a Leptodactylus macrosternum juvenile (SVL = 38.6 mm), recorded in the municipality of Santana, State of Amapá, Northern Brazil.; Temperature = 26.5 0C.
of figures. The audio and the video recording were deposited at Fonoteca Neotropical Jacques Vielliard with the following access codes: FNJV 33722 and 1000391. We analyzed 12 distress calls emitted by a juvenile L. macrosternum while it was attacked by an adult individual. Before the bioacoustical analysis, calls were normalized individually at -1 dB using the software Audacity 2.1.2. All vocalizations were analysed with Raven Pro 1.4 (Bioacoustic Research Program, 2011), measuring the follow acoustic traits: (1) call duration (s); (2) number of pulses; (3) rise time to the maximum amplitude (s); (4) minimum frequency (Hz); (5) peak of dominant frequency (Hz); (6) maximum frequency (Hz); and (7) frequency bandwidth (as maximum subtracted by minimum) (Hz). Spectral measurements were
Lucas Rodriguez Forti et al. obtained using a FFT (Fast Fourier Transform) of 1024 and 50 % of overlapping. We selected the calls using the waveform. We used the following Raven functions to measure the acoustic properties: (1) delta time; (2) frequency 5% (for the minimum frequency, ignoring 5% below the total energy in the selected call); (3) frequency 95% (for the maximum frequency, ignoring 5% above the total energy in the selected call); (4) Max frequency (for the peak of dominant frequency); (5) bandwidth 90% (for the frequency bandwidth, a band of frequency that includes 90% of the energy of the sound), and (6) Max amplitude (u). We calculated the variation on call properties using the coefficient of variation, obtained by the follow equation: CV = Standard Deviation / Mean x 100 (value in percentage). Distress calls are composed by a harmonic structure with multiple pulses and a large range frequency (Figure 1). Call duration is 0.372 ± 0.050 s (0.284 to 0.460 s; n = 12) with a rise time to the maximum amplitude of 0.248 ± 0.043 s (0.177 to 0.330 s; n = 12). The minimum frequency is 3646 ± 553 Hz (2885 to 4694 Hz; n = 12), the peak of dominant frequency is 5233 ± 304 Hz (4823 to 5814 Hz; n = 12), the maximum frequency is 5846 ± 206 Hz (5556 to 6159 Hz; n = 12), and frequency bandwidth is 2200 ± 678 Hz (1162 to 3058 Hz; n = 12). Data on variation of each numerical acoustic property is presented in figure 1. The harmonic structure and call duration of isolated distress calls of L. macrosternum is similar to the distress calls emitted by other leptodactylids, such as L. chaquensis, L. elenae, L. mystacinus, L. labyrinthicus, L. savagei, L. troglodytes and L. vastus (Toledo et al., 2005; Padial et al., 2006; Toledo and Haddad, 2009b; Dourado-Rodrigues et al., 2012). High variation on call duration seems to be a common feature of distress calls in this genus. However, it is the first time that data on the variation of acoustic properties of distress calls are presented. To date, the presence of harmonics is a unanimous feature of the distress call of Neotropical frogs (Toledo and Haddad, 2009b; Lucas R. Forti unpublished data). A detailed comparison of distress calls of Neotropical anurans can be found in Toledo and Haddad (2009b). Generally, the body size may affect some bioacoustic variables, such as call duration (s), intensity (dB) and dominant frequency (Hz) (Toledo and Haddad, 2009b; Santana et al., 2013). However, the influence of body size must still be investigated in leptodactylids taking into account that the distress call of adult L. macrosternum may present acoustic differences, which remains to be studied as well.
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Distress calls of Leptodactylus macrosternum during a cannibal attack This work is a contribution based on a natural history observation that should help on the construction of our general knowledge about feeding habits and defensive repertoire of Neotropical anurans. Acknowledgments. Luís Felipe Toledo provided a critical review on the manuscript, and Simone Dena helped with file deposits in the FNJV. LRF is grateful to the Sao Paulo Research Foundation (FAPESP) for a fellowship (#2013/21519-4), and to the National Council for Scientific and Technological Development (CNPq) for a fellowship (#150041/2017-9).
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Accepted by Iris Starnberger
