Herpetology Notes, volume 11: 819-823 (2018) (published online on 27 September 2018) The amplectant and aggressive calls and notes on the reproductive behaviour of the Porthole Frog (Charadrahyla taeniopus) José M. Serrano1,2,* Abstract. The behavioural context at which reproductive calls, other than advertisement call, are performed by anurans has been rarely studied in depth. Herein I describe in detail the vocalization behaviour of a frog whose voice was enigmatic until now. Amplectant and aggressive calls of the porthole frog Charadrahyla taeniopus (Günther, 1901) are described showing their differences in temporal and spectral characteristics. The number of produced calls from each type fluctuated in an alternate pattern over the 28 minutes recorded. Although some signal of assortative mating was detected in the pair size correlation test, no statistical differences were detected between the body size of amplectant and by-stander males. Keywords. Anuran communication, sounds repertoire, fluctuating behaviour, stream breeder frog Introduction 1980; Bowcock et al., 2008), and are of potential interest for the evolution of anuran communication (Schmidt et Anurans rely on acoustic signals for communicating al., 1990). in diverse contexts. After the pioneering publication Stream frogs have adapted their calling behaviour to of Bogert (1960), vocal signals of anurans are usually overcome the running water noise, by emitting high- referred to as calls and traditionally defined in relation frequency harmonics in their vocalizations, some to the context in which they are produced (Wells, 1977; reaching the ultrasonic domain (Dubois and Martens, Wells and Schwartz, 2007). More recently Toledo et al. 1984; Narins et al., 2004, Vargas-Salinas et al., 2014), (2014) defined anuran call types and pointed out that a or displaying visual cues (Preininger et al., 2013) to correct classification of calls is a complex task in many communicate with conspecifics. Alternatively, some cases, particularly when these are highly variable or low stream species like Rhinella arunco and Rhinella occur in different contexts; e.g., aggressive calls (Greer and Wells, 1980). Female-attracting advertisement spinulosa do not produce advertisement calls but calls produced by males are by far the most studied amplectant calls (Penna and Veloso, 1981). Some vocalization in frogs (Wells and Schwartz, 2007), stream-dwelling species exhibit vocal sacs but their while other acoustic signals also produced in mating advertisement calls have never been recorded and only contexts like aggressive and amplectant calls remain increased fieldwork could to resolve whether these frogs understudied. By instance, amplectant calls have been produce low amplitude and sporadic sounds or have rarely reported in anurans (Toledo et al., 2014; Köhler evolved true voiceless (Emerson and Berrigan, 1993). et al., 2017), although they are continually performed by The genus Charadrahyla is a group of stream frogs some species during long reproductive clasps (Picker, distributed in tropical southern Mexico. Males of some species from the genus form chorus where callers and non-callers get involved in scramble competition for the acquisition of mates (Duellman, 2001). Males and females of the porthole frog C. taeniopus are usually 1 Posgrado, Instituto de Ecología A.C., Xalapa, Veracruz, found between canopy vegetation of cloud forests near México. to permanent and generally quiet streams. The species 2 Present address: Programa de Fisiología y Biofísica, Facultad de Medicina, Universidad de Chile, Independencia 1027, has sexually dimorphic colour and body shape patterns 8380453, Independencia, Santiago, Chile. (Duellman, 2001). The female dorsum is reddish, while * Author e-mail: [email protected] the dorsum of males is yellow-green bright, and their 820 José M. Serrano Materials and Methods A breeding aggregation of C. taeniopus located in a region of cloud forest in Central Veracruz, Mexico, known as “El Riscal” (19.4822°N, 96.9978°W; 1600 m altitude) on the night of 26 November 2007 was found during the search for the syntopic species Rheohyla miotympanum. The area of the perennial stream where the group of callers was located was low flowing and silent, with pools having a maximum 0.5 m deep and 1.5 m wide, muddy bottom, submerged leaf litters and some algae. The vocal activity was recorded with a digital recorder Olympus DS30 (built-in stereo microphone, 44 kHz sampling rate, 16-bit resolution) was positioned from ~ 50 cm above the centre of the calling group with an arm stand. To avoid interrupting reproductive and aggressive interactions focal recordings of closely calling individuals were not attempted. Detailed descriptions of the behaviour observed were dictated onto the recording. After recording the vocalizations, snout-vent length (SVL) of amplectant pairs and unpaired males were measured using a calliper (error = 0.1 mm). Acoustic analysis of isolated, non-overlapping calls in the recordings was carried out using Sound Ruler 0.9.6.0 software (Gridi-Papp, 2007). Call duration, note duration, and inter-note interval duration were measured from oscillograms and the dominant frequency was measured using the automated mode employing the Figure 1. Photographs of the porthole frog Chraradrahyla Hamming window and FFT with 1060 samples. The taeniopus showing: A) a couple of male and female in context in which calls were produced and the difference amplexus; B) the breeding aggregation during scramble observed in their acoustic properties were used to competition behaviour. define the types of calls based on Köhler et al. (2017). The number of the different type of calls observed was counted using two-minute bins. The relationship among the sizes of males and females snouts are narrow and pointed relative to females (Fig in amplexus was estimated to evaluate the occurrence of 1A). The mating season of C. taeniopus extends from size-assortative mating. Spearman correlation index was late fall to mid-winter (Duellman, 2001), corresponding applied with this purpose due to the small number of to the period of cold rains known as “nortes,” originated pairs observed. Body sizes of amplectant and unpaired in the Gulf of Mexico (Williams-Linera, 2007). Eggs males were compared with the non-parametrical U- are laid in streams, where tadpoles probably develop Mann-Whitney test. All statistics were performed using until the following summer or fall (Duellman, 2001). R statistical software v.3.0.2 (http://www.r-project. Charadrahyla taeniopus has not been observed to org). vocalize in the wild, despite having bilateral vocal slits (Duellman, 2001). The main purpose of this manuscript Results is to describe for the first time the calling behaviour and acoustic emissions of C. taeniopus, including the A group formed by 32 males and 11 females of C. temporary sequence of exchange for two types of calls. taeniopus was observed spread over two meters along Additionally, data on the size of amplectant individuals the stream. This group was detected by the scramble was used to evaluate whether size-assortative mating noise of calls and repeated jumps on water. The vocal might be occurring in this species. activity of the group was recorded for 28 minutes, The amplectant and aggressive calls of the Porthole Frog 821 Figure 2. Oscillogram, spectrogram and power spectra of amplectant and aggressive calls of Charadrahyla taeniopus. A) Representative amplectant call consisting of a series of three notes composed by two pulse groups, the power spectrum corresponds to the double pulse of the first note. B) Representative aggressive call, the power spectrum corresponds to the second note. starting at 22:45 h. Two different types of calls were physical contact with other males during scrambling produced by males of C. taeniopus in different social competition and in attempts to displace other males contexts during a breeding aggregation and these from amplexus (Fig. 1B). The vocal sacs did not were clearly distinguishable in spectrograms and inflate markedly during the broadcast of both types of oscillograms. Amplectant calls were emitted by males calls, rather than that, remarkable muscular thoracic holding a female in amplexus (Fig. 1A). Vocalizations contractions in direct contact with the female dorsum referred as aggressive calls were produced by males in were observed. 822 José M. Serrano Table 1. Acoustic characteristics of amplectant and aggressive calls produced by a group of Charadrahyla taeniopus males in a Table 1. Acoustic characteristics of amplectant and aggressive calls produced by a group of Charadrahyla taeniopus breeding aggregation.males Abbreviations: in a breeding aggregation. DF= dominant Abbreviations: frequency, DF= CD= dominant call frequency,duration, ND=CD= call note duration, duration, ND= IN= note inter duration, note interval duration, NN= numberIN= inter of notes.note interval Averages duration, with NN= ranges number in parenthesis of notes. Averages are shown. with ranges in parenthesis are shown. Call type DF (Hz) CD (s) ND (ms) IN (s) NN Amplectant 1707 2.21 10.85 0.19 5.3 (n= 358) (692 – 2670) (0.05–11.82) (0.66 –31.68) (0.03 – 0.38) (1 – 31) Aggressive 1436 0.45 18.64 0.08 5.5 (n= 320) (775 – 2497) (0.107–1.19) (1.92 – 37.57) (0.04 – 0.25) (1 – 13) Acoustic characteristics of amplectant and aggressive high motor activity in which males struggled and calls produced by C. taeniopus are listed in Table 1. jumped restlessly. The air temperature measured at the Amplectant calls (N= 358) included bouts of notes (1 beginning of the recording period was 15.6° C, and – 31) containing (5 – 7) harmonics, with a dominant relative humidity measured at five cm above the stream frequency (692 – 2670 Hz) corresponding to the first surface was 92.5%. These environmental conditions to third harmonic. The notes were formed by one to remained constant throughout the recording period. three pulses, the first pulse formed typically by lower All 11 females observed in the group were clasped by amplitude than the following (Fig. 2A). Aggressive males.