Bioacoustics of Eneoptera surinamensis

Redescription. See Robillard & Desutter-Grandcolas (2005) . Calling song. ( Fig. 4D , Table 1 ) Male E. surinamensis call during day time, perched on low vegetation. When several males call together in their natural habitat, and even in laboratory conditions, they usually synchronize amplitude modulations to form a chorus. As previously described by Robillard & Desutter-Grandcolas (2005 , 2011 ) and Miyoshi et al. (2007) , the calling song of E. surinamensis consists of a continuous trill emitted in long bouts that can last a few hours when a male is not disturbed. The call shows a clear amplitude modulation, which generates a regular temporal pattern within the continuous trill, including two distinct sections with different syllables. For the low amplitude sections (ca. 67 syllables), syllables have a duration of 5.4±1.2 ms, and a period of 20.7±4.9 ms. Meanwhile, for the high amplitude sections (ca. 45 syllables), we found that syllable duration is 4.9±1.4 ms, with a shorter period of 17.4±3.1 ms. Thus, the main difference between the low and high amplitude sections is the longer syllable duration and period in the low amplitude sections, while syllables are shorter and closer together in the high amplitude sections. The syllable duty cycles are not clearly different between the two sections (26% for the low amplitude sections, and 28% for high amplitude sections). In terms of frequency, the call shows a low dominant frequency corresponding to the fundamental peak of the spectrum (f1 = 2.95±0.10 kHz). Surprisingly, the spectrum does not show any significant high-frequency component contrary to the prediction of Robillard et al. (2015) , who hypothesized that it might include high-frequencies, as the authors observed in E. guyanensis in the supposedly “low-frequency” section of this species which is emitted by the simple teeth of the stridulatory file. Nevertheless, in E. caliginosa and other non-Lebinthini eneopterines, the call possesses relatively powerful harmonic peaks. Sound-production mechanism. ( Fig 11A , Table 2 ) Males Eneoptera surinamensis possess c. 71 simple teeth arranged along the stridulatory file, as typically observed in crickets. The mean inter-tooth distance, measured for two males , is 35.7 μm in the functional part of the file, with a tooth density of c. 38 teeth/mm. The global speed of stridulation derived from the syllable duration and file length is c. 121 mm /s, which matches the tooth strike rate that generates the fundamental peak of the spectrum.

The teeth of stridulatory file are arranged linearly and inclined from the outer to the inner side of the tegmen (Fig. 1). Each tooth is shell-shaped (Figs. 2, 3); the larger ones are distributed in the medium region of the file, with a gradual reduction in size towards the extremities. The smaller teeth located at the outer (Fig. 4) and inner (Fig. 5) ends of the file show an asymmetric morphology, irregular alignment and intermittent distribution. Parallel to the anterior side of the file occurs a dense accumulation of microtrichias, forming a strip that is broadest where the biggest teeth are located (Figs. 1, 4, 5). There is a gradual reduction in the accumulation of microtrichias following the decrease in teeth size towards the file endings. There are no microtrichias where the smaller, asymmetric and intermittent teeth are located (Figs. 2, 3). Close to the outer end of the file (postcubital area) there is a hair plate (Fig. 1). Specimens from Foz do Iguaçu have a file with 82 ± 9.8 teeth, including the minor and asymmetric ones, with the length of the file equal to 1.89 mm ± 0.15, which is equivalent to 43.76 ± 5.94 teeth per mm. The population from Rio Claro presents a file with 87 ± 9.81 teeth, with 1.96 ± 0.19 mm of length, and 44.52 ± 4.61 teeth per mm. Statistical test had disclosed that the differences found between the two populations are not significant (p>0,05). The specimens from both places had been observed stridulating during the first hours of the morning, at nightfall and during the night. The calling song is a trill that alternates two distinct sets of notes, one of them (section a) with 0.6 s and the other one (section b) with 1.4 s (Fig. 6). The section a includes 46 ± 3.74 (42 - 52, n=5) notes, each note with a duration of 0.009 s; the elapsed time between notes is 0.004 s (Fig. 7). The section b includes 80.8 ± 2.79 (77 - 85, n = 6) notes, with 0.012 s and the elapsed time between them of 0.007 s (Fig. 8). In the section a, each note is composed of 24 pulses and in the section b, of 31 pulses (Figs. 9, 10, respectively). The minimum frequency of the calling song of specimens from Foz do Iguaçu is 2,706.7 ± 97.9 Hz (2497 – 2756, n=7) and the maximum frequency is 3,284.1 ± 153.5 Hz (3,014 – 3,445, n=7). The minimum frequency of the specimen from Rio Claro is 2,325 Hz and the maximum frequency is 3,186 Hz.