Acinipe segurensis

Description of structures involved in sound production
The structures involved in sound production are tegmina and wings. The tegmen is a lobe form, like a spatula, narrow and uniformly coloured. Its upper (dorsal) edge is almost straight and its apex is more or less rounded. On its inner side, there is a marked longitudinal ridge, located approximately in the proximal third (Figure 1). The wing is rudimentary (Figure 1), formed by an irregular rectangular lobe (1.8 × 0.6 mm in a living specimen) attached to the corpse by its inner margin and with its costal edge free, ventrally directed when in rest. The wing can be raised out of the body to a nearly horizontal plane.

Sound production
Sound produced by females when isolated from males has been the only registered sound under natural conditions. Females started to sing about 10–15 days after the last moult. Males never produced song, despite the fact that their tegmen and wing structure are similar to that of females, and when handled it is able to produce sounds that are similar to those of females.
Concerning sound production, it was observed that just before beginning of a song, the specimen contracts its body and then moves the tegmina away from and near to the body, without displacing them in the plane. This movement caused by the tegmina appears to hit the abdomen laterally. When the tap- ping finished, the abdomen relaxed.

Sound description
The song is composed of isolated echemes produced sporadically. No periodicity was observed. Echemes lasted 0.50 ± 0.12 s and were formed by seven syllables as a mean (min. four, max. 13). Syllables, lasting 0.008 ± 0.002 s, were emitted at a rate of 14.26 ± 4.76 syl/s.
In 55% of the recorded songs, the echeme is formed by single syllables (Figure 2). In 40%, sylla- bles are composed of two hemisyllables (Figure 3), both weak and loud, with the weakest one usually losing intensity as the echeme progresses. Echemes can start with either one weak hemisyllable (46.7%) or not (53.3%), thus making the starting syllable either double or single. In about 5% of the recorded songs, there were single and double syllables mixed, in addition to the starting syllable.
In 47% of the recorded songs, both loud and weak asynchronies in the syllables produced were observed (Figure 3). This is most likely due to imperfect synchronization in the movement of the tegmina during the song, as in Glauia durieui (Bolívar, 1878) (Johnsen 1972). Asynchronies are more evident and frequent in the first syllables of an echeme. In only one case, the echeme started synchronically and finished with asynchronic
Figure 2. Spontaneous song of Acinipe segurensis. a: with double syllables; b: with single syllables.
syllables. About 94% of asynchronic songs are com- posed of double syllables.
As concerns the frequency domain, the results show that the sound occupies a relatively wide band (8200 ± 2300 Hz), with the minimum frequency being around 2000 Hz and the maximum frequency at around 10,200 Hz. The frequency spectrum shows a “double wave” appearance, with the main peak at around 4000 Hz and a second one close to 8000 Hz (Figure 4a). When loud and weak hemisyllables are analyzed separately, the frequency spectrum offers similar results. However, the main peak shows differ- ences because while the main peak of the loud syllable matches the first one (around 4000 Hz), the main peak of the weak syllable matches the second one (around 8000 Kz) (Figure 4b and c).
As indicated in the Materials and methods, two different experiments were carried out to verify the structures involved in sound production by artificial handling of the wing and tegmen. Although the record- ings that were obtained did not usually offer a very good signal/noise ratio, they could be studied in the frequency domain. The resultant frequency spectrum was comparable to that of the spontaneous songs in the two different experiments (Figure 5a and b). When two hemisyllables were produced (Figure 6a), the main peak of frequency spectra of the loud and weak ones fit that of spontaneous loud and weak syllables, respec- tively (Figure 6b and c), thus suggesting that all sounds were produced by the same structures. In summary, the relation of tegmen and wing in sound production appears clear. [1]

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