Aerotegmina vociferator

behaviour · bio.acousti.ca

1. Morphology of the stridulatory file and tegmina The stridulatory file is found on the underside of the left tegmen as it is typical for tettigonioids. On the corresponding vein in the right tegmen no indications of teeth were found (the same situation as in A. kilimandjarica and A. shengenae). In A. vociferator n. sp. and A. megaloptera the file is very long, covered with regularly spaced teeth and strongly elevated (seen from below) above the lower surface of the tegmen. However, both species differ distinctly in file length, tooth number and density (Figure 3; Table 1). The inter-tooth- intervals are largest in the middle part and become slightly smaller towards the ends. There is only a weak basal hump as observed in a much more distinct form in Hexacentrus (see e.g. Heller 1986) and the Hexacentrini-species Nepheliphila raptor (Hugel 2010) (and also in Phlugiolopsis Zeuner, 1940 (Bian et al. 2013)). At the anal/distal end such a small hump can also be recognized, but even weaker than the basal one. The teeth of the file seem to be uniform and do not look like “fused in the middle” (Heller 1995) as in some Pseudophyllinae (see also Montealegre-Z and Morris 1999), although there is a dark band near the middle of the file possibly indicating a change of properties of the cuticula (see Figure 3B, D)). In the stridulatory area of the right tegmen, several relatively large cells can be seen, all quite similar in shape between both species (compare Figures 2 and 4). However, none of these cells is unusually large or has a very transparent (glossy) cuticula (‘mirror’) as is typical for many tettigonioid species. Instead, a large dorsal part of the left tegmen is more transparent (‘semi-transparent’; see Figures 2 and 4) than the rest of the tegmen or the left tegmen. In the smaller Aerotegmina species there is one large, more or less circular, glossy cell (mirror), but some neighbouring areas are also very transparent (Figure 4). 2. Temporal pattern (amplitude modulation) of calling songs Both species were heard singing nearly exclusively at night. Only very occasionally males sang during the daytime, producing regular songs as well as disturbance sounds. The calling songs (Figure 5) consisted of sequences of syllables or groups of syllables with durations up to about one minute. A. megaloptera produced only single, isolated syllables with periods (interval from beginning of a syllable to the beginning of the next) of 1.35 ± 0.6 s (n = 445; median 1.23 s, minimum 0.65 s). In the song of A. vociferator n. sp., single syllables and echemes with up to five syllables were heard. Therefore, the distribution of period lengths had two peaks, one for intra-echeme intervals and one for inter-echeme and single syllable intervals. Intra-echeme periods had a mean of 0.40 ± 0.07 s (n = 338; all periods below 0.5 s), whereas the longer intervals (0.5–10 s) were on average 1.78 ± 0.91 s (n = 781; median 1.56 s). However, the two populations of A. vociferator n. sp. differed in echeme frequency. Mostly single syllables were produced in the Udzungwa population, while echemes occurred at low rate, while echemes were frequent in the Nguru population (see Figure 5). In the rare daytime songs, only single syllables were found. Both species differed distinctly in the duration of the syllables. Syllables of A. megaloptera lasted for 105 ± 11.5 ms (n = 321), while syllables of A. vociferator n. sp. were 214 ± 28 ms (n = 1173) long. However, the values should be treated with caution, since in many record- ings it was quite difficult to define the end of a syllable. There are two main reasons for this problem. First, the amplitude modulation of the syllables is obviously quite variable and even neighbouring syllables can differ distinctly. Sometimes they started soft, distinguishable from noise nearly only in the sonogram, and ended up very loud. If the opposite occurred, echoes may have concealed the true end of syllables. Overall, and corroborated by the few clear recordings (see e.g. Figures 6 and 7), however, it seems safe to state that syllable durations of the two species differ by a factor of about two. The pulses of A. vociferator n. sp. are thus slightly longer than the longest known from crickets (182 ms in Paragryllodes campanella Desutter-Grandcolas, 1998, found also in the East Arc Mountains of Tanzania). Like A. kilimandjarica (Heller et al. 2010), A. vociferator n. sp. produced the sound pulses only during the openingof the tegmina (see Sv1 video). This was confirmed by a frame- to-frame analysis of a video recording, documenting a slow opening and a fast closing movement, much too fast for a long sound pulse. 3. Spectral composition of calling songs Both large Aerotegmina species produced narrow-banded, resonant songs not differing in carrier frequency (A. megaloptera 2031 ± 58 Hz; n = 10 measurements/4 specimens; A. vociferator n. sp. 2058 ± 83 Hz; n = 24/7). The means of individual specimens varied signif- icantly between 1972 and 2225 Hz (ANOVA; F10, 3 = 13.74; p < 0.001). Upper harmonics of the fundamental frequency were present, but quite weak. Our ultrasound equipment was certainly not well-suited to compare their intensity, but also in the recordings with audio microphones the harmonics were at least 30 dB below the peak (Figure 6). To characterize resonant songs, often the Q-factor (Q = quality) is used (e.g. Bennet-Clark 1989). It can be obtained by dividing the peak frequency by the width of the peak 3 dB below the peak (Q3dB). In many pulses of both large Aerotegmina species this width is still within the same spectral line (width 21.53 Hz) as the peak itself and never wider than two lines (see Methods). So Q3dB can be calculated as between >103 and 46–103 (highest and lowest specimen). Within the long pulses of A. vociferator n. sp., the frequency remained not absolutely constant, but changed at maximum by one hundred Hz (5%) as seen in a cycle-by-cycle analysis (Figure 7; 40–50 ms: 2026 Hz; 160–170 ms: 2127 Hz; harmonics removed by band-pass filtering). In recordings of the same animal at different temperatures (21 °C: 2003 ± 17 Hz and 27 °C: 1928 ± 21 Hz; n = 3 each) indications of increasing speed (= higher frequency) with increasing temperature were not seen. 4. Intensity In one male of A. megaloptera, the sound intensity could be determined as 85 ± 2 dB SPL(peak) (n = 6) at 1 m distance, partly measured fronto-dorsally, partly with unknown animal orientation (measurements in Germany under laboratory conditions). In a second series of measurements (another day), the readings were always between 84 and 86 dB SPL(peak), in another orientation only 82–83 dB SPL (peak). Since these values were unex- pectedly low compared to A. kilimandjarica, we took the opportunity to make simultaneous song recordings (sound level meter not available) when again living A. vociferator and kilimandjarica could be obtained. Here, the amplitude of vociferator song had about half of that of kilimandjarica (= 6 dB lower) with both animals at the same distance. However, since below 6 kHz the decrease of the gain of the bat-detector is around 6 dB per octave (estimate by Lars Pettersson, 21.11.2017, pers. communication), both species may have had similar song intensities. The low intensities measured in Germany may have resulted from the age of the animals or other unknown factors.

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