Hygrobia hermanni
The call of H. hermanni is biphasic, consisting of two chirps each made up of a ser- ies of pulses (Figure 2). These chirps correspond with the forward and backward stroke of the 7th abdominal ventrite against the pars stridens, respectively (Dettner 1997). Chirp 1 in both sexes shows amplitude modulation which appeared slightly stronger in females. The waveform also reveals that chirp 1 has a higher amplitude and is more distinctly pulsed than chirp 2 (Figure 2). Hygrobia hermanni calls show a broad frequency spectrum, but with some harmonious structure; containing a peak frequency of just over 6 kHz (Figure 2a) in both chirp 1 and chirp 2, this not differing between sexes. A second dominant peak occurs in both sexes at approxi- mately 10.9kHz. Some signal was also visible at higher frequencies, particularly in the first chirp (up to ca. 45 kHz), outside the flat response range of the hydrophone.
The mean duration of a complete call in H. hermanni was 0.746 (±0.038 SE) s in males and 0.656 (±0.035 SE) s in females, these durations not differing significantly (Table 1). Temporal variability was observed across recordings, however, males having longer calls during their final recordings, whereas females were more consist- ent (Table 1; Figure 3). Across recordings, the mean duration of chirp 1 was 0.338 (±0.014 SE) s and 0.322 (± 0.015 SE) s in males and females respectively, but these timings did not differ significantly (Table 1). However, within males, chirp duration did differ significantly across time of recording, being longer during the last recording interval (Table 1; Figure 3). Chirp 2 was shorter than chirp 1 (Figure 2), lasting 0.250 (± 0.018 SE) s in males and 0.209 (±0.018 SE) s in females, although not significantly different between sexes or recordings.
Interval duration differed significantly between sexes, lasting 0.158 (±0.017 SE) s in males and 0.125 (±0.011 SE) s in females (Table 1). Furthermore, interval duration differed over time in both sexes, increasing from first to last recording (Table 1). In females, interval duration increased from 0.112 (±0.016 SE) s to 0.141 (±0.020 SE) s whilst in males it more than doubled, from 0.090 (±0.017 SE) s to 0.233 (±0.037 SE) s (Figure 3). [1]
Viittaukset
The pars stridens of H. hermanni is located on the underside of the elytral apex, being a raised structure containing many small, flattened teeth (Figure 1b–c, f–g). In both sexes, the teeth possess a double-ridge like structure (Figure 1g); each tooth consisting of two ridges separated by a shallow furrow. Stridulatory teeth are struck using the plectrum on the last abdominal ventrite, formed from the flattened apex of the ventrite (Figure 1d–e). Despite differences in ventrite morphology between males and females, plectra appeared identical in their morphologies. The last ventrite is moved rapidly back and forth in an apical to basal direction during sound production in live animals.
Inter-tooth spacing increases apically down the pars stridens in both sexes (Figure 1c–d), but is relatively constant across the central portion of the file (Figure 1c–e). Ridges were the only structures whose size apparently differed between sexes. In females, these are thicker (t 1⁄4 2.81747.884 P1⁄40.023); mean width 8.43 (±0.26 SE) mm compared to 7.34 (±0.29 SE) mm in males. The mean width of individual teeth was 29.93 (±0.47 SE) mm and 28.49 (±1.06 SE) mm in males and females respectively, but these did not differ significantly. The mean length of spac- ing between teeth was 12.10 (±0.98 SE) mm in males and 10.48 (±0.38 SE) mm in females, but again did not differ significantly between sexes. The mean widths of furrows between the two ridges of individual teeth were 14.69 (±0.48 SE) mm in males and 13.78 (±0.72 SE) mm in females, again not significantly different between the sexes. [1]