Pectoral sound generation in the blue catfish Ictalurus furcatus

Catfishes produce pectoral stridulatory sounds by “jerk” movements that rub ridges on the dorsal process against the cleithrum. We recorded sound synchronized with high-speed video to investigate the hypothesis that blue catfish Ictalurus furcatus produce sounds by a slip–stick mechanism, previously described only in invertebrates. Blue catfish produce a variably paced series of sound pulses during abduction sweeps (pulsers) although some individuals (sliders) form longer duration sound units (slides) interspersed with pulses. Typical pulser sounds are evoked by short 1–2 ms movements with a rotation of 2°–3°. Jerks excite sounds that increase in amplitude after motion stops, suggesting constructive interference, which decays before the next jerk. Longer contact of the ridges produces a more steady-state sound in slides. Pulse pattern during stridulation is determined by pauses without movement: the spine moves during about 14 % of the abduction sweep in pulsers (~45 % in sliders) although movement appears continuous to the human eye. Spine rotation parameters do not predict pulse amplitude, but amplitude correlates with pause duration suggesting that force between the dorsal process and cleithrum increases with longer pauses. Sound production, stimulated by a series of rapid movements that set the pectoral girdle into resonance, is caused by a slip–stick mechanism

MORPHOLOGY, MATERIAL AND VIBRATORY PROPERTIES OF THE SWIMBLADDER IN THE CARP, CYPRINUS CARPIO

The carp Cyprinus carpio has a two-chambered swimbladder and excellent hearing. I explored the hypothesis that the anterior chamber, which connects to Weberian ossicles, is adapted for hearing by testing both chambers for material properties. I also determined displacement and auditory responses to mechanical strikes. Wall stress is higher in the posterior, strain in the anterior and modulus lower in the anterior chamber. Strikes increase pressure followed by a variable rebound that rapidly decays. Displacement and sound amplitude increase with hammer force, and amplitude is similar in both chambers for within chamber strikes but lower across chambers. Normalized for equivalent displacement, the anterior chamber produces a more intense sound. Stiffness and damping are greater for the anterior chamber, but sound spectra are similar. More intense sound production per unit of movement, greater damping and higher stiffness for the anterior chamber should all contribute to high-frequency auditory sensitivity

Characterization and Generation of Male Courtship Song in Cotesia congregata (Hymenoptera: Braconidae)

Background Male parasitic wasps attract females with a courtship song produced by rapid wing fanning. Songs have been described for several parasitic wasp species; however, beyond association with wing fanning, the mechanism of sound generation has not been examined. We characterized the male courtship song of Cotesia congregata (Hymenoptera: Braconidae) and investigated the biomechanics of sound production. Methods and Principal Findings Courtship songs were recorded using high-speed videography (2,000 fps) and audio recordings. The song consists of a long duration amplitude-modulated “buzz” followed by a series of pulsatile higher amplitude “boings,” each decaying into a terminal buzz followed by a short inter-boing pause while wings are stationary. Boings have higher amplitude and lower frequency than buzz components. The lower frequency of the boing sound is due to greater wing displacement. The power spectrum is a harmonic series dominated by wing repetition rate ~220 Hz, but the sound waveform indicates a higher frequency resonance ~5 kHz. Sound is not generated by the wings contacting each other, the substrate, or the abdomen. The abdomen is elevated during the first several wing cycles of the boing, but its position is unrelated to sound amplitude. Unlike most sounds generated by volume velocity, the boing is generated at the termination of the wing down stroke when displacement is maximal and wing velocity is zero. Calculation indicates a low Reynolds number of ~1000. Conclusions and Significance Acoustic pressure is proportional to velocity for typical sound sources. Our finding that the boing sound was generated at maximal wing displacement coincident with cessation of wing motion indicates that it is caused by acceleration of the wing tips, consistent with a dipole source. The low Reynolds number requires a high wing flap rate for flight and predisposes wings of small insects for sound production

Oscillograph of typical male courtship song of <i>Cotesia congregata</i> with a buzz followed by boings.

<p>(A) Complete song. (B) Expanded selection of initial buzz. (C) Expanded selection of four boings illustrating the initial high amplitude component followed by a lower amplitude terminal buzz and short gap.</p

Images of a single wing stroke during a boing matched to sound amplitude.

<p><b>Above:</b> High-speed camera photographs (2,000 fps) of one wing cycle during a boing produced by downward (a–e) and upward (f–j) wing movement from a male <i>Cotesia congregata</i> displaying to an immobilized female. Each image represents 0.5 ms. Note that wings are less clear in the middle of the down and upsweep (images b–d and g–i) due to rapid movement. <b>Below:</b> Oscillograph of one cycle of a boing with wing positions in a-j keyed to time of occurrence.</p

Sound pressure level and fundamental frequency of the male courtship song of <i>Cotesia congregata</i>.

<p>(A) Sound pressure level re: 20 µPa at 2–3 mm (dB; mean ± SE) and (B) fundamental frequency (Hz; mean ± SE) of initial pre-boing buzz, boing, and terminal buzz components. Different letters indicate significant differences (p<0.01). <i>N</i> = 21 wasps.</p

Frequency spectra of components of the male courtship song of <i>Cotesia congregata</i>.

<p>(A) Boing, (B) terminal buzz, and (C) background noise.</p

Change in wing angle over time during a single boing.

<p>Vertical wing angle at the beginning and end of successive wing strokes during a typical boing (vertical plane toward the substrate = 0°) of the male courtship song of <i>Cotesia congregata</i>. The first arrow indicates the first wing stroke producing audible sound and the second arrow indicates the downstroke producing the highest amplitude sound.</p

Measurements of wasp movement and sound amplitude of each wing stroke during a single boing.

<p>(A) Wing downstroke displacement (mean ± SE), (B) maximum downstroke velocity, (C) abdominal angle (horizontal = 0°), and (D) sound amplitude during successive wing strokes during a boing averaged from frame by frame analysis of the courtship song produced by three males of <i>Cotesia congregata</i>. Strokes from boings with more than 14 pulses were deleted so that <i>N</i> was always 3.</p

Dorsal view of one pair of wings of a male <i>Cotesia congregata</i>.

<p>The wings are supported by a microscope slide (vertical line near the wing base). The terminal fold used in calculations of wing speed is indicated by the arrow.</p