A complex mechanism of call recognition in the katydid Neoconocephalus affinis (Orthoptera: Tettigoniidae)

Abstract

SUMMARYAcoustic pattern recognition is important for bringing together males and females in many insect species. We used phonotaxis experiments on a walking compensator to study call recognition in the katydid Neoconocephalus affinis, a species with a doublepulsed call and an atypically slow pulse rate for the genus. Call recognition in this species is unusual because females require the presence of two alternating pulse amplitudes in the signal. A Fourier analysis of the stimulus-envelopes revealed that females respond only when both the first and second harmonics of the AM spectrum are of similar amplitude. The second harmonic is generated by the amplitude difference between the two pulses making up a pulse-pair. Females respond to double pulses that have been merged into a single pulse only if this amplitude modulation is preserved. Further experiments suggest that females use a resonance mechanism to recognize the pulse rate of the call, supporting a neural model of rate recognition in which periodic oscillations in membrane potential are used to filter the pulse rate of the signal. Our results illustrate how a reduction in pulse rate extends the opportunities for females to evaluate fine-scale temporal properties of calls, and provide further evidence for the importance of oscillatory membrane properties in temporal processing. The results are discussed with regard to evolutionary changes in call recognition mechanisms within the genus.

Character State Reconstruction of Call Diversity in the Neoconocephalus Katydids Reveals High Levels of Convergence

“…These slow amplitude modulations (AM) are important for female preferences in N. affinis and N. ensiger 26 , 42; N. retusiformis calls have a distinct slow AM rate, but we lack data on female preferences. Male N. exciliscanorus typically have seven opening and closing movements in each chirp22.…”

“…Neoconocephalus calls are produced during opening and closing of the forewings (elytra); loud sound pulses are produced during the closing, while sounds during the opening are typically much softer22 and are not required for female responses (e.g 1718 , 24 , 25; but see 26). We therefore limit our description of the temporal pattern to the closing pulses and refer to them simply as 'pulses.'…”

“…(see text); * the verse duration for N. ensiger as given here interprets individual pulses as chirps (see text).SpeciesCall StructureVerse DurationVerse Rate[Hz]Pulse PatternPulse Rate[Hz]SourceN. affinisC--doubleslow 10-12 15 26 N. bivocatusC--doublefast 155-175 17 39 N.…”

“…15 , 16 , 17 , 18), call mechanics19 , 20 , 21 , 22, female preferences (e.g. 23 , 24 , 25 , 26), and sensory processing (e.g. 27 , 28 , 29 , 30 , 31).…”

Application of insect songs in monitoring population density level of Locusta migratoria migratoria (Orthoptera: Acrididae)

“…The second harmonic is generated by the amplitude difference between the two pulses making up a pulse pair. Females respond to double pulses that have been merged into a single pulse only if this amplitude modulation is preserved (Bush et al 2009). Insect songs had a good stability that is already used as a powerful tool in taxonomy, especially in some closerelated species (Schul 1998).…”