Biomedical subjects

P A Faure

Publications and source records attributed to P A Faure.

6 recordsLinked to original sources

PubMed2000

The sounds of silence: cessation of singing and song pausing are ultrasound-induced acoustic startle behaviors in the katydid Neoconocephalus ensiger (Orthoptera; Tettigoniidae).

Previous studies of acoustic startle in insects have dealt with behavioral and/or neural mechanisms employed in evading aerially hawking, echolocating bats; however, insects also face terrestrial predators. Here we describe an acoustic startle response of the nocturnal katydid, Neoconocephalus ensiger. Stridulating males disturbed in the field perform obvious antipredatory behaviors--cessation of singing, freezing, jumping, and evasive flight. Under controlled laboratory conditions we found that cessation of singing and song pausing are ultrasound-specific behaviors: when stimulated with pulsed ultrasound (20-100 kHz), but not audio-sound (< 20 kHz), males cease mate calling or insert pauses in their song. A second factor influencing acoustic startle is the phase of stimulation: an acoustic startle response occurs only when the pulse of ultrasound arrives during the window of silence between stridulatory syllables. The average startle threshold and response latency was 70 +/- 5 dB SPL and 34.2 +/- 6.0 ms, respectively. N. ensiger is particularly useful for examining acoustic startle responses of nonflying insects because (1) its calling song is broadband and contains ultrasound, thus the possibility exists of confusion over the biological meaning of ultrasound, and (2) this species shows the classic bat-avoidance response while flying, so a direct comparison between two types of acoustic startle is possible within the same species.

Acoustic Stimulation↗

PubMed2000

Auditory symmetry analysis.

The study of biological symmetry continues to be an important and active area of research, yet in the hearing sciences there are no established quantitative methods for measuring auditory asymmetries and dissimilarities in threshold tuning curves (i.e. audiograms). Using a paired design and adopting methods from the analysis of fluctuating asymmetry, we describe methods for auditory researchers interested in delineating auditory asymmetries and comparing tuning curves, behavioral or neural. We illustrate the methods using audiograms of the prothoracic T-cell interneuron in a nocturnal katydid (Neoconocephalus ensiger). The results show that 87-92 % of T-cells had right-minus-left threshold asymmetries no larger than expected from measurement error alone. Thus, apart from small random fluctuating asymmetries, T-cell pairs in N. ensiger showed no sensory bias and were bilaterally symmetrical from 5 to 100 kHz. The sensitivity of the methods for detecting tuning curve dissimilarities was confirmed in a sound lateralization paradigm by comparing the 'symmetry' (i.e. similarity) of T-cell tuning curves measured at 0 degrees stimulation with tuning curves measured at 90 degrees stimulation for the same T-cell. The results show that T-cell thresholds measured frontally (0 degrees ) were significantly higher than those measured laterally (90 degrees ), particularly for ultrasonic frequencies. Statistically, the directional shift (increase) in auditory thresholds was detected as a directional asymmetry in T-cell tuning, whose origin and functional significance to an insect behaving normally are discussed. The paper discusses practical considerations for detecting auditory asymmetries and tuning curve dissimilarities in general, and closes by questioning the relevance of auditory symmetry for sound localization in both vertebrates and insects.

Animals↗

PubMed2000

Neuroethology of the katydid T-cell. I. Tuning and responses to pure tones.

The tuning and pure-tone physiology of the T-cell prothoracic auditory interneuron were investigated in the nocturnal katydid Neoconocephalus ensiger. The T-cell is extremely sensitive and broadly tuned, particularly to high-frequency ultrasound (>20 kHz). Adult thresholds were lowest and showed their least variability for frequencies ranging from 25 to 80 kHz. The average best threshold of the T-cell in N. ensiger ranged from 28 to 38 dB SPL and the best frequency from 20 to 27 kHz. In females, the T-cell is slightly more sensitive to the range of frequencies encompassing the spectrum of male song. Tuning of the T-cell in non-volant nymphs was comparable with that of adults, and this precocious ultrasound sensitivity supports the view that it has a role in the detection of terrestrial sources of predaceous ultrasound. In adults, T-cell tuning is narrower than that of the whole auditory (tympanic) organ, but only at audio frequencies. Superthreshold physiological experiments revealed that T-cell responses were ultrasound-biased, with intensity/response functions steeper and spike latencies shorter at 20, 30 and 40 kHz than at 5, 10 and 15 kHz. The same was also true for T-cell stimulation at 90 degrees compared with stimulation at 0 degrees within a frequency, which supports early T-cell research showing that excitation of the contralateral ear inhibits ipsilateral T-cell responses. In a temporal summation experiment, the integration time of the T-cell at 40 kHz (integration time constant tau =6.1 ms) was less than half that measured at 15 kHz ( tau =15.0 ms). Moreover, T-cell spiking in response to short-duration pure-tone trains mimicking calling conspecifics (15 kHz) and bat echolocation hunting sequences (40 kHz) revealed that temporal pattern-copying was superior for ultrasonic stimulation. Apparently, T-cell responses are reduced or inhibited by stimulation with audio frequencies, which leads to the prediction that the T-cell will encode conspecific song less well than bat-like frequency-modulated sweeps during acoustic playback. The fact that the T-cell is one of the most sensitive ultrasound neurons in tympanate insects is most consistent with it serving an alarm, warning or escape function in both volant and non-volant katydids (nymphs and adults).

Acoustic Stimulation↗

PubMed2000

Neuroethology of the katydid T-cell. II. Responses to acoustic playback of conspecific and predatory signals.

Although early work on the tettigoniid T large fiber suggested that it might mediate early-warning and escape behavior in katydids, the majority of research thereafter has focused on the ability of the T-cell to detect, localize and/or discriminate mate-calling song. Interestingly, T-cell responses to conspecific song are rarely examined for more than a few seconds, despite the fact that many katydids sing for minutes or hours at a time. In this paper, the second of a pair examining the physiology of the T-cell in Neoconocephalus ensiger, we recorded T-cell responses using longer-duration playbacks (3 min) of conspecific song (Katydid signal 30 ms syllables, 9-25 kHz bandwidth, 12-15 kHz peak frequency) and two types of bat-like ultrasound, a 10 ms, 80->30 kHz frequency-modulated sweep (Bat 10 signal) and a 30 ms, 80->30 kHz frequency-modulated sweep (Bat 30 signal). Spiking responses were distinctly biased towards the short-duration ultrasonic signal, with more spikes per pulse, at a shorter spike latency and at a higher instantaneous firing frequency to the Bat 10 signal than to the Katydid signal or, surprisingly, to the Bat 30 signal. The ability of the T-cell to encode the temporal pattern of the stimulus was particularly striking. Only for the predatory bat signals did T-cell spiking faithfully copy the stimulus; playbacks of conspecific song resulted in significantly weaker spiking responses, particularly in male katydids. The results demonstrate that responses from the T-cell alone may be sufficient for katydids to discriminate biologically relevant signals pertinent to the phonotactic behavior patterns involved in mate attraction and predator avoidance.

Acoustic Stimulation↗

PubMed1994

Substrate-gleaning versus aerial-hawking: plasticity in the foraging and echolocation behaviour of the long-eared bat, Myotis evotis.

The foraging and echolocation behaviour of Myotis evotis was investigated during substrate-gleaning and aerial-hawking attacks. Bats gleaned moths from both the ground and a bark-covered trellis, however, they were equally adept at capturing flying moths. The calls emitted by M. evotis during substrate-gleaning sequences were short, broadband, and frequency-modulated (FM). Three behavioural phases were identified: search, hover, and attack. Gleaning search calls were significantly longer in duration, lower in highest frequency, and larger in bandwidth than hover/attack calls. Calls were detected in only 68% of gleaning sequences, and when they were emitted, bats ceased calling approximately 200 ms before attacking. Terminal feeding buzzes, the rapid increase in pulse repetition rate associated with an attempted prey capture, were never recorded during gleaning attacks. The echolocation calls uttered by M. evotis during aerial-hawking foraging sequences were also short duration, high frequency, FM calls. Two distinct acoustic phases were identified: approach and terminal. Approach calls were significantly different from terminal calls in all variables measured. Calls were detected in 100% of aerial-hawking attacks and terminal feeding buzzes were invariably produced. Gleaning hover/attack calls were spectrally similar to aerial approach calls, but were shorter in duration and emitted at a significantly lower (but constant) repetition rate than aerial signals. Although the foraging environment (flight cage contents) remained unchanged between tasks (substrate-gleaning vs. aerial-hawking), bats emitted significantly lower amplitude calls while gleaning. We conclude that M. evotis adjusts its echolocation behaviour to meet the perceptual demands (acoustical constraints) imposed by each foraging situation.

Animals↗

PubMed1993

The gleaning attacks of the northern long-eared bat, Myotis septentrionalis, are relatively inaudible to moths.

This study empirically tests the prediction that the echolocation calls of gleaning insectivorous bats (short duration, high frequency, low intensity) are acoustically mismatched to the ears of noctuid moths and are less detectable than those of aerially hawking bats. We recorded auditory receptor cell action potentials elicited in underwing moths (Catocala spp.) by echolocation calls emitted during gleaning attacks by Myotis septentrionalis (the northern long-eared bat) and during flights by the aerial hawker Myotis lucifugus (the little brown bat). The moth ear responds inconsistently and with fewer action potentials to the echolocation calls emitted by the gleaner, a situation that worsened when the moth's ear was covered by its wing (mimicking a moth resting on a surface). Calls emitted by the aerial-hawking bat elicited a significantly stronger spiking response from the moth ear. Moths with their ears covered by their wings maintained their relative hearing sensitivity at their best frequency range, the range used by most aerial insectivorous bats, but showed a pronounced deafness in the frequency range typically employed by gleaning bats. Our results (1) support the prediction that the echolocation calls of gleaners are acoustically inconspicuous to the ears of moths (and presumably other nocturnal tympanate insects), leaving the moths particularly vulnerable to predation, and (2) suggest that gleaners gain a foraging advantage against eared prey.

Acoustics↗