@article {57966, title = {The Cercal Organ May Provide Singing Tettigoniids a Backup Sensory System for the Detection of Eavesdropping Bats}, year = {2010}, abstract = {

Conspicuous signals, such as the calling songs of tettigoniids, are intended to attract mates but may also unintentionally attract predators. Among them bats that listen to prey-generated sounds constitute a predation pressure for many acoustically communicating insects as well as frogs. As an adaptation to protect against bat predation many insect species evolved auditory sensitivity to bat-emitted echolocation signals. Recently, the European mouse-eared bat species Myotis myotis and M. blythii oxygnathus were found to eavesdrop on calling songs of the tettigoniid Tettigonia cantans. These gleaning bats emit rather faint echolocation signals when approaching prey and singing insects may have difficulty detecting acoustic predator-related signals. The aim of this study was to determine (1) if loud self-generated sound produced by European tettigoniids impairs the detection of pulsed ultrasound and (2) if wind-sensors on the cercal organ function as a sensory backup system for bat detection in tettigoniids. We addressed these questions by combining a behavioral approach to study the response of two European tettigoniid species to pulsed ultrasound, together with an electrophysiological approach to record the activity of wind-sensitive interneurons during real attacks of the European mouse-eared bat species Myotis myotis. Results showed that singing T. cantans males did not respond to sequences of ultrasound pulses, whereas singing T. viridissima did respond with predominantly brief song pauses when ultrasound pulses fell into silent intervals or were coincident with the production of soft hemi-syllables. This result, however, strongly depended on ambient temperature with a lower probability for song interruption observable at 21uC compared to 28uC. Using extracellular recordings, dorsal giant interneurons of tettigoniids were shown to fire regular bursts in response to attacking bats. Between the first response of wind-sensitive interneurons and contact, a mean time lag of 860 ms was found. This time interval corresponds to a bat-to-prey distance of ca. 72 cm. This result demonstrates the efficiency of the cercal system of tettigoniids in detecting attacking bats and suggests this sensory system to be particularly valuable for singing insects that are targeted by eavesdropping bats.

}, doi = {10.1371/journal.pone.0012698}, url = {https://dx.plos.org/10.1371/journal.pone.0012698}, author = {Hartbauer, Manfred and Ofner, Elisabeth and Grossauer, Viktoria and Siemers, Bj{\"o}rn M.}, editor = {Borst, Alexander} } @article {57650, title = {Matched Filters, Mate Choice and the Evolution of Sexually Selected Traits}, year = {2008}, abstract = {

Background: Fundamental for understanding the evolution of communication systems is both the variation in a signal and how this affects the behavior of receivers, as well as variation in preference functions of receivers, and how this affects the variability of the signal. However, individual differences in female preference functions and their proximate causation have rarely been studied.

Methodology/Principal Findings: Calling songs of male field crickets represent secondary sexual characters and are subject to sexual selection by female choice. Following predictions from the \‘\‘matched filter hypothesis\’\’ we studied the tuning of an identified interneuron in a field cricket, known for its function in phonotaxis, and correlated this with the preference of the same females in two-choice trials. Females vary in their neuronal frequency tuning, which strongly predicts the preference in a choice situation between two songs differing in carrier frequency. A second \‘\‘matched filter\’\’ exists in directional hearing, where reliable cues for sound localization occur only in a narrow frequency range. There is a strong correlation between the directional tuning and the behavioural preference in no-choice tests. This second \‘\‘matched filter\’\’ also varies widely in females, and surprisingly, differs on average by 400 Hz from the neuronal frequency tuning.

Conclusions/Significance: Our findings on the mismatch of the two \‘\‘matched filters\’\’ would suggest that the difference in these two filters appears to be caused by their evolutionary history, and the different trade-offs which exist between sound emission, transmission and detection, as well as directional hearing under specific ecological settings. The mismatched filter situation may ultimately explain the maintenance of considerable variation in the carrier frequency of the male signal despite stabilizing selection.

}, doi = {10.1371/journal.pone.000300510.1371/journal.pone.0003005.g00110.1371/journal.pone.0003005.g00210.1371/journal.pone.0003005.g00310.1371/journal.pone.0003005.g00410.1371/journal.pone.0003005.t001}, url = {https://dx.plos.org/10.1371/journal.pone.0003005}, author = {Kostarakos, Konstantinos and Hartbauer, Manfred and Heiner R{\"o}mer}, editor = {Tregenza, Tom} } @article {50906, title = {The heterospecific calling song can improve conspecific signal detection in a bushcricket species}, journal = {Hearing Research}, year = {2017}, month = {Jan-09-2017}, abstract = {

In forest clearings of the Malaysian rainforest, chirping and trilling Mecopoda species often live in sympatry. We investigated whether a phenomenon known as stochastic resonance (SR) improved the ability of individuals to detect a low-frequent signal component typical of chirps when members of the heterospecific trilling species were simultaneously active. This phenomenon may explain the fact that the chirping species upholds entrainment to the conspecific song in the presence of the trill. Therefore, we evaluated the response probability of an ascending auditory neuron (TN-1) in individuals of the chirping Mecopoda species to triple-pulsed 2, 8 and 20 kHz signals that were broadcast 1 dB below the hearing threshold while increasing the intensity of either white noise or a typical triller song.

Our results demonstrate the existence of SR over a rather broad range of signal-to-noise ratios (SNRs) of input signals when periodic 2 kHz and 20 kHz signals were presented at the same time as white noise. Using the chirp-specific 2 kHz signal as a stimulus, the maximum TN-1 response probability frequently exceeded the 50\% threshold if the trill was broadcast simultaneously. Playback of an 8 kHz signal, a common frequency band component of the trill, yielded a similar result. Nevertheless, using the trill as a masker, the signal-related TN-1 spiking probability was rather variable. The variability on an individual level resulted from correlations between the phase relationship of the signal and syllables of the trill. For the first time, these results demonstrate the existence of SR in acoustically-communicating insects and suggest that the calling song of heterospecifics may facilitate the detection of a subthreshold signal component in certain situations. The results of the simulation of sound propagation in a computer model suggest a wide range of sender-receiver distances in which the triller can help to improve the detection of subthreshold signals in the chirping species.

}, keywords = {acoustic communication, auditory interneuron, Ensifera, signal detection, stochastic resonance}, issn = {03785955}, doi = {10.1016/j.heares.2017.09.011}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0378595517302113}, author = {Abdelatti, Zainab A.S. and Hartbauer, Manfred} }