Department of Zoology, Karl-Franzens Universität, Graz, Austria.
PLoS One. 2010 Sep 13;5(9):e12698. doi: 10.1371/journal.pone.0012698.
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 21°C compared to 28°C. 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.
明显的信号，如螽斯的求偶叫声，旨在吸引配偶，但也可能无意中吸引捕食者。其中，以猎物发出的声音为食的蝙蝠对许多通过声音进行交流的昆虫以及青蛙构成了捕食压力。作为一种适应能力，许多昆虫物种进化出了对蝙蝠发出的回声定位信号的听觉敏感性，以防止被蝙蝠捕食。最近，发现欧洲麦氏耳蝠（Myotis myotis）和巴氏耳蝠（M. blythii oxygnathus）偷听螽斯科的螽斯（Tettigonia cantans）的求偶叫声。这些觅食蝙蝠在接近猎物和鸣叫的昆虫时会发出相当微弱的回声定位信号，而唱歌的昆虫可能很难检测到与捕食者相关的声音。本研究的目的是确定（1）欧洲螽斯产生的响亮的自身声音是否会影响对脉冲超声的检测，以及（2）如果螽斯的尾须上的风感器是否作为蝙蝠检测的备用感觉系统。我们通过结合行为方法来研究两种欧洲螽斯物种对脉冲超声的反应，以及通过记录风敏感中间神经元在欧洲麦氏耳蝠物种真实攻击期间的活动的电生理方法来研究蝙蝠检测问题。结果表明，鸣叫的 T. cantans 雄性对超声脉冲序列没有反应，而鸣叫的 T. viridissima 在超声脉冲落入静音间隔或与软半音节同时发生时，主要以短暂的歌声暂停做出反应。然而，这个结果强烈依赖于环境温度，在 21°C 时观察到的歌声中断概率比 28°C 时低。使用细胞外记录，发现螽斯的背侧巨神经元会对攻击的蝙蝠产生有规律的爆发。在风敏感中间神经元的第一次反应和接触之间，平均时间延迟为 860 毫秒。这个时间间隔对应于蝙蝠到猎物的距离约为 72 厘米。这个结果证明了螽斯的尾须系统在检测攻击蝙蝠方面的效率，并表明这种感觉系统对于被偷听蝙蝠攻击的鸣叫昆虫特别有价值。
