Laboratoire de Morphologie Fonctionnelle et Evolutive, Institut de Chimie-B6C, 4000 Liège, Belgium.
J Exp Biol. 2011 Nov 1;214(Pt 21):3613-8. doi: 10.1242/jeb.061218.
Piranhas are known to be sound-producing animals. Nevertheless, the biological significance of piranha calls remains unclear because sounds have been recorded only when specimens were held by hand or trapped in a gill net. These sounds are generated by rapid contractions of sonic muscles that insert on a broad tendon surrounding ventrally the cranial sac of the swimbladder. The piranha swimbladder is thought to play an important role in sound production as an impedance-matching device and as a resonator. However, the vibratory capacities of the cranial and caudal sacs and the exact role of both sacs in sound production remain poorly understood. In this study, three sounds were each associated to a specific behaviour. The first sound (type 1) was produced during frontal display; it had numerous pulses and lasted 140!±17 ms, with a fundamental frequency of 120±4 Hz. It corresponded to the sound made by hand-held fishes. The second sound (type 2) was produced during circling and fighting behaviour; it was a single pulse lasting 36±8 ms, with a fundamental frequency of 43±10 Hz. The third sound (type 3) corresponded to chasing behaviour and comprised three to four pulses, each lasting 3±1 ms, with a fundamental frequency of 1739±18 Hz. Using a laser vibrometer to study the swimbladder displacement when stimulated at different frequencies, it was demonstrated that the first two sounds corresponded to the swimbladder mechanism. By contrast, the third sound was associated with the jaw mechanism. The vibrometer indicated that the swimbladder is a highly damping structure, simply copying the sonic muscle contraction rate. This study provides two interesting insights. First, it shows the relationships between three kinds of piranha sound and three specific behaviours. Second, using muscle stimulation at different rates, it shows which simultaneous conditions are required for production of sound in this species. Swimbladder calls were produced by a muscle contraction rate of approximately 100 Hz because this periodicity allowed the swimbladder to vibrate. At this frequency range, the contraction-relaxation cycles of the swimbladder muscles engendered wall displacements that had short amplitudes and with only a small variability between them.
食人鱼是众所周知的发声动物。然而，食人鱼叫声的生物学意义仍不清楚，因为这些声音仅在标本被手持或被困在刺网中时才被记录下来。这些声音是由快速收缩的声肌产生的，这些声肌插入围绕鳔颅囊的宽阔腱上。人们认为，食人鱼的鳔在声音产生中起着重要作用，既是阻抗匹配装置，也是共鸣器。然而，颅囊和尾囊的振动能力以及两个囊在声音产生中的确切作用仍知之甚少。在这项研究中，三种声音分别与一种特定的行为相关联。第一种声音（类型 1）是在正面展示时产生的；它有许多脉冲，持续 140±17 毫秒，基频为 120±4 赫兹。它与手持鱼类发出的声音相对应。第二种声音（类型 2）是在盘旋和战斗行为时产生的；它是一个持续 36±8 毫秒的单脉冲，基频为 43±10 赫兹。第三种声音（类型 3）对应于追逐行为，由三到四个脉冲组成，每个脉冲持续 3±1 毫秒，基频为 1739±18 赫兹。使用激光测振仪研究在不同频率刺激下鳔的位移，结果表明前两种声音与鳔机制相对应。相比之下，第三种声音与下颌机制有关。测振仪表明，鳔是一种高度阻尼结构，简单地复制声肌收缩率。这项研究提供了两个有趣的见解。首先，它显示了三种食人鱼声音与三种特定行为之间的关系。其次，通过使用不同速率的肌肉刺激，它显示了该物种产生声音所需的同时条件。鳔叫声是通过大约 100 Hz 的肌肉收缩率产生的，因为这个周期性允许鳔振动。在这个频率范围内，鳔肌的收缩-松弛循环产生了振幅短且彼此之间变化很小的壁位移。
