Remage-Healey Luke, Nowacek Douglas P, Bass Andrew H
Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14850, USA.
J Exp Biol. 2006 Nov;209(Pt 22):4444-51. doi: 10.1242/jeb.02525.
The passive listening hypothesis proposes that dolphins and whales detect acoustic signals emitted by prey, including sound-producing (soniferous) fishes. Previous work showed that bottlenose dolphins (Tursiops truncatus) behaviorally orient toward the sounds of prey, including the advertisement calls of male Gulf toadfish (Opsanus beta). In addition, soniferous fishes constitute over 80% of Tursiops diet, and toadfishes alone account for approximately 13% of the stomach contents of adult bottlenose dolphins. Here, we used both behavioral (vocalizations) and physiological (plasma cortisol levels) parameters to determine if male Gulf toadfish can, in turn, detect the acoustic signals of bottlenose dolphins. Using underwater playbacks to toadfish in their natural environment, we found that low-frequency dolphin sounds (;pops') within the toadfish's range of hearing dramatically reduce toadfish calling rates by 50%. High frequency dolphin sounds (whistles) and low-frequency snapping shrimp pops (ambient control sounds) each had no effect on toadfish calling rates. Predator sound playbacks also had consequences for circulating stress hormones, as cortisol levels were significantly elevated in male toadfish exposed to dolphin pops compared with snapping shrimp pops. These findings lend strong support to the hypothesis that individuals of a prey species modulate communication behavior in the presence of a predator, and also suggest that short-term glucocorticoid elevation is associated with anti-predator behavior.
被动听觉假说认为，海豚和鲸鱼能够探测猎物发出的声学信号，包括能发声的鱼类。此前的研究表明，宽吻海豚（瓶鼻海豚）会通过行为定位来捕捉猎物发出的声音，其中包括雄性海湾蟾鱼（海湾豹蟾鱼）的求偶叫声。此外，能发声的鱼类在宽吻海豚的食物构成中占比超过80%，仅蟾鱼就约占成年宽吻海豚胃内容物的13%。在此，我们使用行为学参数（发声）和生理学参数（血浆皮质醇水平）来确定雄性海湾蟾鱼是否能够反过来探测到宽吻海豚的声学信号。在蟾鱼的自然环境中对其进行水下声音回放实验，我们发现频率处于蟾鱼听觉范围内的低频海豚声音（“砰砰”声）能使蟾鱼的叫声频率大幅降低50%。高频海豚声音（哨声）和低频鼓虾的“砰砰”声（环境对照声音）对蟾鱼的叫声频率均无影响。播放捕食者声音也会对循环应激激素产生影响，因为与鼓虾的“砰砰”声相比，暴露于海豚“砰砰”声下的雄性蟾鱼体内的皮质醇水平显著升高。这些发现有力地支持了以下假说：猎物个体会在捕食者出现时调节其交流行为，同时也表明短期糖皮质激素升高与反捕食行为有关。
