Sea Mammal Research Unit, Scottish Oceans Institute, School of Biology, University of St Andrews, Fife KY16 8LB, UK
Hawaii Institute of Marine Biology, University of Hawaii at Manoa, P.O. Box 1346, Kaneohe, Hawaii 96744, USA.
J Exp Biol. 2020 Mar 12;223(Pt 5):jeb208470. doi: 10.1242/jeb.208470.
The acoustic startle reflex is an oligo-synaptic reflex arc elicited by rapid-onset sounds. Odontocetes evolved a range of specific auditory adaptations to aquatic hearing and echolocation, e.g. the ability to downregulate their auditory sensitivity when emitting clicks. However, it remains unclear whether these adaptations also led to changes of the startle reflex. We investigated reactions to startling sounds in two bottlenose dolphins () and one false killer whale (). Animals were exposed to 50 ms, 1/3 octave band noise pulses of varying levels at frequencies of 1, 10, 25 and 32 kHz while positioned in a hoop station. Startle responses were quantified by measuring rapid muscle contractions using a three-dimensional accelerometer attached to the dolphin. Startle magnitude increased exponentially with increasing received levels. Startle thresholds were frequency dependent and ranged from 131 dB at 32 kHz to 153 dB at 1 kHz (re. 1 µPa). Startle thresholds only exceeded masked auditory AEP thresholds of the animals by 47 dB but were ∼82 dB above published behavioural audiograms for these species. We also tested the effect of stimulus rise time on startle magnitude using a broadband noise pulse. Startle responses decreased with increasing rise times from 2 to 100 ms. Models suggested that rise times of 141-220 ms were necessary to completely mitigate startle responses. Our data showed that the startle reflex is conserved in odontocetes and follows similar principles as in terrestrial mammals. These principles should be considered when assessing and mitigating the effects of anthropogenic noise on marine mammals.
听觉惊跳反射是一种由快速突发声音引起的少突反射弧。齿鲸类动物进化出了一系列特定的听觉适应性，以适应水中听觉和回声定位，例如在发出咔嗒声时能够下调听觉敏感度。然而，目前尚不清楚这些适应性是否也导致了惊跳反射的变化。我们研究了两种宽吻海豚（）和一只伪虎鲸（）对惊跳声的反应。动物们被放置在一个圆环站内，暴露于不同频率（1、10、25 和 32 kHz）的持续 50 ms、1/3 倍频程带宽噪声脉冲，其强度逐渐增强。惊跳反应通过附着在海豚身上的三维加速度计测量快速肌肉收缩来量化。惊跳幅度随接收水平的增加呈指数增长。惊跳阈值随频率而变化，范围从 32 kHz 的 131 dB 到 1 kHz 的 153 dB（相对于 1 µPa）。惊跳阈值仅比动物的掩蔽听觉 AEP 阈值高出 47 dB，但比这些物种已发表的行为听力图高出约 82 dB。我们还使用宽带噪声脉冲测试了刺激上升时间对惊跳幅度的影响。惊跳反应随上升时间从 2 到 100 ms 的增加而减小。模型表明，上升时间需要在 141-220 ms 之间才能完全减轻惊跳反应。我们的数据表明，惊跳反射在齿鲸类动物中是保守的，遵循与陆生哺乳动物类似的原则。在评估和减轻人为噪声对海洋哺乳动物的影响时，应考虑这些原则。
