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The startle reflex in echolocating odontocetes: basic physiology and practical implications.

ABSTRACT: 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 (Tursiops truncatus) and one false killer whale (Pseudorca crassidens). 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.

SUBMITTER: Gotz T

PROVIDER: S-EPMC7075047 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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The startle reflex in echolocating odontocetes: basic physiology and practical implications.

Götz Thomas T Pacini Aude F AF Nachtigall Paul E PE Janik Vincent M VM

The Journal of experimental biology 20200312 Pt 5

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 (<i>Tursiops truncatus</i>) and one false killer whale (<i ...[more]

PMID: 32165452

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Dataset Information

The startle reflex in echolocating odontocetes: basic physiology and practical implications.

Publications

The startle reflex in echolocating odontocetes: basic physiology and practical implications.

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