Journal of Experimental Biology
15 November 2006; Vol. 209, No. 22
Dolphin foraging sounds suppress calling and elevate stress hormone
levels
in a prey species, the Gulf toadfish
Luke Remage-Healey, Douglas P. Nowacek, and Andrew H. Bass
J Exp Biol 2006;209 4444-4451
http://jeb.biologists.org/cgi/content/abstract/209/22/4444?etoc
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%.
Highfrequency 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.
Key words: acoustic startle, predation, eavesdropping, natural
selection, stress, communication, corticosterone
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Dr Stuart Parsons
School of Biological Sciences
University of Auckland
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Auckland
New Zealand
Phone: +64 (0)9 373-7999 extn 85322
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