Squid Studies Provide Valuable Insights Into Hearing Mechanisms
ScienceDaily (Oct. 15, 2010) — The ordinary squid, Loligo pealii -- best known until now as a kind of floating buffet for just about any fish in the sea -- may be on the verge of becoming a scientific superstar, providing clues about the origin and evolution of the sense of hearing.
The squid species Loligo pealii is the object of WHOI biologist Aran Mooney's research on the mechanism of hearing. (Credit: Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)
In a hangar-like research building at the Woods Hole Oceanographic Institution (WHOI), biologist T. Aran Mooney is exploring virtually uncharted waters: Can squid hear? Is their hearing sensitive enough to hear approaching predators? How do squid and other marine species rely on sound to interact, migrate, and communicate? Will the burgeoning cacophony of sound in the ocean disrupt marine life's behavior and threaten their survival?
"The sound in the ocean is increasing…commercial shipping, oil and gas exploration…those make a lot of noise," Mooney says. "And you don't know how that is going to affect the animal unless you know what it hears."
Mooney, a postdoctoral scholar at WHOI, has undertaken seminal investigations into the hearing of this seminal creature in the marine food web. His study is published Oct. 15, in theJournal of Experimental Biology.
"Almost every type of marine organism feeds somehow off the squid," says Mooney. Not just fish, but also many birds, seals, sea lions, and dolphins and toothed whales depend heavily on squid. Whales, according to Mooney, consume some 320 metric tons of squid a year; people eat another 280 metric tons annually.
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First published online October 15, 2010
Journal of Experimental Biology 213, 3748-3759 (2010)
Published by The Company of Biologists 2010
doi: 10.1242/jeb.048348
Sound detection by the longfin squid (Loligo pealeii) studied with auditory evoked potentials: sensitivity to low-frequency particle motion and not pressure
T. Aran Mooney1,2,*, Roger T. Hanlon1, Jakob Christensen-Dalsgaard3,Peter T. Madsen2,4, Darlene R. Ketten2,5 and Paul E. Nachtigall6
1 Marine Biological Laboratory, Woods Hole, MA 02543, USA
2 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
3 Institute of Biology, University of Southern Denmark, 5230 Odense M, Denmark
4 Zoophysiology, Department of Biological Sciences, Aarhus University, 8000 Aarhus C, Denmark
5 Harvard Medical School, Boston, MA 02114, USA
6 Hawaii Institute of Marine Biology, University of Hawaii, Kailua, HI 96744, USA
* Author for correspondence (amooney@whoi.edu)
Accepted 4 August 2010
Although hearing has been described for many underwater species, there is much debate regarding if and how cephalopods detect sound. Here we quantify the acoustic sensitivity of the longfin squid (Loligo pealeii) using near-field acoustic and shaker-generated acceleration stimuli. Sound field pressure and particle motion components were measured from 30 to 10,000 Hz and acceleration stimuli were measured from 20 to 1000 Hz. Responses were determined using auditory evoked potentials (AEPs) with electrodes placed near the statocysts. Evoked potentials were generated by bothstimuli and consisted of two wave types: (1) rapid stimulus-following waves, and (2) slower, high-amplitude waves, similar to some fish AEPs. Responses were obtained between 30 and 500 Hz with lowest thresholds between 100 and 200 Hz. At the best frequencies, AEP amplitudes were often >20 µV. Evoked potentials were extinguished at all frequencies if (1) water temperatures were less than 8°C, (2) statocysts were ablated, or (3) recording electrodes were placed in locations other than near the statocysts. Both the AEP response characteristics and the range of responses suggest that squid detect sound similarly to most fish, with the statocyst acting as an accelerometer through which squid detect the particle motion component of a sound field. The modality and frequency range indicate that squid probably detect acoustic particle motion stimuli from both predators and prey as well as low-frequency environmental sound signatures that may aid navigation.
Key words: cephalopod, statocyst, auditory, acceleration, hearing, invertebrate
Abbreviations: AEP, auditory evoked potential • c, sound speed • DAQ, data acquisition card • FFT, fast Fourier transform • p, pressure • peRMS, peak-equivalent root-mean square • p–p, peak-to-peak • SPL, sound pressure level • u, particle velocity • Vp–p, peak-to-peak voltage • , density
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