First published online August 18, 2005
Journal of Experimental Biology 208, 3421-3429 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01771
Mechanisms underlying the production of carapace vibrations and associated waterborne sounds in the American lobster, Homarus americanus
Heidi Pye Henninger and
Winsor H. Watson, III*
University of New Hampshire, Zoology Department, Durham, NH 03824,
USA
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Fig. 1. The percentage of lobsters that vibrated in (A) each size class and (B)
each month during body vibration surveys. Different letters denote
statistically significant differences in the percentage of lobsters that
vibrated in each group (P=0.05).
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Fig. 2. Body vibrations recorded from a 78 mm CL intermolt female. Individual
lobsters often produced signals of variable durations. (A) As an example, the
first vibration shown was 170 ms long while the second vibration was 1590 ms
in duration. (B) Expanded view of the first body vibration, denoted with a bar
in A. Scale: A, 20 mV, 250 ms; B, 20 mV, 25 ms.
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Fig. 3. (A) Mean frequency and (B) duration of body vibrations produced by three
size classes, each of five lobsters (<65 mm CL, 75–84 mm CL, >90
mm CL). Different letters denote statistically significant differences
(P=0.05).
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Fig. 4. Body vibrations give rise to waterborne acoustic signals. (A) Simultaneous
recording of a 300 ms body vibration, recorded in Chart software, and a
waterborne sound recorded using Canary software. (B) Expanded view of a
waterborne sound recorded in Canary software. Notice in the spectrogram that
the most intense sounds (darkest colors) are of a low frequency (<300
Hz).
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Fig. 5. Sounds and body vibrations are produced by contractions of the remotor and
promotor muscles. (A) Example of a simultaneous accelerometer recording of
body vibrations and remotor and promotor muscle electromyograms (EMGs). The
top photograph shows the anatomy of the two muscles (P, promotor; R, remotor).
(B) Expanded view of a section of a different simultaneous recording of
vibrations and muscle activity. There is a clear one-to-one relationship
between each wave in the accelerometer recording (V), or carapace movement,
and muscle activity. Scale: 10 mV for the top trace (vibration), 8 µV for
the EMG traces; time scale=200 ms; B, top, 8 mV, 20 ms; bottom, 4 µV, 10
ms.
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Fig. 6. Electromyogram (EMG) recordings of all four sonic muscles during the
production of a series of vibration pulses. (A) Lobsters most often produced
body vibrations by using the paired remotor and promotor muscles of only one
antenna (i.e. left or right) and often alternated between sides. Every lobster
tested used both sides in alternation, although in some individuals one side
was favored and used most often. (B) Lobsters also used simultaneous
contractions of the sonic muscles of both antennae to produce signals. In some
cases, both sets of muscles were used during the entire vibration, or, as seen
in B, one set was used for only part of the event. Vibrations produced by both
sets of muscles were not significantly longer in duration or different in
frequency than vibrations produced by one set. Scale: A and B, 20 mV for the
top trace (accelerometer), 16 µV for the EMG traces; time scale=200 ms.
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Fig. 7. Electromyogram (EMG) recordings of lesioned and intact muscles. In this
example, the left antennal muscles (both remotor and promotor) were lesioned
at their insertion into the musculature of the dorsal carapace, while the
right antennal muscles were kept intact. While the muscles of the left antenna
still contracted, they were unable to cause a vibration (recorded by the
accelerometer in the top trace). However, when the intact muscles of the left
antenna were active, they produced body vibrations. Lobsters continued to
alternate between the muscles of each side and did not avoid using the
lesioned muscles. Scale: 20 mV for the top trace (accelerometer), 16 µV for
the EMG traces; time scale=100 ms.
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Fig. 8. Accelerometer recordings demonstrating that electrical stimulation of sonic
muscles yielded carapace vibrations. Remotor muscle stimulation, and
stimulation of both the remotor and promotor muscles simultaneously, resulted
in body vibrations, while stimulation of promotor muscles did not cause body
vibrations. Electrical stimulations involving both muscles created vibrations
most similar in waveform and intensity to naturally produced sounds.
Horizontal bars indicate the periods of stimulation. Scale: 5 mV, 150 ms.
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Fig. 9. Spontaneous carapace vibrations produced by a male lobster. The vibrations
produced were lower in frequency and shorter in duration than those typically
elicited by startling or threatening lobsters. Scale: 20 mV for the top trace
(accelerometer), 8 µV for the middle EMG trace, 16 µV for the bottom EMG
trace; time scale=125 ms.
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© The Company of Biologists Ltd 2005
