First published online May 2, 2008
Journal of Experimental Biology 211, 1612-1622 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013029
The effects of viscosity on the axial motor pattern and kinematics of the African lungfish (Protopterus annectens) during lateral undulatory swimming
Angela M. Horner* and
Bruce C. Jayne
Department of Biological Sciences, University of Cincinnati, PO Box
210006, Cincinnati, OH 45221-0006, USA
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Fig. 1. Ventral view of EMG locations (A) and lateral view of fish shape (B). A
ventral mirror view was used to reconstruct the lungfish outline and midline,
which was then partitioned into segmental lengths determined from radiographs.
The large vertical bar indicates the location of the border between the body
and the tail. The numbers indicate average anatomical locations for red muscle
EMG sites (see Table 1), with
bilateral sites denoted by asterisks. White muscle sites are indicated
parenthetically.
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Fig. 2. Grand means of speed (A), cycle duration (B) and distance traveled per
cycle (C) for each viscosity. Despite regular patterns of change in speed and
distance per cycle, only cycle duration was significantly affected by
viscosity (see Table 3). L,
length.
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Fig. 3. Series of lungfish midlines for one cycle from the same individual with
viscosities and swimming speeds of (A) 1 cSt, 0.20 L
s–1, (B) 10 cSt, 0.23 L s–1, (C)
100 cSt, 0.14 L s–1 and (D) 1000 cSt, 0.15
L s–1, respectively. Note that lateral displacement
and lateral bending increased most conspicuously anteriorly with increased
viscosity.
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Fig. 4. Effects of viscosity and longitudinal location on the mean values of
kinematics and muscle activity. (A) Lateral vertebral flexion
(βmax) is the maximum attained within a cycle. For a single
viscosity, flexion was always greatest in posterior sites, but with increased
viscosity the largest change in flexion occurred anteriorly. (B) EMG intensity
increased significantly with increased viscosity and was commonly greater in
more posterior locations. (C) EMG duty factor was nearly constant for all
longitudinal sites and viscosities.
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Fig. 5. EMGs from superficial red muscle from four ipsliateral longitudinal sites
from a single lungfish. EMG amplitude increased most conspicuously with
increased viscosity in anterior sites.
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Fig. 6. EMGs from superficial red muscle from three longitudinal sites with both
left side (L) and right side (R) showing unilateral and alternating motor
pattern. As a result of having EMG duty factors less than 50% of a cycle, each
longitudinal location briefly lacks muscle activity on either the left or
right side of the body.
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Fig. 7. Comparison of red (r) and white (w) muscle activity in 1 cSt (0.13
L s–1), 10 cSt (0.08 L
s–1), 100 cSt (0.13 L s–1) and 1000
cSt (0.16 L s–1) from a single longitudinal location
(site 7) in an individual lungfish.
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Fig. 8. Lateral vertebral flexion (β) and red muscle activity (horizontal
bars) from sites 1 (top) to 8 (bottom) versus time for two cycles of
an individual lungfish swimming in viscosities of 1, 10, 100 and 1000 cSt,
respectively. Bending convex to the left is represented by positive values of
β. The circles are raw data, and the lines represent a two-point running
average of the raw data. All EMG sites were on the left side of the fish.
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Fig. 9. Summary of bending and red muscle activity for mean values of four lungfish
in viscosities of 1 (A), 10 (B), 100 (C) and 1000 cSt (D). The time of all
graphs is standardized to 50% of a cycle when the body at 0.5 L was
bent maximally convex towards the side of muscle activity. The horizontal bars
indicate the average timing of muscle activity relative to bending at a
particular longitudinal location. Muscle activity between maximum convexity
and maximum concavity correlates with activity during contractile tissue
shortening.
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Fig. 10. (A) Lag time between EMG onset and when lateral flexion was maximally
convex on the side of muscle activity. (B) Lag time between EMG offset and
when lateral flexion was maximally concave on the side of muscle activity. (C)
Phase shifts between EMG onset and when lateral flexion was maximally convex
on the side of muscle activity. (D) Phase shifts between EMG offset and when
lateral flexion was maximally concave on the side of muscle activity. Values
of zero for both phase shifts indicate muscle activity during the entire time
of fiber shortening. Note that the magnitude of both phase shifts increased
significantly with increased viscosity.
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© The Company of Biologists Ltd 2008
