First published online March 16, 2007
Journal of Experimental Biology 210, 1194-1203 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02730
Thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard shark and shortfin mako shark
Jeanine M. Donley1,
Robert E. Shadwick2,*,
Chugey A. Sepulveda3 and
Douglas A. Syme4
1 Biology Department, MiraCosta College, Oceanside, CA 92056, USA
2 Marine Biology Research Division, Scripps Institution of Oceanography
University of California, San Diego, La Jolla, CA 92093-0202, USA
3 Pfleger Institute of Environmental Research, Oceanside, CA 92054,
USA
4 Department of Biological Sciences, University of Calgary, Calgary,
Alberta, T2N 1N4, Canada
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Fig. 1. Isometric twitches recorded in anterior (solid lines) and posterior (broken
lines) red muscle from leopard and mako sharks at three temperatures (blue,
15°C; green, 20°C; red, 25/28°C), indicating the close similarity
in contraction and relaxation between the two body positions at each
temperature. Note also the greater effect of reduced temperature exhibited by
the mako samples.
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Fig. 2. Isometric twitch kinetics as a function of temperature and axial location
in leopard and mako shark red muscle. (A) Time to peak force development after
stimulus; (B) relaxation time to 50% of peak force. Pairwise comparisons of
times at each temperature indicate no significant differences between axial
location (P>0.05), except for the mako at 15°C where posterior
muscle (hatched bars) appeared to be slower than anterior muscle
(*P<0.05). Values shown are means ± s.d. (leopard shark,
N=3; mako shark, N=3–6). A, anterior location; P,
posterior location.
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Fig. 3. Sample work loops from anterior (ANT) and posterior (POST) red muscle of
the leopard shark operating under optimized conditions of stimulus duration
and phase of activation at 15°C. Strains used were based on those recorded
in vivo (±4% anterior, ±6% posterior). Arrows indicate
the trajectory of the work loops.
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Fig. 4. Sample work loops from anterior (ANT) and posterior (POST) red muscle of
the mako shark operating under optimized conditions of stimulus duration and
phase of activation at 15°C. Strains used were based on those recorded
in vivo (±5.5% anterior, ±9% posterior). Arrows
indicate the trajectory of the work loops.
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Fig. 5. Optimal stimulus duration (A,B) and activation phase (C,D) as a function of
cycle frequency and temperature in leopard (A,C) and mako (B,D) sharks. Data
for anterior and posterior locations (Tables
1,
2) have been pooled in this
graph. Values shown are means ± s.e.m. (N values are given in
the tables).
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Fig. 6. Maximal net work (A,B) and power (C,D) as a function of cycle frequency and
temperature in leopard (A,C) and mako (B,D) sharks. Values of net work are
normalized to the maximum value at each temperature. Values of power are
normalized to the maximum at 20°C for each species. Values shown are means
± s.e.m. (N values are given in the tables).
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Fig. 7. The cycle frequency at which maximal power is developed as a function of
temperature for RM from leopard and mako sharks.
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© The Company of Biologists Ltd 2007
