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Fig. 6. Heart rate depends on temperature. (A) Scatter plots show the frequency of
the heartbeat in isolated hearts (N=10) in vitro as a
function of temperature. Each symbol represents a different heart. The number
of hearts failing at temperatures of 18, 20 and 22°C, was 2, 3 and 5,
respectively. (B) Heart rates from isolated hearts (filled squares) plotted
for comparison with heart rates recorded in intact lobsters in vivo
(filled circles) as a function of temperature. In both data sets there are
significant differences in mean heart rate across temperature
(P<0.0001). Assuming a linear trend, the estimated slopes (means
± s.e.m.) of the lines relating heart rate to temperature in intact
animals and in isolated hearts are 0.040±0.004 and 0.026±0.006,
respectively. *Data are significantly different at P<0.05;
**P<0.001; P-value based on contrast in repeated-measures
model. The P-values are not adjusted for the multiple comparisons.
Even with adjusted differences the data from 12 to 22°C are still
significant.) Only data from beating hearts were included for calculation of
the mean, therefore, for isolated hearts values of N are as follows:
from 2–16°C, N=10; at 18°C, N=8; at 20°C,
N=7; at 22°C, N=5. In intact animals only one heart
failed as temperature increased (at 20°C). Heart rates (means ±
s.e.m.) measured in intact animals in the wild [open symbols; data reproduced
from (Mercaldoallen and Thurberg,
1987)]. (C) Heart rates in intact animals (N=4) measured
over time as temperature increased from 2°C to a steady state level of
12°C. Horizontal bar indicates time period of temperature change (2 to
12°C) and time period of steady state temperature at 12°C.
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