Fig. 7. Thermal acclimation alters the temperature dependence of heart rate and ventilation. Heart and ventilation rates (mean ± s.d.) were measured simultaneously in single lobsters acclimated to cold (4°C; N=7) and warm (20°C; N=7) temperatures. (A) Heart rates are temperature dependent. For warm-acclimated lobsters the temperature-dependent increase in heart rate (slope=0.0635) is statistically significant (P=0.0001), whereas for cold-acclimated lobsters it is not (slope=0.04; P=0.06). The temperature-dependent decrease in heart rate at temperatures of 20°C and above is significant for both warm-acclimated and cold-acclimated lobsters (slope=–0.056, P<0.0001 and slope=–0.036, P<0.0001, respectively). (B) Ventilation rate increases as a function of temperature up to 20°C. For both warm- and cold-acclimated lobsters the increase in ventilation at temperatures 20°C is statistically significant (slope=0.1136; P<0.0001 for warm-acclimated lobsters; slope=0.0235, P=0.0001 for cold-acclimated lobsters). At temperatures >20°C ventilation decreases significantly in warm-acclimated lobsters (slope=–0.052, P=0.0001). In cold-acclimated lobsters, the temperature dependence of ventilation decreases at temperatures >20°C, although not to a significant extent (slope=–0.09, P=0.413). *Data from cold- and warm-acclimated lobsters are significantly different at P<0.05. Insets show samples of traces from ventilation and heart recordings in warm- and cold-acclimated lobsters at 2 and 20°C. Values of N are 5, except as follows: heart rate in cold-acclimated animals at 30°C (N=1), heart rate in warm-acclimated animals at 26°C (N=4) and 30°C (N=2), ventilation in cold-acclimated animals at 6°C (N=3), at 22°C (N=4), at 24°C (N=4), at 26°C (N=1) and at 28°C (N=1), and ventilation in warm-acclimated animals at 2°C (N=4), at 28°C (N=4) and at 30°C (N=2).