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First published online March 16, 2007
Journal of Experimental Biology 210, 1245-1254 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02709

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Temperature and acid–base balance in the American lobster Homarus americanus

Syed Aman Qadri¹, Joseph Camacho¹, Hongkun Wang², Josi R. Taylor³, Martin Grosell³ and Mary Kate Worden^1,*

¹ Department of Neuroscience, University of Virginia, Charlottesville, VA 22908, USA
² Division of Biostatistics and Epidemiology, University of Virginia, Charlottesville, VA 22908, USA
³ Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, FL 33149, USA

View larger version (8K): [in this window] [in a new window]   Fig. 1. Hemolymph pH varies as a function of acclimation temperature. Symbols represent mean (± s.e.m.) values for pH measured in lobsters acclimated to the indicated temperatures in artificial seawater in the laboratory (filled symbols) or to the ambient temperature of natural seawater in Woods Hole (MA, USA) in February (open symbols, WH) and in Salisbury Cove (ME, USA) in July (open symbols, SC). Numbers of samples measured under each condition are indicated. Inset: heart rates (mean ± s.e.m.) averaged over a period of 1 min in quiescent lobsters acclimated in the laboratory to water temperatures of 4 and 20°C.

View larger version (17K): [in this window] [in a new window]   Fig. 2. Hemolymph levels (mean ± s.e.m.) of total CO2, PCO2, CO 2–3 and HCO –3 vary with acclimation temperature. *Data are significantly different at P<0.05 (two-sample independent t-test). Conversion factor: 1 Pa=9.86x10–6 atm.

View larger version (8K): [in this window] [in a new window]   Fig. 3. The acid–base status of the hemolymph in a single lobster changes rapidly in response to a temperature increase. (A) Hemolymph pH (filled symbols) repeatedly sampled in a single lobster as the seawater temperature warmed from 2 to 12°C. (B) Hemolymph PCO2 (open symbols) measured in the same samples. In both plots the line indicates the kinetics of the temperature change from 2 to 12°C. Conversion factor: 1 Pa=9.86x10–6 atm.

View larger version (9K): [in this window] [in a new window]   Fig. 4. The time course of the change in acid–base status of a population (N=9) of lobsters abruptly exposed to a temperature change from 4 to 22°C. Symbols represent means ± s.e.m. *Data are significantly different from those at time 0 at P<0.05. Conversion factor: 1 Pa=9.86x10–6 atm.

View larger version (10K): [in this window] [in a new window]   Fig. 5. Davenport diagram illustrating changes in acid–base status (mean ± s.e.m.) over 24 h following an abrupt temperature change from 4 to 22°C. Iso-PCO2 (in µatm) lines are drawn. The buffer line at time 0 h demonstrates the hemolymph buffering capacity of H. americanus reported by Rose et al. (Rose et al., 1998) (–6.8 CO2 l–1 pH–1 unit). Conversion factor: 1 Torr=133.3 Pa.

View larger version (11K): [in this window] [in a new window]   Fig. 6. Changes in pH modulate lobster cardiac activity. The middle trace shows a continuous 10 min tension record of the spontaneous beating of the neurogenic lobster heart in vitro at 16°C. The pH of the saline perfusing the heart is indicated below the trace. Upper traces show three 8 s samples of tension recordings selected from the indicated portions of the 10 min recording to illustrate changes in the amplitude and frequency of the heartbeat. All traces are shown with the same vertical amplification. Scale bar, 2 min.

View larger version (17K): [in this window] [in a new window]   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).