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First published online July 25, 2005
Journal of Experimental Biology 208, 2973-2980 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01687

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Air sac P_O2 and oxygen depletion during dives of emperor penguins

T. Knower Stockard¹, J. Heil², J. U. Meir¹, K. Sato³, K. V. Ponganis¹ and P. J. Ponganis^1,*

¹ Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0204, USA
² Anesthesiology Department, US Naval Medical Center, Balboa Hospital, San Diego, CA 92134, USA
³ International Coastal Research Center, The Ocean Research Institute, University of Tokyo, 2-106-1 Akahama, Ostuchi Iwate 028-1102, Japan

^* Author for correspondence (e-mail: pponganis{at}ucsd.edu)

Accepted 12 May 2005

In order to determine the rate and magnitude of respiratory O₂ depletion during dives of emperor penguins (Aptenodytes forsteri), air sac O₂ partial pressure (P_O2) was recorded in 73 dives of four birds at an isolated dive hole. These results were evaluated with respect to hypoxic tolerance, the aerobic dive limit (ADL; dive duration beyond which there is post-dive lactate accumulation) and previously measured field metabolic rates (FMRs). 55% of dives were greater in duration than the previously measured 5.6-min ADL. P_O2 and depth profiles revealed compression hyperoxia and gradual O₂ depletion during dives. 42% of final P_O2s during the dives (recorded during the last 15 s of ascent) were <20 mmHg (<2.7 kPa). Assuming that the measured air sac P_O2 is representative of the entire respiratory system, this implies remarkable hypoxic tolerance in emperors. In dives of durations greater than the ADL, the calculated end-of-dive air sac O₂ fraction was <4%. The respiratory O₂ store depletion rate of an entire dive, based on the change in O₂ fraction during a dive and previously measured diving respiratory volume, ranged from 1 to 5 ml O₂ kg^–1 min^–1 and decreased exponentially with diving duration. The mean value, 2.1±0.8 ml O₂ kg^–1 min^–1, was (1) 19–42% of previously measured respiratory O₂ depletion rates during forced submersions and simulated dives, (2) approximately one-third of the predicted total body resting metabolic rate and (3) approximately 10% of the measured FMR. These findings are consistent with a low total body metabolic rate during the dive.

Key words: air sac, Aptenodytes forsteri, dive, electrode, emperor penguin, hypoxia, metabolic rate, oxygen

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