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First published online November 30, 2007
Journal of Experimental Biology 210, 4279-4285 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.011221

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Returning on empty: extreme blood O₂ depletion underlies dive capacity of emperor penguins

P. J. Ponganis^*, T. K. Stockard, J. U. Meir, C. L. Williams, K. V. Ponganis, R. P. van Dam and R. Howard

Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0204, USA

View larger version (19K): [in this window] [in a new window]   Fig. 1. Dive duration (A) and maximum depth (B) histograms of dives of emperor penguins equipped with backpack intravascular PO2 recorders (N=142).

View larger version (12K): [in this window] [in a new window]   Fig. 2. Air sac, arterial and venous PO2 profiles during shallow (less than 30 m), 3-min dives in three different birds. PO2 profiles from the air sac (EP 05) (Stockard et al., 2005) and aorta (EP 02) demonstrate initial compression hyperoxia and then a gradual decline in PO2 secondary to air sac O2 depletion and the decrease in ambient pressure during ascent. Vena caval PO2 slowly increased during the dive of EP 20. The PO2 data were recorded at 15 s intervals. Dives began at 0 time. Prior to the onset of the dive for the arterial profile, the bird had just surfaced for a breath after a prior dive.

View larger version (22K): [in this window] [in a new window]   Fig. 3. Venous PO2 and depth profiles from a 23.1 min dive. This shallow (<60 m maximum depth) dive is currently the longest reported dive of an emperor penguin. The blood O2 store was optimized in this bird (EP 19) with a pre-dive venous PO2 of 63 mmHg, which was equivalent to arterial values of birds at rest. PO2 gradually declined throughout the dive to a final value of 6 mmHg and then returned to pre-dive levels within 3 min. Grey background indicates dive time.

View larger version (20K): [in this window] [in a new window]   Fig. 4. Final PO2 and dive duration. Final PO2 values were recorded within the last 15 s of each dive. (A) Final venous PO2 and dive duration from nine emperor penguins (key shows individual symbols for each penguin). The variability in final PO2 values in relation to dive duration is presumably secondary to differences in metabolic rates during dives. In addition, the span of PO2 values at the aerobic dive limit (ADL) clearly indicates that the blood O2 store is not depleted at this limit, the dive duration associated with post-dive lactate accumulation. The exponential regression (y=96.416e–0.1216x, r2=0.94, P<0.001) was constructed from the highest final PO2 during each 1-min interval of dive duration. This represents the minimum rate at which final PO2 declines in relation to dive duration. (B) Comparison of final venous PO2, arterial PO2 and air sac PO2 (Stockard et al., 2005) demonstrates that air sac, arterial and venous PO2 values become indistinguishable in longer dives.