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

• Published in: Journal of Experimental Biology
• Main Authors: Ponganis, P. J., Stockard, T. K., Meir, J. U., Williams, C. L., Ponganis, K. V., van Dam, R. P., Howard, R.
• Format: Text
• Language: English
• Published: Company of Biologists 2007
• Subjects: Research Article; Aptenodytes forsteri; Emperor penguins
• Online Access: http://jeb.biologists.org/cgi/content/short/210/24/4279; https://doi.org/10.1242/jeb.011221

Blood gas analyses from emperor penguins ( Aptenodytes forsteri ) at rest, and intravascular P O 2 profiles from free-diving birds were obtained in order to examine hypoxemic tolerance and utilization of the blood O 2 store during dives. Analysis of blood samples from penguins at rest revealed arterial P O 2 s and O 2 contents of 68±7 mmHg (1 mmHg= 133.3 Pa) and 22.5±1.3 ml O 2 dl–1 ( N =3) and venous values of 41±10 mmHg and 17.4±2.9 ml O 2 dl–1 ( N =9). Corresponding arterial and venous Hb saturations for a hemoglobin (Hb) concentration of 18 g dl–1 were >91% and 70%, respectively. Analysis of P O 2 profiles obtained from birds equipped with intravascular P O 2 electrodes and backpack recorders during dives revealed that (1) the decline of the final blood P O 2 of a dive in relation to dive duration was variable, (2) final venous P O 2 values spanned a 40-mmHg range at the previously measured aerobic dive limit (ADL; dive duration associated with onset of post-dive blood lactate accumulation), (3) final arterial, venous and previously measured air sac P O 2 values were indistinguishable in longer dives, and (4) final venous P O 2 values of longer dives were as low as 1–6 mmHg during dives. Although blood O 2 is not depleted at the ADL, nearly complete depletion of the blood O 2 store occurs in longer dives. This extreme hypoxemic tolerance, which would be catastrophic in many birds and mammals, necessitates biochemical and molecular adaptations, including a shift in the O 2 –Hb dissociation curve of the emperor penguin in comparison to those of most birds. A relatively higher-affinity Hb is consistent with blood P O 2 values and O 2 contents of penguins at rest.