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2009
Meir, JU, Ponganis PJ.  2009.  High-affinity hemoglobin and blood oxygen saturation in diving emperor penguins. Journal of Experimental Biology. 212:3330-3338.   10.1242/jeb.033761   AbstractWebsite

The emperor penguin (Aptenodytes forsteri) thrives in the Antarctic underwater environment, diving to depths greater than 500m and for durations longer than 23 min. To examine mechanisms underlying the exceptional diving ability of this species and further describe blood oxygen (O(2)) transport and depletion while diving, we characterized the O(2)-hemoglobin (Hb) dissociation curve of the emperor penguin in whole blood. This allowed us to (1) investigate the biochemical adaptation of Hb in this species, and (2) address blood O(2) depletion during diving, by applying the dissociation curve to previously collected partial pressure of O(2) (P(O2)) profiles to estimate in vivo Hb saturation (S(O2)) changes during dives. This investigation revealed enhanced Hb-O(2) affinity (P(50)=28mmHg, pH7.5) in the emperor penguin, similar to high-altitude birds and other penguin species. This allows for increased O(2) at low blood P(O2) levels during diving and more complete depletion of the respiratory O(2) store. S(O2) profiles during diving demonstrated that arterial S(O2) levels are maintained near 100% throughout much of the dive, not decreasing significantly until the final ascent phase. End-of-dive venous S(O2) values were widely distributed and optimization of the venous blood O(2) store resulted from arterialization and near complete depletion of venous blood O(2) during longer dives. The estimated contribution of the blood O(2) store to diving metabolic rate was low and highly variable. This pattern is due, in part, to the influx of O(2) from the lungs into the blood during diving, and variable rates of tissue O(2) uptake.

Ponganis, PJ, Stockard TK, Meir JU, Williams CL, Ponganis KV, Howard R.  2009.  O-2 store management in diving emperor penguins. Journal of Experimental Biology. 212:217-224.   10.1242/jeb.026096   AbstractWebsite

In order to further define O-2 store utilization during dives and understand the physiological basis of the aerobic dive limit (ADL, dive duration associated with the onset of post-dive blood lactate accumulation), emperor penguins (Aptenodytes forsteri) were equipped with either a blood partial pressure of oxygen (P-O2) recorder or a blood sampler while they were diving at an isolated dive hole in the sea ice of McMurdo Sound, Antarctica. Arterial P-O2 profiles (57 dives) revealed that (a) pre-dive P-O2 was greater than that at rest, (b) P-O2 transiently increased during descent and (c) post-dive P-O2 reached that at rest in 1.92 +/- 1.89 min (N=53). Venous P-O2 profiles (130 dives) revealed that (a) pre-dive venous P-O2 was greater than that at rest prior to 61% of dives, (b) in 90% of dives venous P-O2 transiently increased with a mean maximum P-O2 of 53 +/- 18 mmHg and a mean increase in P-O2 of 11 +/- 12 mmHg, (c) in 78% of dives, this peak venous P-O2 occurred within the first 3 min, and (d) post-dive venous P-O2 reached that at rest within 2.23 +/- 2.64 min (N=84). Arterial and venous P-O2 values in blood samples collected 1-3 min into dives were greater than or near to the respective values at rest. Blood lactate concentration was less than 2 mmol l(-1) as far as 10.5 min into dives, well beyond the known ADL of 5.6 min. Mean arterial and venous P-N2 of samples collected at 20-37 m depth were 2.5 times those at the surface, both being 2.1 +/- 0.7 atmospheres absolute (ATA; N=3 each), and were not significantly different. These findings are consistent with the maintenance of gas exchange during dives (elevated arterial and venous P-O2 and P-N2 during dives), muscle ischemia during dives (elevated venous P-O2, lack of lactate washout into blood during dives), and arterio-venous shunting of blood both during the surface period (venous P-O2 greater than that at rest) and during dives (arterialized venous P-O2 values during descent, equivalent arterial and venous P-N2 values during dives). These three physiological processes contribute to the transfer of the large respiratory O-2 store to the blood during the dive, isolation of muscle metabolism from the circulation during the dive, a decreased rate of blood O-2 depletion during dives, and optimized loading of O-2 stores both before and after dives. The lack of blood O-2 depletion and blood lactate elevation during dives beyond the ADL suggests that active locomotory muscle is the site of tissue lactate accumulation that results in post-dive blood lactate elevation in dives beyond the ADL.

2008
Barber-Meyer, SM, Kooyman GL, Ponganis PJ.  2008.  Trends in western Ross Sea emperor penguin chick abundances and their relationships to climate. Antarctic Science. 20:3-11.   10.1017/s0954102007000673   AbstractWebsite

The emperor penguin (Aptenodytes forsteri) is extremely dependent on the extent and stability of sea ice, which may make the species particularly susceptible to environmental change. In order to appraise the stability of the emperor penguin populations at six colonies in the western Ross Sea, we used linear regression analysis to evaluate chick abundance trends (1983-2005) and Pearson's r correlation to assess their relation to two local and two large-scale climate variables. We detected only one significant abundance trend; the Cape Roget colony increased from 1983 to 1996 (n = 6). Higher coefficients of variation in chick abundances at smaller colonies (Cape Crozier, Beaufort Island, Franklin Island) suggest that such colonies occupy marginal habitat, and are more susceptible to environmental change. We determined chick abundance to be most often correlated with local Ross Sea climate variables (sea ice extent and sea surface temperature), but not in consistent patterns across the colonies. We propose that chick abundance is most impacted by fine scale sea ice extent and local weather events, which are best evaluated by on-site assessments. We did not find sufficient evidence to reject the hypothesis that the overall emperor penguin population in the Ross Sea was stable during this period.

Meir, JU, Stockard TK, Williams CL, Ponganis KV, Ponganis PJ.  2008.  Heart rate regulation and extreme bradycardia in diving emperor penguins. Journal of Experimental Biology. 211:1169-1179.   10.1242/jeb.013235   AbstractWebsite

To investigate the diving heart rate (f(H)) response of the emperor penguin (Aptenodytes forsteri), the consummate avian diver, birds diving at an isolated dive hole in McMurdo Sound, Antarctica were outfitted with digital electrocardiogram recorders, two-axis accelerometers and time depth recorders ( TDRs). In contrast to any other freely diving bird, a true bradycardia (fH significantly < f(H) at rest) occurred during diving [dive fH (total beats/duration)= 57 +/- 2 beats min(-1), f(H) at rest= 73 +/- 2 beats min(-1) ( mean +/- s. e. m.)]. For dives less than the aerobic dive limit ( ADL; duration beyond which [ blood lactate] increases above resting levels), dive f(H)= 85 +/- 3 beats min(-1), whereas f H in dives greater than the ADL was significantly lower (41 +/- 1 beats min(-1)). In dives greater than the ADL, f(H) reached extremely low values: f H during the last 5 mins of an 18 min dive was 6 beats min(-1). Dive f H and minimum instantaneous f(H) during dives declined significantly with increasing dive duration. Dive f(H) was independent of swim stroke frequency. This suggests that progressive bradycardia and peripheral vasoconstriction ( including isolation of muscle) are primary determinants of blood oxygen depletion in diving emperor penguins. Maximum instantaneous surface interval f(H) in this study is the highest ever recorded for emperor penguins ( 256 beats min(-1)), equivalent to f(H) at V-O2 max., presumably facilitating oxygen loading and post-dive metabolism. The classic Scholander-Irving dive response in these emperor penguins contrasts with the absence of true bradycardia in diving ducks, cormorants, and other penguin species.

2007
Kooyman, GL, Ainley DG, Ballard G, Ponganis PJ.  2007.  Effects of giant icebergs on two emperor penguin colonies in the Ross Sea, Antarctica. Antarctic Science. 19:31-38.   10.1017/s0954102007000065   AbstractWebsite

The arrival in January 2001 in the south-west Ross Sea of two giant icebergs, C16 and Bl5A, subsequently had dramatic affects on two emperor penguin colonies. B15A collided with the north-west tongue of the Ross Ice Shelf at Cape Crozier, Ross Island, in the following months and destroyed the penguins' nesting habitat. The colony totally failed in 2001, and years after, with the icebergs still in place, exhibited reduced production that ranged from 0 to 40% of the 1201 chicks produced in 2000. At Beaufort Island, 70 km NW of Crozier, chick production declined to 6% of the 2000 count by 2004. Collisions with the Ross Ice Shelf at Cape Crozier caused incubating adults to be crushed, trapped in ravines, or to abandon the colony and, since 2001, to occupy poorer habitat. The icebergs separated Beaufort Island from the Ross Sea Polynya, formerly an easy route to feeding and wintering areas. This episode has provided a glimpse of events which have probably occurred infrequently since the West Antarctic Ice Sheet began to retreat 12 000 years ago. The results allow assessment of recovery rates for one colony decimated by both adult and chick mortality, and the other colony by adult abandonment and chick mortality.

Ponganis, PJ, Stockard TK, Meir JU, Williams CL, Ponganis KV, Van Dam RP, Howard R.  2007.  Returning on empty: extreme blood O-2 depletion underlies dive capacity of emperor penguins. Journal of Experimental Biology. 210:4279-4285.   10.1242/jeb.011221   AbstractWebsite

Blood gas analyses from emperor penguins (Aptenodytes forsteri) at rest, and intravascular P-O2 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(O2)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-O2 profiles obtained from birds equipped with intravascular P-O2 electrodes and backpack recorders during dives revealed that (1) the decline of the final blood P-O2 of a dive in relation to dive duration was variable, (2) final venous P-O2 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-O2 values were indistinguishable in longer dives, and (4) final venous P-O2 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-O2 values and O-2 contents of penguins at rest.

2000
Ponganis, PJ, Van Dam RP, Marshall G, Knower T, Levenson DH.  2000.  Sub-ice foraging behavior of emperor penguins. Journal of Experimental Biology. 203:3275-3278. AbstractWebsite

Emperor penguins (Aptenodytes forsteri) were equipped with a remote underwater video camera, the Crittercam, to evaluate sub-ice foraging behavior while the birds dived from an isolated dive hole. Three birds dived and foraged successfully for Ih periods after being trained to wear and to dive with a harness for camera attachment. Video and depth profile recordings revealed that emperor penguins travel at shallow depths (<50 m), ascend to the undersurface of the ice to feed on fish, and descend back to depth to return to the exit hole. Although the mean durations of dives of individual birds with the Crittercam were 21-35 % shorter than the diving durations of these same birds without the camera, the dive profiles in both situations were similar, thus demonstrating a similar foraging strategy in birds diving without the camera. Despite shorter diving durations with the camera, the penguins were still successful at prey capture in 80 % of 91 dives greater than 1 min in duration. Prey included the sub-ice fish Pagothenia borchgrevinki. Hunting ascents (from depth to within 5 m of the surface) occurred in 85 % of dives, ranged from zero to three per dive, and were associated with successful prey capture in 77 % of 128 ascents, Occasionally, several fish were captured during a single ascent, These observations and this application of video technology create a model for further physiological and behavioral studies of foraging, and also emphasize the potential importance of shallow dives as sources of food intake for emperor penguins during foraging trips to sea.

Ponganis, PJ, Kooyman GL.  2000.  Diving physiology of birds: a history of studies on polar species. Comparative Biochemistry and Physiology a-Molecular and Integrative Physiology. 126:143-151.   10.1016/s1095-6433(00)00208-7   AbstractWebsite

Our knowledge of avian diving physiology has been based primarily on research with polar species. Since Scholander's 1940 monograph, research has expanded from examination of the 'diving reflex' to studies of free-diving birds, and has included laboratory investigations of oxygen stores, muscle adaptations, pressure effects, and cardiovascular/metabolic responses to swimming exercise. Behavioral and energetic studies at sea have shown that common diving durations of many avian species exceed the calculated aerobic diving limits (ADL). Current physiological research is focused on factors, such as heart rate and temperature, which potentially affect the diving metabolic rate and duration of aerobic diving. (C) 2000 Elsevier Science Inc. All rights reserved.

1999
Ponganis, PJ, Kooyman GL, Van Dam R, Lemaho Y.  1999.  Physiological responses of king penguins during simulated diving to 136 m depth. Journal of Experimental Biology. 202:2819-2822. AbstractWebsite

To evaluate blood N-2 uptake and the role of the respiratory volume (air sacs/lungs) as a N-2 and O-2 reservoir in deep-diving penguins, diving respiratory volume (V-DR), heart rate (f(H)), venous P-N2, blood volume (V-b) and hemoglobin (Hb) concentration were measured in king penguins (Aptenodytes patagonicus) during forced submersions and compressions equivalent to depths up to 136 m, V-DR was 69+/-18 ml kg(-1) (mean +/- S.D.) in 62 submersions ranging from 4.4 atmospheres absolute (ATA; 1 ATA=101 kPa) (34 m) to 14.6 ATA (136 m), Submersion f(H) averaged 30+/-7 beats min(-1) (N=18), approximately 20% of pre- and post-submersion values. Venous P-N2 values during and after submersions as deep as 11.2 ATA (102 m) were all less than 2.8 atmospheres N-2 (283 kPa) above ambient pressure, a previously measured threshold for symptomatic bubble formation. Mean V-b was 83+/-8 ml kg(-1) (N=6); [Hb] was 17.6+/-0.7 g dl(-1) (N=7), On a mass-specific basis, mean V-DR, and therefore total available N-2, is 41% of that in shallow-diving penguin species. Total body O-2 stores, calculated from measured V-DR, V-b, [Hb], muscle mass and myoglobin concentration, are 45 ml kg(-1), with 23 % in the respiratory system. This small respiratory fraction in comparison with that in shallow-diving penguins suggests a lesser reliance on the respiratory oxygen store for extended breath-holding and also a reduced uptake of nitrogen at depth.

1992
Kooyman, GL, Ponganis PJ, Castellini MA, Ponganis EP, Ponganis KV, Thorson PH, Eckert SA, Lemaho Y.  1992.  Heart rates and swim speeds of Emperor penguins diving under sea ice. Journal of Experimental Biology. 165:161-180. AbstractWebsite

Heart rate during overnight rest and while diving were recorded from five emperor penguins with a microprocessor-controlled submersible recorder. Heart rate, cardiac output and stroke volume were also measured in two resting emperor penguins using standard electrocardiography and thermodilution measurements. Swim velocities from eight birds were obtained with the submersible recorder. The resting average of the mean heart rates was 72 beats min-1. Diving heart rates were about 15% lower than resting rates. Cardiac outputs of 1.9-2.9 ml kg-1 s-1 and stroke volumes of 1.6-2.7 ml kg-1 were similar to values recorded from mammals of the same body mass. Swim velocities averaged 3 m s-1. The swim speeds and heart rates suggest that muscle O2 depletion must occur frequently: therefore, many dives require a significant energy contribution from anaerobic glycolysis.