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First published online March 28, 2008
Journal of Experimental Biology 211, 1169-1179 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013235

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Heart rate regulation and extreme bradycardia in diving emperor penguins

Jessica U. Meir^*, Torre K. Stockard, Cassondra L. Williams, Katherine V. Ponganis and Paul J. Ponganis

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

View larger version (43K): [in this window] [in a new window]   Fig. 1. Examples of ECG records of emperor penguin 35 over 20 s intervals, (A) at the surface and (B,C) during diving. From this ECG record, heart rate (fH) was calculated as 214 beats min–1 (A) 12 beats min–1 (B) and 6 beats min–1 (C). Plus signs (red) represent detected peaks. The artifacts present in B and C correspond to wing strokes (as revealed by simultaneous review of stroke frequency and ECG profiles in this individual).

View larger version (31K): [in this window] [in a new window]   Fig. 2. Instantaneous heart rate (fH) and dive depth profiles from (A) a typical short (1.5 min) dive of emperor penguin 35, (B) a dive just longer than the ADL of emperor penguin 32, and (C) the longest dive in this study (18.2 min, emperor penguin 22). The fH data gap at the end of the dive in C resulted from a brief period of unusable ECG signal. fH in short dives does not approach extremely low values as in long dives. In C, fH is 6 beats min–1 for over 5 min, reaching a minimum of 3 beats min–1. Prominent features typical of dives are labeled as follows: a, surface interval tachycardia (pre- and post-dive); b, initial fH decline, immediately upon submersion; c, readjustment of fH (transient increase); d, secondary decline in fH; e, progressive bradycardia in long dives; f, increase in fH during ascent (prior to surfacing).

View larger version (16K): [in this window] [in a new window]   Fig. 3. (A) Minimum instantaneous heart rate (fH) during the dive vs dive duration. Individual birds (EP) are denoted by colors and symbols (see legend), N=9 birds, 125 dives. (B) Log transformation of minimum fH vs dive duration with regression equation for pooled dives: y=–107.27233x+1.81157, r2=0.738, P<0.0001.

View larger version (16K): [in this window] [in a new window]   Fig. 4. (A) Dive heart rate (fH) (total number of beats/dive duration) vs dive duration for emperor penguins diving at the isolated dive hole. Individual birds (EP) are denoted by colors and symbols (see legend), N=9 birds, 125 dives. (B) Log transformation of dive fH vs dive duration with regression equation for pooled dives: y=–58.5361x+2.00996, r2=0.755, P<0.0001.

View larger version (28K): [in this window] [in a new window]   Fig. 5. (A) Heart rate (fH) over a 10 min period in emperor penguin 22 resting on the sea ice. Note the regular, momentary tachycardias. (B) Heart rate (black) and impedance signal (red) from emperor penguin 32 during 1 min at rest. The maxima in the impedance signal were visually verified as corresponding to inspiration (grey squares). The tachycardia associated with each visually confirmed inspiration is associated with the upstroke in the impedance signal. Respiratory rate in this case is counted as 4 breaths min–1.

View larger version (34K): [in this window] [in a new window]   Fig. 6. Heart rate (fH), stroke frequency, and dive profiles of: (A) a relatively short (<2 min) dive of emperor penguin 31; (B) a 10 min dive of emperor penguin 35; (C) a 12 min, variable depth dive of emperor penguin 35. In B fH drops by a factor of 2 by the latter half of the dive, while stroke frequency remains constant. An increase in fH is also apparent prior to surfacing, again with no corresponding increase in stroke frequency. In C stroke frequency is always highest during descents (labeled a and b), but fH does not increase during descents. fH remained near 5 beats min–1 for much of the second half of the dive compared to around 35 beats min–1 in the first half. Stroke frequency, however, remains near 0.45 Hz, increasing only during descents and while near the surface.

View larger version (12K): [in this window] [in a new window]   Fig. 7. Log transformation of dive heart rate (fH) vs mean dive stroke frequency (A) and mean dive stroke frequency vs dive duration (B), N=5 birds, 47 dives. As seen in the linear fits in A the log of dive fH does not have a significant relationship to stroke frequency (y=0.508x+1.27, r2=0.082, P=0.051), and in B, dive stroke frequency has a significant, but weak negative relationship to dive duration (y=–17.70x+0.72, r2=0.267, P=0.0002).

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