Cervical air sac oxygen profiles in diving emperor penguins: parabronchial ventilation and the respiratory oxygen store

Blood oxygen transport and depletion in diving emperor penguins

Oxygen store management underlies dive performance and is dependent on the slow heart rate and peripheral vasoconstriction of the dive response to control tissue blood flow and oxygen uptake. Prior research has revealed two major patterns of muscle myoglobin saturation profiles during dives of emperor penguins. In Type A profiles, myoglobin desaturated rapidly, consistent with minimal muscle blood flow and low tissue oxygen uptake. Type B profiles, with fluctuating and slower declines in myoglobin saturation, were consistent with variable tissue blood flow patterns and tissue oxygen uptake during dives. We examined arterial and venous blood oxygen profiles to evaluate blood oxygen extraction and found two primary patterns of venous hemoglobin desaturation that complemented corresponding myoglobin saturation profiles. Type A venous profiles had a hemoglobin saturation that (a) increased/plateaued for most of a dive's duration, (b) only declined during the latter stages of ascent, and (c) often became arterialized [arterio-venous (a-v) shunting]. In Type B venous profiles, variable but progressive hemoglobin desaturation profiles were interrupted by inflections in the profile that were consistent with fluctuating tissue blood flow and oxygen uptake. End-of-dive saturation of arterial and Type A venous hemoglobin saturation profiles were not significantly different, but did differ from those of Type B venous profiles. These findings provide further support that the dive response of emperor penguins is a spectrum of cardiac and vascular components (including a-v shunting) that are dependent on the nature and demands of a given dive and even of a given segment of a dive.

A Physio-Logging Journey: Heart Rates of the Emperor Penguin and Blue Whale

Physio-logging has the potential to explore the processes that underlie the dive behavior and ecology of marine mammals and seabirds, as well as evaluate their adaptability to environmental change and other stressors. Regulation of heart rate lies at the core of the physiological processes that determine dive capacity and performance. The bio-logging of heart rate in unrestrained animals diving at sea was infeasible, even unimaginable in the mid-1970s. To provide a historical perspective, I review my 40-year experience in the development of heart rate physio-loggers and the evolution of a digital electrocardiogram (ECG) recorder that is still in use today. I highlight documentation of the ECG and the interpretation of heart rate profiles in the largest of avian and mammalian divers, the emperor penguin and blue whale.

Future trends in measuring physiology in free-living animals

Thus far, ecophysiology research has predominantly been conducted within controlled laboratory-based environments, owing to a mismatch between the recording technologies available for physiological monitoring in wild animals and the suite of behaviours and environments they need to withstand, without unduly affecting subjects. While it is possible to record some physiological variables for free-living animals using animal-attached logging devices, including inertial-measurement, heart-rate and temperature loggers, the field is still in its infancy. In this opinion piece, we review the most important future research directions for advancing the field of 'physiologging' in wild animals, including the technological development that we anticipate will be required, and the fiscal and ethical challenges that must be overcome. Non-invasive, multi-sensor miniature devices are ubiquitous in the world of human health and fitness monitoring, creating invaluable opportunities for animal and human physiologging to drive synergistic advances. We argue that by capitalizing on the research efforts and advancements made in the development of human wearables, it will be possible to design the non-invasive loggers needed by ecophysiologists to collect accurate physiological data from free-ranging animals ethically and with an absolute minimum of impact. In turn, findings have the capacity to foster transformative advances in human health monitoring. Thus, we invite biomedical engineers and researchers to collaborate with the animal-tagging community to drive forward the advancements necessary to realize the full potential of both fields. This article is part of the theme issue 'Measuring physiology in free-living animals (Part II)'.

Diving physiology of marine mammals and birds: the development of biologging techniques

In the 1940s, Scholander and Irving revealed fundamental physiological responses to forced diving of marine mammals and birds, setting the stage for the study of diving physiology. Since then, diving physiology research has moved from the laboratory to the field. Modern biologging, with the development of microprocessor technology, recorder memory capacity and battery life, has advanced and expanded investigations of the diving physiology of marine mammals and birds. This review describes a brief history of the start of field diving physiology investigations, including the invention of the time depth recorder, and then tracks the use of biologging studies in four key diving physiology topics: heart rate, blood flow, body temperature and oxygen store management. Investigations of diving heart rates in cetaceans and O2 store management in diving emperor penguins are highlighted to emphasize the value of diving physiology biologging research. The review concludes with current challenges, remaining diving physiology questions and what technologies are needed to advance the field. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.