Advances in thermal physiology of diving marine mammals: The dual role of peripheral perfusion

The ability to maintain a high core body temperature is a defining
characteristic of all mammals, yet their diverse habitats present
disparate thermal challenges that have led to specialized adaptations.
Marine mammals inhabit a highly conductive environment. Their
thermoregulatory capabilities far exceed our own despite having limited
avenues of heat transfer. Additionally, marine mammals must balance their
thermoregulatory demands with those associated with diving (i.e., oxygen
conservation), both of which rely on cardiovascular adjustments. This
review presents the progress and novel efforts in investigating marine
mammal thermoregulation, with a particular focus on the role of peripheral
perfusion. Early studies in marine mammal thermal physiology were
primarily performed in the laboratory and provided foundational knowledge
through in vivo experiments and ex vivo measurements. However, the
ecological relevance of these findings remains unknown because comparable
efforts on free-ranging animals have been limited. We demonstrate the
utility of biologgers for studying their thermal adaptations in the
context in which they evolved. Our preliminary results from freely diving
northern elephant seals (Mirounga angustirostris) reveal blubber’s dynamic
nature and the complex interaction between thermoregulation and the dive
response due to the dual role of peripheral perfusion. Further exploring
the potential use of biologgers for measuring physiological variables
relevant to thermal physiology in other marine mammal species will enhance
our understanding of the relative importance of morphology, physiology,
and behavior for thermoregulation and overall homeostasis.