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

Abstract

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.

Dollo meets Bergmann: morphological evolution in secondary aquatic mammals

“…Lineages classified as A2 have retained both terrestrial and aquatic thermic insulation adaptations, fur (water-repellent) and blubber layer, respectively—except for the sea otter ( Enhydra lutris ), which does not possess blubber but exhibits exceptionally dense fur—as they should be able to maintain thermal balance in both realms [ 21 ], thus possibly limiting their maximum body sizes. Nevertheless, large body sizes are related to the use of internal insulation as primary heat source, as large pinnipeds tend to rely more on blubber than fur insulation compared to smaller ones [ 96 ].…”

“…One of them, Bergmann's rule, describes a consistent pattern of increased body sizes in homeotherms associated with high latitudes or cold regions [25,26], a process likely be linked to lower relative heat loss in larger animals [27]. A similar pattern can be expected in aquatic lineages, as the large heat capacity of water increases the relative heat loss for aquatic animals compared to terrestrial ones [11,21].…”

“…When transitioning to water, many secondary marine clades, such as whales and turtles, evolved large body sizes (e.g. [11,[20][21][22][23][24]). However, the consistency of this pattern of body size increase linked to aquatic transitions across clades remains uncertain, partly because the numerous semi-aquatic freshwater lineages are often neglected.…”

The distribution of North Atlantic right whales in Canadian waters from 2015-2017 revealed by passive acoustic monitoring

“…This suggests that few NARWs travel as far north as the estimated distribution of their preferred prey, Calanus spp., which extends into arctic waters (Conover, 1988;Melle et al, 2014;Record et al, 2018). Documented forays by individuals into sub-zero Celsius waters of the GSL and higher latitudes indicates thermal tolerance should not be a constraint, which is corroborated by models suggesting healthy baleen whales are over-insulated (Kanwisher and Ridgway, 1983;Hokkanen, 1990;Favilla et al, 2021). However, NARWs have thinner blubber layers and poorer body conditions compared to the southern right whale species (Christiansen et al, 2022).…”

Comparison of infrared thermography of the blowhole mucosa with rectal temperatures in killer whales (Orcinus orca)

“…In marine mammals, several thermal adaptations are utilized, such as the specialized blubber layer instead of the subcutaneous fat employed by terrestrial mammals. A complex network of arteriovenous anastomoses perfuses the skin and blubber layers, and since they cannot respond to heat stress by evaporative cooling like terrestrial mammals, they are instead able to rapidly redistribute their core body heat via increased peripheral blood flow to extremities (dorsal fin, flukes, and flippers) using counter-current heat exchange systems (Scholander and Schevill, 1955;Rommel et al, 1992Rommel et al, , 1994Favilla et al, 2022).…”