Hypoxic events associated with hypothermia are cause of human brain dysfunctions, with no treatment. In contrast, diving seals exhibit an exceptional ability to tolerate brain hypothermia and hypoxia, while maintaining cognitive functions to forage and capture preys. Southern Elephant seals are the best divers among seals, that make them a unique neurological model to investigate physiological mechanisms to sustain repeated severe brain hypoxia and hypothermia. Free-ranging Southern Elephant seals will be equipped with new technology loggers to explore regional and brain hypothermia, hypoxia and neuronal activity at three developmental ages (pups, juveniles, adult) during prolonged dives. This will allow to compare different metabolic constraints and changes during diving experience. This comparative physiological approach will give a new way for better understanding organisms’ physiological adaptations to extreme hypoxic environments, that could provide a new way for future clinical applications.

By studying elephant seals, at different developmental ages (from newly born to adults), we will investigate how physiological responses, at both the cerebral and whole organism levels, can adapt organisms to hypoxic environments. To reach this aim, we will address the following specific questions.

1. At the organism level, we will investigate newly weaned pups, juveniles (i.e. unexperienced seals), and adult seals metabolism related to regional hypothermia (i.e. hypometabolism) while in prolonged apnea, to understand how such mechanisms can contribute to dives exceeding Aerobic Dive Limit (ADL).
    
2. At the brain level, we will map seals’ cerebral activation while diving as a function of (i) the development stage, from newborn to adults, (ii) the duration and depth of dives, and (iii) their consciousness and reactivity to external stimuli (control stimuli or natural stimuli such as preys).
    
3. 3) In parallel, we will determine potential deleterious effects of hypoxia/hypothermia on seals metabolic capacities to resist hypoxemia (lower blood oxygen) and to recover (i.e. muscle energetics, blood lactate) in relation with dive duration, to better understand foraging decisions and physiological tolerance to hypoxia.

Hypothermia in free diving activity was suggested to enhance ADL time in penguins and seals. Regional hypothermia in diving seals could be mediated by mechanisms similar to torpor, in particular due to the fact that entry into torpor is actively regulated, and by reducing the metabolic rate by 30-50% of basal euthermic level and core body temperature. To date, such mechanism has never been investigated in seals. However, while other animals remain inactive during torpor, hypothermic seals have to remain conscious enough to locate and catch their prey items. How seals maintain cognitive function during diving under hypothermia ensuring both metabolic reduction and possibly brain protection, remains unknown. 

By extension, the question is: how does the brain tolerate regular hypoxic insults and avoid deleterious effects of low oxygen while maintaining neuronal activity for efficient decision-making to forage successfully?