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Abstract

Despite having a shared common ancestor, marine mammals have undergone millennia of adaptations to become superior divers and endure a semi-aquatic lifestyle. Humans, by contrast, lack these specialized traits. While certain coastal populations have practiced free-diving for generations, competitive free-divers often achieve remarkable feats without such a lineage. Despite extensive research interrogating the diving physiology of mammals, the extent to which key traits are trainable versus inherited remains unresolved. The aim of this dissertation is to expand our understanding on what characteristics pertinent to diving capacity can be improved through rigorous training and which traits must be selected for. We addressed this through four studies. First, in recreational and elite human free-divers. we investigated the cardiovascular and hematological responses to dry dynamic apnea compared to exercise and static apnea trials. We further examined the potential influences of performance level and sex on these responses. Second, we analyzed hematological responses to apnea in elite human free-divers and northern elephant seals, species that regularly experience extreme and prolonged apneas. Third, we explored the metabolome across elite free-divers, non-diving humans, northern elephant, and grey seals. Finally, we assessed the influence of lifelong diving in the Ama divers of Japan compared to age and sex matched controls. We found that performance level had little influence on the magnitude of the cardiovascular and hematological responses to dynamic apnea, indicating that training has a mild effect on the physiological response to diving in humans. Further, we found the hematological response to static apnea in northern elephant seals as well as the metabolome in northern elephant seals and grey seals suggest enhanced physiological features to help mitigate the stress of diving including enhanced pH buffering, elevated antioxidant synthesis, and increased DNA repair. Lastly, we found that female Ama divers of Japan had comparable gas exchange efficiency as well as similar lung size and function as controls, suggesting that diving does not impact pulmonary function. Together, these data indicate that although human free-divers can withstand lifelong diving and achieve physiology defying feats, there are inherent traits in both northern elephant and grey seals that make them superior divers.