From physiology to pixels: Resource allocation tradeoffs and noninvasive technologies for studying marine mammals
Long-term energy management shapes survival and reproductive success across mammals. Using the exceptional >60-year Weddell seal (Leptonychotes weddellii) demographic study in Erebus Bay, Antarctica, this dissertation links individual physiological traits to lifetime reproductive output in a long-lived free-living mammal. I investigated how markers of energy balance and metabolism, stress physiology, and iron mobilization relate to reproductive history to reveal mechanisms governing maternal trade-offs between self-maintenance and reproduction. High-quality females that had consistently higher reproductive output, exhibited elevated ‘stress hormone’ cortisol after weaning their pups compared to low-quality females, which likely prioritized recovery of lean mass. High-quality females also managed their energy reserves more efficiently during years of reproductive rest. In addition to supplying pups with energy across lactation, females transferred iron, a key component of hemoproteins that support large oxygen stores and aerobic performance in diving mammals. My findings demonstrated that adult females with greater iron reserves raised pups that also had larger iron stores by the time they are weaned, while iron isotopic signatures revealed mobilization and depletion of endogenous iron from tissues. Direct physiological measurements to understand resource allocation and energetics in wild animals are logistically difficult and costly to collect. Thus, I also developed and validated non-invasive techniques using infrared imaging coupled with Eulerian video magnification to accurately measure heart and respiration rates, proxies for metabolic rate, across species in a controlled zoological setting, then in pinnipeds in the field. Together, this work reveals the physiological mechanisms underlying carry-over effects and develops new tools for detecting energetic drivers of lifetime reproductive success in marine mammals.
Marine mammals, Animal physiology, Infrared imaging
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Massachusetts Institute of Technology and Woods Hole Oceanographic Institution