| Summary: | Dissertation (Ph.D.) University of Alaska Fairbanks, 2015 Phocid seals rely on lipids in the form of a blubber layer as insulation and lipids as energy sources in blubber and muscle. The amount and lipid composition of blubber and other lipid stores vary throughout life within and among species of phocid seals. I hypothesized that this variation in regulation, allocation, and interactions among lipid stores is influenced by species, ontogeny, and tissue-specific thermal regimes in polar phocids: harp (Pagophilus groenlandicus), hooded (Cystophora cristata), and Weddell (Leptonychotes weddellii) seals. I investigated the thermoregulatory strategy of neonatal harp, hooded, and Weddell seals, and throughout the transition to an aquatic environment in harp seals. All three species had similar thermal resistance, though it was achieved differently using either lanugo or blubber. While there was variation in the main thermoregulatory strategy among species, no species possessed all thermal adaptations of adults. Harp and Weddell seals had higher surface area to volume ratios (SA:V), thus higher potential heat loss, though compensatory mechanisms for heat production were different between species. Harp seals were the only species with the potential for nonshivering thermogenesis (NST) in brown adipose tissue (BAT), whereas Weddell seals had the highest potential for shivering thermogenesis (ST) in their skeletal muscle. Hooded seals relied on blubber, and had a significantly lower SA:V than the other two species. As harp seal pups develop, their potential for NST declines and they shift to a reliance on blubber for insulation. By late weaning, harp seal pups have similar insulative capabilities as adults, and can likely meet the thermoregulatory challenges associated with living in water. In neonatal and young seals that have little blubber, other lipid stores such as BAT and skeletal muscle lipids provide heat-generating mechanisms (NST or ST) to offset potentially high rates of heat loss. The potential for NST ...
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