| Summary: | Dissertation (Ph.D.) University of Alaska Fairbanks, 2022 Predicting the impacts of environmental changes on animal populations requires a comprehensive understanding of the life history and physiological ecology of organisms in the wild, including the precise timing and regulation of annual biological events. In this dissertation, I assess how intrinsic factors including serum hormone concentrations and nutritional status relate to the critical annual events of reproduction, seasonal foraging, and pelage molt in an Antarctic marine predator, the Weddell seal (Leptonychotes weddellii). A large component of these assessments are comparisons between female Weddell seals that pupped in the current season (postpartum females) and females that have pupped in the past but did not give birth in the most recent pupping period (skip females). First, I examine how reproductive hormone profiles (serum progesterone, estrogen, prolactin, luteinizing hormone and follicle-stimulating hormone) vary between postpartum females and skip females across the austral summer. I found that skip females ovulated earlier than postpartum females and had higher serum estrogen and progesterone concentrations during early pregnancy. I also report a distinct midsummer decline in serum prolactin concentrations in both skip and postpartum seals. This decline may be due to seals becoming photorefractory at the time that the breeding period ends. Second, I characterize patterns in body mass changes and associated metabolic hormones and serum binding proteins (cortisol, growth hormone, insulin-like growth factor-1 (IGF-1), total and free thyroxine, total triiodothyronine, and IGF binding proteins 2 and 3) in Weddell seals across summer. I found that endocrine profiles of lactating seals reflected their depleted nutritional states, though their serum cortisol remained low. Postpartum females rapidly gained lean mass after weaning, which was likely supported by high serum growth hormone concentrations, while skip females lost body mass, probably ...
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