title: The high cost of reproduction in sea otters necessitates unique physiological adaptations.
abstract: Superimposed on inherently high basal metabolic demands, the additional energetic requirements of reproduction can push female sea otters beyond physiological limits. Indeed, the resulting energy imbalance contributes to disproportionately high rates of mortality at the end of lactation in this species. To examine and quantify metabolic changes associated with reproduction, we measured the resting metabolic rate (RMR) of a female sea otter across gestation, lactation and non-reproductive periods. Concurrently, measurements were made on a non-breeding control female. Our results suggest that RMR declines during gestation. Conversely, RMR increases during lactation, reaches a peak at 3-4 months postpartum, and remains elevated until weaning. Combining these direct measurements with published data, we found the cost of pup rearing to be significantly higher than previously estimated. High baseline energy demands and limited energy reserves, combined with significant lactation and pup rearing costs, appear to necessitate metabolic and thermal lability during key reproductive stages.
authors.affiliation: Department of Ecology and Evolutionary Biology, Long Marine Laboratory, University of California at Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95060, USA nthometz@ucsc.edu.
authors.forename: Nicole M
authors.identifier: 0000-0002-5035-5219
authors.initials: NM
authors.lastname: Thometz
authors.affiliation: Department of Ecology and Evolutionary Biology, Long Marine Laboratory, University of California at Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95060, USA.
authors.forename: Traci L
authors.initials: TL
authors.lastname: Kendall
authors.affiliation: Department of Ecology and Evolutionary Biology, Long Marine Laboratory, University of California at Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95060, USA.
authors.forename: Beau P
authors.initials: BP
authors.lastname: Richter
authors.affiliation: Department of Ecology and Evolutionary Biology, Long Marine Laboratory, University of California at Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95060, USA.
authors.forename: Terrie M
authors.initials: TM
authors.lastname: Williams
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D000831:Animals, Newborn; D001481:Basal Metabolism / Q000502:physiology; D005260:Female; D007774:Lactation / Q000502:physiology; D010041:Otters / Q000502:physiology*; D011247:Pregnancy; D012098:Reproduction / Q000502:physiology*; D012146:Rest / Q000502:physiology
keywords: Energetics; Enhydra lutris; Gestation; Lactation; Parental investment; Resting metabolic rate