| Summary: | Published by and copyright of the University of Chicago Press. The definitive version of this article is available at: http://www.jstor.org/stable/10.1086/665407 Life-history theory predicts that selection will favor optimal levels of parental effort that balance benefits of current reproduction with costs to survival and future reproduction. The optimal level of effort depends on parental traits, offspring traits, and provisioning strategy. Additionally, how these factors influence effort may differ depending on the stage of reproduction. The relative importance of maternal and offspring traits on energy allocation to offspring was investigated in known-age Antarctic fur seals Arctocephalus gazella across four stages of reproduction, using birth mass and milk-consumption measurements. Maternal traits were important during three of the four stages investigated, with larger females giving birth to larger pups and investing more in pups during perinatal and molt stages. Pup mass influenced maternal effort during the premolt stage, and provisioning strategy influenced postnatal maternal effort at all stages. Energy provided to the offspring during an attendance visit was positively related to the duration of the foraging-trip/visit cycle; however, when investment was controlled for trip/visit cycle duration, the overall rate of energy transfer was similar across trip durations. In addition to strong effects of maternal mass, pup traits affected energy allocation, suggesting that pup demand is important in determining maternal care. These findings emphasize the importance of considering state variables in life-history studies and suggest that timing of measurements of effort in species with long provisioning periods may influence conclusions and our ability to make comparisons of reproductive effort among species. Research was funded by the U.S. AMLR Program and NSF Office of Polar Programs grant 0440687 to D.P.C, D.E.C., and M.E.G. B.I.M. was supported by the U.S. Environmental Protection Agency (EPA) under the Science to Achieve Results Graduate Fellowship Program and an NSF graduate fellowship. The EPA has not officially endorsed this publication, and the views expressed herein may not reflect the views of the EPA.
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