Feast or famine evidence for mixed capital–income

Authors: Kathryn E Wheatley Corey J A Bradshaw Robert G Harcourt Mark A Hindell

Publish Date: 2007/11/06

Volume: 155, Issue: 1, Pages: 11-20

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Abstract

Evolved patterns of resource expenditure for reproduction have resulted in a life history continuum across species A strictly capitalbreeding strategy relies extensively on stored energy for reproduction whereas income breeding uses energy acquired throughout the reproductive period However facultative income breeding has been shown in some classically capitalbreeding animals and was originally thought to provide a nutritional refuge for smaller females incapable of securing sufficient reserves during prepartum foraging We examined milk composition and milk output for the Weddell seal to determine to what degree lactation was aided by food intake and what factors contributed to its manifestation Milk composition was independent of maternal postpartum mass and condition but did change over lactation Changes were most likely in response to energetic and nutritional demands of the pup at different stages of development During early lactation females fasted and devoted 549 of total energy loss to milk production Later in lactation 305 more energy was devoted to milk production and evidence suggested that larger females fed more during lactation than smaller females It appears that Weddell seals may exhibit a flexible strategy to adjust reproductive investment to local resource levels by taking advantage of periods when prey are occasionally abundant although it is restricted to larger females possessing the physiological capacity to dive for longer and exploit different resources during lactation This supports the assumption that although body mass and phylogenetic history explain most of the variation in lactation patterns 20–69 the remaining variation has likely resulted from physiological adaptations to local environmental conditions Our study confirms that Weddell seals use a mixed capital–income breeding strategy and that considerable intraspecific variation exists Questions remain as to the amount of energy gain derived from the income strategy and the consequences for pup condition and survivalWe thank P Brewin M Brock W Cook L Davis D Geddes A Hall P Isherwood C Littnan B Mooney P Nichols and volunteers from Scott Base for assistance in the field and laboratory This study was supported by funds from an Australian Research Council Discovery Project grant DP0342714 the University of Tasmania Institutional Research Grants Scheme and Sea World Research Rescue Foundation Inc We thank Antarctica New Zealand for providing logistical support and the Australian Antarctic Division for providing some field clothing ST Pochron and two anonymous reviewers provided constructive comments on the manuscript Data were collected under permits from the University of Tasmania Animal Ethics Committee A6790 and A6711 and the Department of Conservation of New Zealand Per/22/2002/149 and Per/17/2003/188 This study was conducted in accordance with the current laws of Australia and New Zealand

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