Wheatley Kathryn E, Bradshaw Corey J A, Harcourt Robert G, Hindell Mark A
Antarctic Wildlife Research Unit, School of Zoology, University of Tasmania, Private Bag 05, Hobart, TAS 7001, Australia.
Oecologia. 2008 Feb;155(1):11-20. doi: 10.1007/s00442-007-0888-7. Epub 2007 Nov 6.
Evolved patterns of resource expenditure for reproduction have resulted in a life history continuum across species. A strictly capital-breeding 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 capital-breeding animals, and was originally thought to provide a nutritional refuge for smaller females incapable of securing sufficient reserves during pre-partum 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 post-partum 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 54.9% of total energy loss to milk production. Later in lactation 30.5% 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 survival.
繁殖资源消耗模式的演变导致了物种间的生活史连续性。严格的资本繁殖策略在很大程度上依赖储存的能量进行繁殖，而收入繁殖则利用繁殖期获取的能量。然而，在一些典型的资本繁殖动物中已发现兼性收入繁殖现象，最初认为这为在产前觅食时无法获得足够储备的较小雌性提供了营养庇护。我们研究了威德尔海豹的乳汁成分和产奶量，以确定食物摄入对哺乳的辅助程度以及促成其表现的因素。乳汁成分与母体产后体重和状况无关，但在哺乳期会发生变化。变化很可能是对幼崽不同发育阶段的能量和营养需求的响应。在哺乳早期，雌性禁食，将总能量损失的54.9%用于产奶。在哺乳后期，用于产奶的能量增加了30.5%，有证据表明较大的雌性在哺乳期比小雌性进食更多。看来，威德尔海豹可能会采取灵活策略，利用猎物偶尔丰富的时期，根据当地资源水平调整繁殖投资，尽管这仅限于具有在哺乳期长时间潜水并利用不同资源的生理能力的较大雌性。这支持了以下假设：尽管体重和系统发育史解释了哺乳模式中大部分的变异（20 - 69%），但其余变异可能是对当地环境条件的生理适应所致。我们的研究证实，威德尔海豹采用混合资本 - 收入繁殖策略，且存在相当大的种内变异。关于收入策略带来的能量增益量以及对幼崽状况和生存的影响，仍存在疑问。
