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The energy cost of reproduction in small rodents

Speakman John R.   

  • Online:2007-03-19 Published:2008-07-07


Speakman John R.   

  1. Aberdeen Centre for Energy Regul ation and Obesity, School of Biological Sciences, University of Aberdeen, Aberdeen, Scotland, UK, AB24 2TZ

Abstract: Reproduction is the mechanism by which animals perpetuate their genetic contribution to future generations. Reproduction therefore has clear advantages, but it also has costs. Principal among these are elevated energy demands. Studies of energy demands in small domesticated mice have revealed that food intake increases only slightly during pregnancy, but much more dramatically during lactation. Although the increase during pregnancy are small, this may reflect competition for space in the abdomen between the alimentary tract and the developing foetal mass and intake may be limited in this situation and impose constraints on the reproductive event. During lactation energy intake increase enormously, reaching an asymptote in late lactation. Studies in wild rodents generally show the same pattern of intake between pregnancy and lactation lending hope that our work in domestic mice may provide more generally applicable insights. Studies aiming to discover the nature of the limit on intake in late lactation have been performed for at least the past 15 years. The suggestion that the limits are imposed by capacities of the alimentary tract to digest food, or the of the mammary gland to secrete milk, do not adequately explain the available data. A novel hypothesis is that the limits may be imposed by the capacity of small rodents to dissipate heat. Heat loss capacity has long been known as a constraint on lactation in large mammals. Its significance in small rodents remains uncertain, but adjustments in the level of thermogenesis from brown adipose tissue that have been classically interpreted as releasing energy to support lactation may actually reflect a reduction in obligatory heat production to avoid hyperthermia. In spite of our advances in understanding in these areas we are still far from using this knowledge to understand even simple life history trade-offs.

Key words: Energy cost, Energy intake, Reproduction, Small rodent, Thermogenesis

摘要: 繁殖是动物向后代传递和保持遗传信息的方式。因此繁殖的意义是显而易见的,但也需要付出代价。主要代价是能量需求增加。在对小家鼠繁殖能量需求的研究中发现,能量摄入在妊娠期只是稍微增加,而在哺乳期则急剧增加。尽管在妊娠期增加的幅度很小,但这可能反映了消化道和发育的胎儿之间在动物腹中的空间竞争,从而可能使能量摄入受到限制进而影响到繁殖过程。哺乳期间,能量摄入急剧增加,在哺乳后期达到高峰并趋于稳定。对野生鼠的研究也表明,野生鼠妊娠期和哺乳期的能量摄入模式与小家鼠是基本相同的,这样我们在小家鼠研究工作中的发现就具有更普遍的适应意义。对哺乳后期能量摄入的限制机制研究至少已经进行了15 年。能量摄入受消化道消化能力的限制(中心限制假说)或者受乳腺泌乳能力限制(外周限制假说) 的假说,都不能合理地解释一些现有的结果。我们提出了一个新的假说,即能量摄入可能受啮齿动物散热能力的限制(热耗散限制假说)。很久以来,一直认为散热能力是对大型哺乳动物哺乳的一个限制因素,但它在小型啮齿动物中的意义尚不清楚。传统观点认为,啮齿动物哺乳期对褐色脂肪组织产热水平的调节是为了重新分配能量以满足哺乳所需;但现在看来,实际上可能是动物为了避免体温过高而降低其基本的产热水平。我们在这个领域已经有了一些进展,但要利用这些知识来理解即使很简单的生活史权衡等问题也还有很多的工作需要做。

关键词: 能量代价, 能量摄入, 繁殖, 啮齿动物, 产热