The Effect of Litter Size and Litter Size Manipulations on Energetic Costs of Lactation in Grasshopper Mice.

繁殖在能量上是昂贵的，在哺乳动物中，这一成本完全由母亲通过怀孕和哺乳来承担。母亲的努力随着胎仔数量的增加而增加，但速度较慢，因此大胎仔中的单个后代获得的可用资源比例低于与母婴护理水平相关的后代，因此在胎仔大小和后代质量之间存在权衡。不幸的是，评估这种权衡并不容易，因为母亲生育后代的效率可能不同。这项研究将操纵北方蚱蜢鼠的胚胎和幼崽数量，以检查产仔数和哺乳能量成本之间的关系。能量数据将被用来检验个体对产仔数量的优化，并检验这样的假设，即每单位努力产下最大的后代。繁殖效率和成本将在母亲饲养自然大小的窝窝和人工增大和缩小的窝窝中确定。该项目的结果将为哺乳的能量成本以及产仔数和产仔数变异性的演变提供基础数据。

Reproduction is energetically costly and, in mammals, the cost is born entirely by mothers through gestation and lactation. Maternal efforts increases with litter size, but at slow rate such that individual offspring in large litters receive a smaller percentage of available resources than offspring are tied to the level of maternal care, so there is a tradeoff between litter size and offspring quality. Unfortunately, assessing this tradeoff is not simple because mothers may differ in their efficiency of producing offspring. This study will manipulate the number of embryos and pups in northern grasshopper mice to examine the relationship between litter size and the energetic cost of lactation. Energetic data will be used to test for individual optimization of litter size and to test the hypothesis that the modal litter size produces the largest offspring per unit effort. Reproductive efficiency and costs will be determined in litters where the mother is rearing natural-sized litters, and in artificially larger and smaller litters. The results of this project will provide foundation data on the energetic cost of lactation and the evolution of litter size and litter size variability