Thompson S D, Nicoll M E
Nature. 1986;321(6071):690-3. doi: 10.1038/321690a0.
Traditionally, the fact that reproduction in eutherian (= placental) mammals tends towards prolonged intrauterine development and short lactation has been interpreted as an evolutionary advance over the metatherian (= marsupial) short gestation and prolonged lactation. However, it has recently been postulated that marsupial reproduction involves low initial energy investment and may be advantageous by minimizing energy loss if conditions necessitate early termination. Moreover, because marsupials have basal metabolic rates (BMRs) 30% lower than those of most eutherians, it has been suggested that daily and total energy expenditures during reproduction may also be lower. We have now tested the predictions that low BMR is maintained during reproduction and that initial investment is lower in marsupials. Using indirect calorimetry, we have made the first longitudinal measurements of energy expenditure during reproduction for a marsupial and for two eutherian species with low BMRs. We find that initial investment is lowest in a eutherian and total energetic expenditures were greatest for the marsupial. We also find that, relative to BMR, all three species have increased mean maternal resting metabolic rates (RMRs) during both gestation and lactation; this is the first evidence that mammals with low BMRs can substantially elevate metabolism for prolonged periods during gestation and lactation.
传统上，真兽亚纲（即有胎盘）哺乳动物的繁殖倾向于子宫内发育延长和哺乳期缩短，这一事实被解释为相对于后兽亚纲（即有袋类）的短妊娠期和延长哺乳期而言的一种进化进步。然而，最近有人提出，有袋类动物的繁殖初始能量投入较低，如果条件需要提前终止妊娠，通过将能量损失降至最低可能具有优势。此外，由于有袋类动物的基础代谢率（BMR）比大多数真兽类动物低30%，有人认为其繁殖期间的每日和总能量消耗也可能较低。我们现在对有袋类动物繁殖期间基础代谢率保持较低以及初始投入较低这两个预测进行了测试。通过间接测热法，我们首次对一种有袋类动物和两种基础代谢率较低的真兽类动物繁殖期间的能量消耗进行了纵向测量。我们发现，初始投入在一种真兽类动物中最低，而有袋类动物的总能量消耗最大。我们还发现，相对于基础代谢率而言，所有这三个物种在妊娠和哺乳期间母体的平均静息代谢率（RMR）都有所提高；这是首个证据表明基础代谢率较低的哺乳动物在妊娠和哺乳期间能够在较长时间内大幅提高新陈代谢。
