School of Life and Environmental Sciences, Wenzhou University, Wenzhou, Zhejiang 325035, China;
Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB39 2PN, Scotland, United Kingdom.
Proc Natl Acad Sci U S A. 2020 Sep 29;117(39):24352-24358. doi: 10.1073/pnas.2008974117. Epub 2020 Sep 14.
Predicted increases in global average temperature are physiologically trivial for most endotherms. However, heat waves will also increase in both frequency and severity, and these will be physiologically more important. Lactating small mammals are hypothesized to be limited by heat dissipation capacity, suggesting high temperatures may adversely impact lactation performance. We measured reproductive performance of mice and striped hamsters (), including milk energy output (MEO), at temperatures between 21 and 36 °C. In both species, there was a decline in MEO between 21 and 33 °C. In mice, milk production at 33 °C was only 18% of that at 21 °C. This led to reductions in pup growth by 20% but limited pup mortality (0.8%), because of a threefold increase in growth efficiency. In contrast, in hamsters, MEO at 33 °C was reduced to 78.1% of that at 21 °C, yet this led to significant pup mortality (possibly infanticide) and reduced pup growth by 12.7%. Hamster females were more able to sustain milk production as ambient temperature increased, but they and their pups were less capable of adjusting to the lower supply. In both species, exposure to 36 °C resulted in rapid catastrophic lactation failure and maternal mortality. Upper lethal temperature was lowered by 3 to 6 °C in late lactation, making it a critically sensitive window to high ambient temperatures. Our data suggest future heat wave events will impact breeding success of small rodents, but this is based on animals with a long history in captivity. More work should be performed on wild rodents to confirm these impacts.
全球平均气温的预计升高对大多数恒温动物来说在生理上微不足道。然而，热浪的频率和强度也将增加，这将在生理上更为重要。哺乳期的小型哺乳动物被认为受到散热能力的限制，这表明高温可能会对泌乳表现产生不利影响。我们测量了小鼠和条纹仓鼠的繁殖性能，包括牛奶能量输出（MEO），温度范围为 21 至 36°C。在这两个物种中，MEO 在 21 至 33°C 之间下降。在小鼠中，33°C 时的产奶量仅为 21°C 时的 18%。这导致幼崽生长减少 20%，但由于生长效率提高了三倍，幼崽死亡率有限（0.8%）。相比之下，在仓鼠中，33°C 时的 MEO 降低到 21°C 时的 78.1%，但这导致了显著的幼崽死亡（可能是杀婴）和幼崽生长减少 12.7%。仓鼠女性随着环境温度的升高，能够更有效地维持产奶量，但它们和它们的幼崽适应低供应的能力较差。在这两个物种中，暴露在 36°C 下会导致快速灾难性的泌乳衰竭和母体死亡。哺乳期后期，上致死温度降低了 3 至 6°C，这使其成为对高环境温度的敏感窗口。我们的数据表明，未来的热浪事件将影响小型啮齿动物的繁殖成功率，但这是基于在圈养环境中具有悠久历史的动物。应该对野生啮齿动物进行更多的研究，以确认这些影响。
