Department of Biology, McMaster University, Hamilton, ON, Canada L8S 4K1
Division of Biological Sciences, University of Montana, Missoula, MT 59802, USA.
J Exp Biol. 2020 Dec 21;223(Pt 24):jeb215350. doi: 10.1242/jeb.215350.
High-altitude environments, characterized by low oxygen levels and low ambient temperatures, have been repeatedly colonized by small altricial mammals. These species inhabit mountainous regions year-round, enduring chronic cold and hypoxia. The adaptations that allow small mammals to thrive at altitude have been well studied in non-reproducing adults; however, our knowledge of adaptations specific to earlier life stages and reproductive females is extremely limited. In lowland natives, chronic hypoxia during gestation affects maternal physiology and placental function, ultimately limiting fetal growth. During post-natal development, hypoxia and cold further limit growth both directly by acting on neonatal physiology and indirectly via impacts on maternal milk production and care. Although lowland natives can survive brief sojourns to even extreme high altitude as adults, reproductive success in these environments is very low, and lowland young rarely survive to sexual maturity in chronic cold and hypoxia. Here, we review the limits to maternal and offspring physiology - both pre-natal and post-natal - that highland-adapted species have overcome, with a focus on recent studies on high-altitude populations of the North American deer mouse (). We conclude that a combination of maternal and developmental adaptations were likely to have been critical steps in the evolutionary history of high-altitude native mammals.
高海拔环境的特点是氧气含量低和环境温度低，已经多次被小型晚成性哺乳动物所占据。这些物种全年栖息在山区，长期忍受着寒冷和缺氧的环境。已经对允许小型哺乳动物在高海拔地区生存的适应机制进行了广泛研究，这些适应机制在非繁殖的成年个体中已经得到了很好的研究；然而，我们对特定于早期生命阶段和繁殖雌性的适应机制的了解极其有限。在低地原住民中，妊娠期间的慢性缺氧会影响母体的生理和胎盘功能，最终限制胎儿的生长。在出生后的发育过程中，缺氧和寒冷通过直接作用于新生儿的生理以及间接影响母体乳汁的产生和护理，进一步限制了生长。尽管低地原住民可以在成年后短暂地适应甚至极端的高海拔环境，但在这些环境中的繁殖成功率非常低，低地的幼崽很少能在慢性寒冷和缺氧中存活到性成熟。在这里，我们回顾了高原适应物种在母体和后代生理方面所克服的限制，包括产前和产后，重点是最近对北美的高山鹿鼠（）的高海拔种群的研究。我们的结论是，母体和发育适应的结合可能是高海拔原生哺乳动物进化历史中的关键步骤。
