Highland deer mice, alongside their lowland counterparts, participated in a simulated seven-week journey ascending to 6,000 meters. This study assessed the mice’s reactions to cold stress and decreasing oxygen levels to explore whether these deer mice possess a general adaptability or if certain groups have evolved specific traits suited to their local environments. The findings indicated that the high-altitude mice were more effective at regulating their body temperatures, showcasing adaptations that help them survive in low-oxygen circumstances.
Teams of mountaineering mice are enhancing our understanding of how evolutionary changes tailored to specific environments allow one species to flourish in varying habitats.
Led by Naim Bautista, a postdoctoral researcher in Jay Storz’s lab at the University of Nebraska-Lincoln, the research involved highland deer mice and their lowland relatives on a simulated ascent to 6,000 meters. Starting from sea level, the mice reached the peak of their “climb” after seven weeks. Throughout this period, Bautista monitored how the mice responded to cold stress and lower oxygen levels.
“Deer mice have the widest environmental range of any North American mammal, found from the plains of Nebraska to the highest Rocky Mountains and Sierra Nevada peaks,” stated Storz, Willa Cather Professor of biological sciences. “This study assessed their capability to thrive across varied altitudes, investigating if they developed specific adaptations to their local conditions or if they rely on a general ability to acclimatize.”
The specialized study was conducted at McMaster University in Canada, where the team divided the highland and lowland mice into two groups: a control group that remained at sea level and an acclimation group that underwent the seven-week ascent.
After spending seven days at sea level, the acclimated group was gradually exposed to conditions increasing in elevation by 1,000 meters each week, with oxygen levels adjusted to simulate the experiences of climbers. The researchers monitored how well each mouse could adapt to cold temperatures by measuring metabolic heat production.
Results indicated that the highland and lowland deer mice lack a shared general capacity to acclimatize to low oxygen conditions (hypoxia). As the simulated altitude exceeded 4,000 meters, it became clear that the highland mice had a significant advantage. They were more effective at regulating their body temperature in the face of dwindling oxygen levels, thanks to superior breathing efficiency and better oxygen transport through their circulatory systems.
“The data indicates that the highland and lowland mice do not possess a generalized ability to adjust to environmental changes,” Bautista remarked. “Instead, the highland mice have developed specific adaptations to cope with low oxygen levels that differ from those of the lowland prairie mice.”
Additionally, the study revealed that highland mice carry a genetic advantage that helps prevent thickening of the right ventricle of the heart, a common issue among lowland mammals dealing with low oxygen environments.
Bautista noted that these findings illustrate how adapting to specific conditions enables a widely distributed species like the deer mouse to flourish across different ecosystems.
“It underscores how population-specific evolutionary changes contribute to their adaptability,” Bautista explained. “Ultimately, these changes affect their chances of surviving in diverse habitats.”
Bautista is preparing to replicate the study, this time examining the responses of the yellow-rumped leaf-eared mouse, the highest-dwelling mammal in the world. This species lives in the Andes mountains at altitudes reaching up to 22,110 feet and was first discovered by Storz.
The deer mice study was recently published in PNAS. Other contributors to the research included Storz, Ellen Shadowitz and Graham Scott from McMaster University, Nathanael Herrera and Zachary Cheviron from the University of Montana, and Oliver Wearing from the University of British Columbia.