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Masked Shrews Exhibit Adaptive Shrinking Behavior in Winter
Recent research led by Dr. Bryan McLean of UNC Greensboro reveals that masked shrews, small mammal species native to the Appalachian Mountains, exhibit a fascinating survival mechanism: they contract their body and brain size to conserve energy during the colder months.
This study, detailed in The American Naturalist, reports that the masked shrew (Sorex cinereus) can shrink its body mass by approximately 13% during winter. Once temperatures rise in spring, the shrews return to their larger form. Alongside the reduction in overall mass, significant changes in the height of the braincase and femur length were also observed.
Dr. McLean notes, “The ability to shrink one’s body and parts is a remarkable strategy for survival. Understanding this response becomes increasingly critical as mammals adapt to a changing climate.”
Understanding Dehnel’s Phenomenon
This seasonal reduction in size, termed Dehnel’s phenomenon, has been noted in various mammals but is most prominently reported in shrews, which are insectivorous and have no close ties to typical rodents. This phenomenon exemplifies “phenotypic plasticity,” where an organism’s physical attributes can change in response to environmental pressures.
While the frequency of Dehnel’s phenomenon across different mammal species remains unclear, Dr. McLean argues it is less common than other energy-conserving adaptations, such as hibernation. His research team examined 125 masked shrews trapped in North Carolina’s Pisgah National Forest over a two-year period, from 2021 to 2023.
Research Methods and Findings
The researchers employed pitfall traps concealed in leaf litter to capture the shrews. After collecting the animals, they were weighed in the field and taken to the Joint School of Nanoscience and Nanotechnology at UNCG for microCT scans to assess various skeletal attributes. The specimens, alongside their data, have been preserved in the UNCG Mammal Collection. Collaborators from Georgia Southern University also contributed to the study.
Dr. McLean stated, “Our study represents the southernmost population of masked shrews examined for these traits, and the femur data we gathered is the first to demonstrate significant seasonal variations in the long bones, indicating rapid skeletal remodeling.”
Prior investigations focusing on this phenomenon primarily stem from European studies. To contextualize their new findings, the research team conducted a meta-analysis of 74 studies throughout the Northern Hemisphere, combining insights to discern the factors influencing Dehnel’s phenomenon.
Broader Implications of the Study
Dr. McLean and his collaborators created statistical models to predict the observed body shrinkage based on climate data from their North Carolina study site. “This analysis highlights the universality of Dehnel’s phenomenon in Sorex shrews,” he explained. “In environments experiencing lower cool-season temperatures, the extent of shrinkage in body mass and braincase height is most pronounced.”
“Phenotypic plasticity offers a critical response mechanism for shrews and many other species facing temperature fluctuations,” McLean remarked. “A deeper understanding of this adaptive strategy can illuminate how mammals cope with the rapid alterations attributed to climate change.”
More information:
Bryan S. McLean et al, Seasonal Body Size Plasticity and the Generality of Dehnel’s Phenomenon in Sorex Shrews, The American Naturalist (2025). DOI: 10.1086/735018
Source
phys.org