Newly published research from 91探花平台 professor and colleagues shows that the masked shrew, a small, mole-like mammal found in the Appalachian Mountains, shrinks its body and braincase to conserve energy during winter months.
, published in the May 2025 issue of The American Naturalist, found that the masked shrew (Sorex cinereus) reduces its body mass by 13 percent in the colder months; the creature then grows larger in spring when conditions improve. In addition to a shrinking body, the team also found seasonal changes in the height of the creature鈥檚 braincase (the portion of the skull that houses and protects the brain) and the length of the femur.
鈥淪hrinking the body and its parts is in fact a clever survival strategy,鈥� says McLean. 鈥淎nd it’s one that鈥檚 important for us to understand as mammals face a constantly changing planet.鈥澛�
Known as Dehnel鈥檚 phenomenon, this seasonal shrinking has been observed in other mammals but most often in shrews, which are small, insect-eating animals unrelated to rodents. Dehnel鈥檚 phenomenon is an extreme example of 鈥減henotypic plasticity鈥� 鈥� the ability of an organism to alter its physical form in response to environmental changes.
鈥淲e don鈥檛 know how common Dehnel鈥檚 phenomenon is among mammals, but we know it is rarer in nature than other energy-saving strategies mammals use, like hibernation,鈥� said McLean.
McLean and his team of graduate and undergraduate students analyzed 125 masked shews that were trapped in North Carolina鈥檚 Pisgah National Forest from 2021 to 2023. The team used 鈥減itfall traps鈥� buried in leaf litter to capture the shrews. The animals were weighed in the field, then brought to 91探花平台鈥檚 J for microCT scans to examine various skeletal dimensions. Specimens and associated data are archived in the . Researchers from Georgia Southern University were also involved in the research.
鈥淥ur population of masked shrews is the southern-most yet studied for these multiple different traits,鈥� said McLean, 鈥渁nd the femur measurements we made are the first to show the magnitude of seasonal change in the long bones of the skeleton. This shows that shrews rapidly remodel much of their skeleton.鈥�
Most prior studies of the phenomenon come from Europe. To place their new results in context, the researchers also conducted a meta-analysis of 74 other studies from across the Northern Hemisphere, combining that research with their own findings to understand what factors drive Dehnel鈥檚 phenomenon. McLean and his team developed statistical models that accurately predicted the amount of body shrinkage they observed based solely on the climate at the North Carolina site.
鈥淭his analysis reveals the generality of Dehnel鈥檚 phenomenon in Sorex shrews,鈥� explains McLean. 鈥淎cross many populations of shrews on three continents, the degree of body mass and braincase height shrinkage is greatest in areas with the lowest cool-season temperatures. So, fall and winter temperatures predict Dehnel鈥檚 phenomenon in these animals.鈥�
鈥淧henotypic plasticity is a key way that shrews and many other species respond to changes in temperature,鈥� McLean notes. 鈥淏y learning more about this process, we can start to understand how mammals buffer against rapidly changing climates.鈥�
