An international team of researchers, with the involvement of the UAB, has conducted a study that explains the evolutionary origins of the Dehnel phenomenon, a unique seasonal adaptation in small mammals that involves the ability to reduce and recover brain volume and function. The study is published in Molecular Biology and Evolution.
The Dehnel phenomenon is a case of extreme plasticity through which some mammals reduce and regenerate their brains according to the season. This mechanism allows species such as the common shrew to reduce the size of their brain, skull and other organs by up to 30% during the winter to save energy in conditions of extreme cold and food scarcity. In the spring, these tissues regenerate, making this phenomenon an exceptional example of physiological plasticity. Furthermore, comparative studies show that it is not exclusive to shrews: European moles and mustelids (such as weasels) also exhibit seasonal brain reductions, which extends the evolutionary framework of this strategy to mammals with high metabolisms.
Through comparative genomics and gene expression analysis in key tissues, such as the hypothalamus, the team identified genes associated with several fundamental processes, such as energy homeostasis and calcium signalling, essential for adjusting energy balance in demanding environments; the integrity of the blood-brain barrier, which ensures efficient control of molecules accessing the brain during the seasonal cycle; and water regulation, involved in reversible brain volume loss without cell death, a key finding for understanding how this adaptation is achieved.
"This work offers an integrated, evolutionary and molecular view of the Dehnel phenomenon. The identification of mechanisms related to energy regulation in the brain opens new questions about tissue plasticity in mammals and its potential biomedical application", highlights Aurora Ruiz-Herrera, lecturer at the Department of Cell Biology, Physiology and Immunology, researcher at the IBB-UAB and ICREA Acadèmia.
The plasticity reflected by the Dehnel phenomenon influences survival, reproduction, and resilience to climate variability. According to the research team, even though these species are not human, understanding the mechanisms that allow reversible reductions in brain volume without permanent damage could inspire new lines of research in neurology and metabolism. "The role of genes related to energy homeostasis and the blood-brain barrier points to possible biomarkers and therapeutic targets for neurodegenerative diseases, always with the necessary caution when extrapolating to humans", points out Aurora Ruiz-Herrera.
Reference article: Thomas WR et al. Genomic comparisons shed light on the adaptive basis of brain size plasticity and chromosomal instability in the Eurasian common shrew. Mol Biol Evol. 2026 Jan 9. doi: 10.1093/molbev/msag006.
