European Moles Can Shrink Their Brain – A Rare Phenomenon
In the wintertime, European moles are facing an existential crisis. They require more food than is available during the colder months due to their high-limit mammal metabolisms. To deal with the seasonal difficulty, moles have found an unusual energy-saving strategy: shrinking their brains.
A new study led by Dina Dechmann of the Max Planck Institute of Animal Behavior discovered that European moles shrink their brains by 11% before winter and grow them again by 4% by summer. They are a new species of the animal noted for reversibly shrinking their brains via Dehnel’s phenomenon.
The study, however, goes beyond simply adding another species to the odd repertoire of brain-shrinking animals; it dives into the evolutionary conundrum of what drives them down this risky route. When the researchers analyse moles from different places, they determine that Dehnel’s phenomenon is caused by low temperatures rather than a shortage of food. Reduced brain tissue allows animals to consume less energy and so survive the cold.
Dehnel’s phenomenon was initially observed in shrew skulls, which were discovered to be smaller in the winter and larger in the summer. In 2018, Dechmann and colleagues published the first evidence that these unusual modifications in shrew skulls occurred throughout an individual’s life. Since then, Dechmann and colleagues have demonstrated that Dehnel’s phenomena occur in stoats and weasels. What these creatures have in common is an active lifestyle that keeps them on the verge of exhaustion.
It was evident to the scientists that reducing energetically expensive tissue, such as the brain, permits the animals to minimise their energy requirements. “We realised that Dehnel’s phenomenon helps these animals live in difficult circumstances.” But we still didn’t know what the true pressure points, the precise environmental triggers, were that were driving this process.”
The team has now responded to this by examining a new animal at the metabolic extreme. The researchers measured skulls in museum collections to see how two-mole species, the European mole and the Spanish mole, altered through time. They discovered that the European mole’s skull reduced by 11% in November and increased by 4% in spring, whereas the Spanish mole’s skull did not alter throughout the year.
Because the animals live in radically different climates, the researchers were able to determine that weather, rather than food availability, was the driver of brain alteration. “If it was merely a matter of food, we should observe European moles decreasing in winter when food was limited and Spanish moles shrinking in summer when food was scarce,” Dechmann said.
The study’s results go beyond resolving evolutionary issues, providing insights into how human bodies may heal after a major injury. “The fact that three distantly related groups of animals can decrease and then rebuild bone and brain tissue has enormous implications for study into disorders like Alzheimer’s and osteoporosis,” Dechmann adds.
“Winter conditions, not resource availability alone, may drive reversible seasonal skull size changes in moles” by Lucie Nováková, Javier Lázaro, Marion Muturi, Christian Dullin and Dina K. N. Dechmann, 7 September 2022, Royal Society Open Science.
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