It’s a smart survival mechanism, saving energy and withstanding extreme cold.
When winter comes, some animals leave for sunny places, while others sleep in a deep sleep during this harsh period. But the European mole – which often lives in the Netherlands and probably resides in your back garden – has a different trick. The researchers found that as winter approaches, the mole’s skull shrinks.
shrinkage
in New study Researchers took a closer look at the skulls of European moles preserved in the museum’s collections. They measured the size of the heads and noted the time of year the animal was collected. It leads to a surprising discovery. Because the size of the skull is not the same all year round. When winter comes, the skull of a one-year-old mole shrinks by as much as 11%. In the spring, the skull grows again by about four percent. A similar pattern was observed the following year, albeit to a lesser degree.
winter
Researchers suspect that this remarkable phenomenon is a reaction to cold and winter temperatures and not the result of a lack of food. Shrinkage is believed to provide animals with a great deal of energy, helping them deal with harsh winters.
Dehnil phenomenon
The European mole is not the only mammal able to periodically shrink and grow its skull. This phenomenon is also called the Dahnel phenomenon, after Professor Auguste Dahnel, who first observed this phenomenon in shrews in 1949. He saw that the size of the skulls of these animals varied seasonally. This phenomenon has since been observed worldwide in a number of small mammals, including stoats and weasels. However, it appears to be restricted to highly active animals that do not go into hibernation.
The skulls of a tigress can shrink by up to 20 percent in the winter. The skull of a shrew never regains its full size. Photo: MikeLane45. From Getty Images (via canva.com).
Although the reduction saves energy, it also involves a compromise. For example, previous research has shown that this affects the cognitive behavior of shrews. Exactly how this works, however, still needs further study.
shrew
Although the Dehnel phenomenon has been studied primarily in shrews, these cute creatures are not well suited as a living organism. They only live for an average of thirteen months, which means that they go through the Dehnel phenomenon only once. Unlike the shrew, the European mole lives for three years. Now that it has been shown that a mole is also able to shrink and grow its skull, it is likely that these animals will provide new insight into this somewhat unusual phenomenon. “Dahnel’s phenomenon provides a unique opportunity to study changes in brain volume,” said researcher Dina Deschmann. “And although shrews are the classic model, showing it in other animals, such as the European mole, has enormous implications. It might also be interesting to compare the Dehnel phenomenon in shrews and moles.”
live moles
Scientists plan to study the Dehnel phenomenon in live animals in follow-up research. This way they hope to find out exactly how it evolved. “I would like to study living moles to better understand how brain volume changes over time,” Dickman says. “We hope this also sheds more light on how mole behavior and energy expenditure are affected by this phenomenon.”
medical treatments
But research into the Dehnel phenomenon will not only expand our knowledge of the intelligent survival mechanisms of tunneling mammals. Extreme changes in skull size have also intrigued scientists in recent years, as they can provide insight into how the skeleton and other tissues develop that can change drastically — even after an animal is fully grown. There is hope that this will aid the search for new medical treatments for conditions that affect the growth and health of human bones and other organs.
“Some scientists are interested in the Dahnel phenomenon because more knowledge may lead to new treatments for neurodegenerative diseases and osteoporosis (a condition in which bones are less solid and strong due to lower bone density),” says Deichmann. By giving this phenomenon a broader taxonomic basis, there is a greater chance that further research will yield results. And that could be beneficial for us.”
