Nature
PUBLISHED
The animal world is pretty inventive when it comes to strategies to survive harsh winter weather; some species hunker down and sleep until spring, others have come up with ways to find food and shelter, and then there are those that simply embrace the freeze. Some animals, however, have taken it a step further by shrinking their organs to survive.
In a process known as Dehnel’s phenomenon, a small selection of small mammals can shrink their size by up to 20 percent or even more before the winter season. They are not simply losing weight either; they are actively decreasing the size of their bones, organs, and tissues.
What is even more remarkable is that in the spring, these features regrow – some only partially, some even larger than they were the previous summer. However, the element that is perhaps the most impressive is that the skull and brain mass undergo a massive change in size.
The phenomenon was first described in 1949 and has since been found in a number of shrews (all within the red-toothed shrew family), moles, and two species of small mustelids. While it is most well-studied in shrew species, shrews typically only live around 13 months, and so undergo this phenomenon only once in their lifetimes, which limits our understanding.
As a result, researchers are still trying to find out more about what factors lead to this unique adaptation. Is it a lack of resources that encourages the shrews to conserve energy in this way, particularly with energetically “expensive” tissues like the brain?
To investigate this further, a 2022 study looked at European moles (Talpa europaea), which have a similar ecology to shrews, do not hibernate, and have a very high energy expenditure through all that digging. The authors compared them with the Iberian mole (Talpa occidentalis) as they have different breeding cycles and live in different climates, which would allow them to assess whether this particular factor was having an effect.
The team found that in European moles, the skull height followed a seasonal pattern along their lifespan, being larger in summer and smaller in winter. “Individuals then shrank their relative skull size by 11%, reaching minimum size in November of the first year of their life,” explained the authors in their paper.
For this reason, they added European moles to the list of animals that exhibit Dehnel’s phenomenon – but not the Iberian mole. The latter did not change brain or skull size, leading the team to suspect that Dehnel’s phenomenon is linked to a winter climate and not only caused by a lack of resources.
Improving what we know about this phenomenon is not just something that improves our understanding of these animals either; it could go even further.
“That three distantly related groups of mammals can shrink and then regrow bone and brain tissue has huge implications for research into diseases such as Alzheimer’s and osteoporosis,” said study lead Dina Dechmann in a statement at the time. “The more mammals we discover with Dehnel’s, the more relevant the biological insights become to other mammals, and perhaps even to us.”
