Invertebrates have some wild adaptations that allow them to change size and shape, but for vertebrates, shrinking is a rare survival strategy.
Bears notably reduce their mass over winter, using up their fat stores during hibernation. Yet a few mammals actively shrink their skeletons, skulls and brains by 20 per cent or more as cold conditions advance.
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This occurrence is known as Dehnel’s phenomenon, after the Polish scientist August Dehnel, who first described the seasonal changes in shrews in 1949.
To date, this has been observed in shrews, European moles, stoats and weasels. All of these animals have a high metabolic rate and do not hibernate, meaning they need high-energy food sources to sustain them whatever the season.
Shrinking themselves also shrinks their food demands in winter, when resources are scarce.
Researchers from the Max Planck Institute of Animal Behavior in Germany have discovered more about this reversible process using MRI scans of common shrews. They found that the shrews’ brain cells lose water but crucially do not die, meaning that the animals retain their brain function.
It is hoped that further research in this area could inform medical treatments for humans suffering neurodegenerative diseases, including Alzheimer’s and Parkinson’s, that involve brain volume decline due to water loss.
“The next step is to learn how shrews regrow their brains so that we might find ways to teach human brains to do the same,” says one of the study’s authors (and expert in human brain disease at Aalborg University, Denmark), John Nieland.
Top image: common shrew. Credit: Christian Ziegler / Max Planck Institute of Animal Behaviour
