Stony Brook University’s Department of Ecology & Evolution, located in the Life Sciences Building. Researchers from the department have teamed up with European institutes and universities to study the Eurasian common shrew. ZOIE MASTRIANO/THE STATESMAN
The Eurasian common shrew has a biological superpower — this small rodent is able to shrink itself during winter and regrow during spring. Uncovering the peculiar way this shrew saves its energy during the winter may help advance research for treatments of neurodegenerative disorders in humans.
Researchers from Stony Brook University and other institutes and universities in Germany and Denmark published two studies that examined the Eurasian common shrew to understand the inner workings of Dehnel’s phenomenon, a rare adaptation where animals shrink their body mass, skulls and organs during winter and regrow them during spring.
Both studies were conducted in collaboration with researchers from John Jay College of Criminal Justice, the Max Planck Institute of Animal Behavior, Aalborg University and Universitat Autònoma de Barcelona.
William Thomas, the lead author on both papers and a former postdoctoral research associate in the Department of Ecology and Evolution explained that the Eurasian common shrew can reshape essential organs ranging from the liver to the brain.
“It’s hypothesized to be this energy-saving mechanism,” he said in an interview with The Statesman. “During winter, you’re spending less energy on maintaining this tissue and then you can regrow it during the time of spring when you have more energy.”
Wild Eurasian common shrews’ lifespans are approximately a year, which means they’re likely to experience Dehnel’s phenomenon only once.
If juvenile shrews are born in the spring and summer, then Dehnel’s phenomenon starts in autumn and completes in winter. As next spring arrives, they start growing back to normal size and finish growing in the summer. During spring, the shrews reach maturity and can breed.
Thomas clarified that the overall goal behind this project is to understand how the shrews change their brain mass in hopes of furthering research into treatments for certain disorders.
“Can we mimic what the shrews are doing to shrink and regrow their brains and help humans [who are undergoing neurodegenerative processes] do the same thing?” Thomas said.
The two studies touch on different aspects of the overall research into Dehnel’s phenomenon. The first, published in Genome Research, looks at the metabolic and molecular changes that occur during the shrew’s shrinkage and regrowth. The second, published in Molecular Biology and Evolution, looks into the genetic basis of the phenomenon, including a new sequenced genome for the Eurasian common shrew.
“One was done about 10 or 15 years ago that wasn’t as contiguous of a genome,” Thomas said. “We now have this kind of chromosomal reference for the shrew, which is not only important for our understanding of the seasonal size change, but can also be used as a resource for other scientists.”
He explained that although other organisms such as certain species of weasels, stoats and other types of shrews exhibit Dehnel’s phenomenon, the Eurasian common shrew, which is also the most abundant species of shrew, was studied due to how pronounced its seasonal changes are.
Liliana M. Dávalos, the principal investigator of both papers and a professor in the Department of Ecology and Evolution, quantified the change in size that occurs during Dehnel’s phenomenon.
“It is a very extreme change — if your head shrank by 25%, everyone around you would notice it right away,” she said.
Dehnel’s phenomenon shares many similarities with hibernation. They’re both methods of conserving energy so animals can survive the food scarcity winter brings. The major difference is that animals in hibernation remain in a dormant state, while animals that undergo Dehnel’s phenomenon stay active.
“What we hypothesize is that [Eurasian common shrews] don’t hibernate because they have such a high metabolic rate,” Thomas said. “If you’re only alive for a year and you’re going to sleep for a quarter of your life, it might not make too much sense.”
Researchers trapped wild shrews during these five stages of development: juveniles before shrinkage, during shrinkage, after shrinkage, then adults during regrowth and after regrowth.
Jeremy Searle, a professor at Cornell University’s Department of Ecology and Evolutionary Biology and whose lab focuses on the evolutionary biology of small mammals, explained why wild shrews were used for this project.
“Common shrews are not easy to breed in the laboratory, and that hinders some types of research,” he said. “However, with care, shrews can be maintained in captivity, and they can be studied in nature. For many of the sophisticated methods recently developed in biology, there is no need to have laboratory animals.”
Researchers collected blood samples from these shrews and removed and weighed their livers to confirm if Dehnel’s phenomenon was occurring. These samples were also used for further testing.
The analysis showed that during their shrinkage, the shrews showed regulatory changes in oxidative phosphorylation. That’s the last step in cellular respiration, a process where cells produce adenosine triphosphate, a high-energy molecule that powers our cells and our body as a whole.
It also increased the shrews’ fatty acid metabolism, which is a process where fatty acids are broken down to provide more adenosine triphosphate.
The researchers found that during autumn and early winter, the shrews show the highest rate of gluconeogenesis, a process where an organism produces glucose from inside its body. It’s what helps organisms survive starvation, which is prevalent during winter.
One of the more significant biological mechanisms researchers discovered behind the phenomenon is Forkhead box protein O1 or FOXO1 signaling. This signaling is the information the FOXO1 protein sends to activate certain cellular responses.
“This signaling is involved in metabolism, energy balance and it’s also involved in body size,” Dávalos said. “So in fall, as the [Eurasian common shrews shrink], they are increasing this signaling — it’s at a peak, but then in the spring, they have to grow back and this signaling drops.”
Along with its involvement in the shrew’s shrinking ability, the study cites other studies focusing on how FOXO1 signaling affects other organisms’ lifespans, including mice and humans.
“We have hypothesized from an evolutionary perspective that this is kind of an evolutionary tradeoff,” Thomas said. “The cost of shrinking and regulating your FOXO1 in a way might actually limit their lifespan, where they can only live for a year.”
Thomas correlates this strategy to terminal investment, which is the idea that as an organism’s chances of survival decrease, their reproductive efforts will increase.
“Shrink, survive the winter, so that way you can make it to next year, where you can mate and produce offspring,” he said. “But you won’t be able to actually make it to a second winter.”
Both humans and shrews have been studied in regard to FOXO1 signaling, which means replicating this phenomenon in other organisms may not be out of the question. This could be useful in ongoing research on neurodegenerative disorders, as the shrews regenerate tissue in their brain when they regrow their organs during spring.
“From understanding which proteins [and] genes are being expressed that are helping the shrew to shrink and regrow their brain, eventually we could come up with some sort of genes and proteins that could also help humans [to] regain neurofunction as their brains start to decrease in size during Huntington’s or Alzheimer’s disease,” Thomas said.