Arctic Squirrels Are Bulking With Steroids For Winter

When you think the word "steroid," the first image that likely comes to mind is a muscle-bound meat head flexing in front of a mirror at the gym. But, while the consequential squeaky voice may be pretty on-point, you still will likely be surprised to learn that, in nature, it's squirrels who use "roids" to get buff.

That's at least according to a study recently published in the journal Biology Letters, which details how Arctic ground squirrels (Spermophilus parryii) spend their summers with testosterone and other "male" steroid hormones spiked to levels 10 to 200 times higher than your average ground squirrel.

A team of researchers from the University of Toronto in Scarborough and Mississauga say this sudden change in blood chemistry helps the squirrels survive a winter hibernation in their deep-frozen Arctic burrows.

Unlike ground squirrels in other parts of the world, the Arctic squirrels cannot burrow too deep, largely because permafrost makes the ground around them like concrete. Instead, these squirrels build more shallow burrows, which can get much colder than absolute zero (degrees Celsius).

Under those conditions, fat alone can't generate enough energy in the form of glucose to keep their brain and heart alive.

"And so what they do is they burn muscle," researcher Rudy Boonstra, of the University of Toronto, explained to CBC News.

These squirrels actually hibernate for eight months, and a series of field studies found that they traditionally have to gain at least 30 percent more muscle mass by late fall to make it through their long winter's nap.

They reach this new bulk with the help of naturally adapted adrenal glands on the top of their kidneys that pump out heavy concentrations of natural steroids into their blood each summer.

However, even knowing this, one question remained: "How do they get the benefits but not pay the costs? There are enormous costs to humans taking synthetic steroids," said Boonstra, citing "roid rage" and heart problems as just two known consequences.

To find out, Boonstra and colleagues Kaigo Mo and Douglas Monks looked to the cellular makeup of the squirrel to see if anything made it different than its warmer cousins.

The researchers found that Arctic ground squirrels had four times as many androgen receptors in their muscles as Columbian ground squirrels, allowing the body to adequately respond and benefit to the steroid spike without becoming overwhelmed.