Red Squirrels Induce Stress Hormone To Have Bigger Pups

Stress is widely perceived as being bad, but for some squirrels stress is what will ensure their survival.

A study by Michigan State University and the University of Guelph in Canada shows how female squirrels use social cues to better prepare their offspring for life outside of the nest.

The results indicate that when stressed from the perceived threat of competition, red squirrel mothers booted stress hormone production during pregnancy which increased the size of their pups, and therefore upped pups' odds of surviving.

"Natural selection favors faster-growing offspring, and female red squirrels react accordingly to increase their pups' chances of survival," said researcher Ben Dantzer in a press statement. "Surprisingly, squirrels could produce these faster growing offspring even though they didn't have access to additional food resources."

It was a challenge for the team to prove that increased stress hormones increased survival when the availability of food is naturally thought of as the key factor of survival.

For part of the experiment, the researchers used recordings of territorial squirrels to create the illusion that the area contained a large population of squirrels. Females reacted to the commotion by producing more stress hormones while pregnant, and their pups grew faster. The researchers also manually manipulated the stress hormones in pregnant squirrels, and found the same results, which they say proves there is correlation between stress and faster growth of pups.

"Despite the widespread perception that being stressed is bad, our study shows that high stress hormone levels in mothers can actually help their offspring," Dantzer said.

Also of note, is that the reactions to stress were happening immediately and not generationally.

"When population density is high, only the fastest-growing offspring survive," said Andrew McAdam of Guelph University, who supervised Dantzer when they both were at MSU. "Our study also showed that rather than simply exhibiting lagged responses to environmental changes, the red squirrels may anticipate environmental changes using cues they pick up on during pregnancy