SNOWBIRD, UTAH — Wake up and smell the armpit.
That’s basically what Belding’s ground squirrels do in spring when hibernation has wiped out their memory of their society’s smells, says Jill Mateo of the University of Chicago. Using their own body odors as reference points, the ground squirrels figure out anew each year who’s kin and who’s not.
Self-sniffing as a guide to kinship has earned the nickname “armpit effect.” Biologists have theorized that plenty of animal species rely on their armpits when they do favors for kin or avoid relatives as mates. “There’s tantalizing evidence for the armpit effect in people,” Mateo says, but ruling out other possible explanations has been tricky in any species.
Armpit effects could certainly tip off any hibernation-fuddled ground squirrel to who’s a relative. But there’s an alternative explanation: that the animal learns the smell of mom and littermates in childhood, thus constructing a family-scent template for kinship.
“Kin recognition is the basis of a lot of our theory of the evolution of social behavior,” said behavioral ecologist Jan Randall of San FranciscoStateUniversity. She welcomes Mateo’s work as helping to reveal the mechanisms for such an important capacity.
Mateo took the fresh approach of switching baby ground squirrels into foster families at birth and then testing them after hibernation. Her results put Spermophilus beldingi ground squirrels among only a handful of examples for which experiments have ruled out childhood memory as an explanation for the ability to recognize kin by scent, Mateo said at the Animal Behavior Society meeting held in Snowbird, Utah, this week.
Knowing relatives by scent is a big deal for ground squirrels. They live high in the Sierra Nevada and Cascade ranges, with only some three months a year of above-ground time for eating and raising families. Females cooperate with their close relatives in such tasks as sounding alarms when danger looms.
When a ground squirrel digs its way up through the snow and emerges from hibernation, it has forgotten the smells of former neighbors that weren’t related. Mateo said. But the newly emerged ground squirrel does, somehow, respond to its kin.
Mateo switched around newborn ground squirrels so they would grow up in a family with a smell different from the armpit reference guides. In the wild, the ground squirrels usually hibernate alone, so at hibernation time she offered her test subjects individual tubs at a research center and burlap to shred into a nest. When the youngsters emerged from their tubs the next spring, Mateo studied their reactions to plastic cubes she had swiped across the cheeks of various other ground squirrels.
In a series of scent tests, the squirrels didn’t seem to remember their foster family smells, Mateo said. The ground squirrels reacted the same way (measured in sniffing time) when offered side-by-side cubes with scents of the foster family’s kin and scents of its non-kin.
Instead, the ground squirrels did distinguish between the scents of biological family kin and the scents of non-kin. Mateo concluded that any template developed in childhood had vanished and that the ground squirrels were relying on their armpits.
