In Brief

Squirrels have keen noses. So keen, in fact, they can recognize their relatives with a whiff, according to research published by psychologist Jill M. Mateo, PhD, in the British journal Proceedings: Biological Sciences (Vol. 269, No. 1492).

In her research on two species of ground squirrels, the Cornell University psychologist found that squirrels can recognize whether another squirrel is related to them--and to what degree--just by smelling the odors given off by their glands.

In a series of trials, Mateo gathered scent samples from "donor" Belding's ground squirrels and transferred the scents onto coded plastic cubes she placed at the entrances of burrows. Since researchers know that squirrels only need a quick sniff to recognize close kin, but take a longer time smelling the scent of distant kin or nonkin, Mateo measured how long a squirrel investigated the unfamiliar scent on the cube.

She found that the closer the investigating squirrel was related to the scent donor, the less time it spent sniffing the cube. For example, squirrels investigated the scent of their unfamiliar three-quarters siblings (squirrels who have the same father and whose mothers are sisters) for the shortest period of time, followed by more distant relations such as grandmothers and aunts. When scent donors were only remotely related, such as a cousin, the squirrels spent much more time smelling the cube, indicating that, even though the squirrels had never met, the investigating squirrel still could determine the donor squirrel's degree of kinship. They investigated unrelated squirrels' scents the longest.

Since female Belding's ground squirrels give preferential treatment to close female family members--mothers, sisters and daughters--but not more distant kin, such as nieces and nephews, the ability to decipher who's closely related is important, Mateo explains. For example, a female ground squirrel would probably endanger itself by crying to warn of a predator for its sister, but not for its cousins or unrelated kin. Saving the sister's life is similar to saving its own genotype, while saving an unrelated squirrel doesn't make evolutionary sense, she says.

Mateo also studied a second species of ground squirrel--one that doesn't give family preferential treatment. In these trials, she found that golden-mantled ground squirrels have the same kin "smelling" ability, even though they don't take advantage of it. That finding, Mateo says, counteracts the long-held assumption that animals don't exhibit nepotism because they can't tell the difference between kin and nonkin.

Mateo also points out that even humans have the ability to discriminate genetic differences in odors, referencing studies in which women prefer the smell of a stranger's T-shirt to the shirt of someone who has a similar genetic makeup. In species that can discriminate kin scent from nonkin scent, but treat both alike, the smelling ability could still be used to avoid incestuous relationships, Mateo theorizes.

"The study suggests there are these discrimination abilities out there that we've been ignoring for a long time," says Mateo. "Once you understand those mechanisms and abilities for the potential for kin recognition...we can better understand how they make or don't make use of that ability."