New tests of the amazing nose power of Belding’s ground squirrels have solved a 25-year-old puzzle about doing dangerous favors for relatives.
Classic studies beginning in 1977 showed that female Belding’s ground squirrels sound alarms or defend burrows to help their mothers, sisters, or daughters. Yet cousins and extended family get no more assistance than strangers do.
Are the ground squirrels unable to tell who their cousins are? Or do they just not go to the trouble of aiding them?
The answer seems to be the latter, says Jill Mateo of Cornell University. By sniffing, the squirrels can detect distant members of their extended family, yet they still treat them like outsiders, she reports in the April 7 Proceedings of the Royal Society of London B.
Earlier studies had only demonstrated kin recognition that leads to preferential treatment, Mateo says. Some biologists have assumed that what’s not observed isn’t there, she adds. “The study could make a lot of people rethink their data,” Mateo says.
The Belding’s ground squirrel lives in the western United States and Canada. A female ground squirrel is more likely to give a trilling alarm call of, say, a coyote on the horizon if an immediate relative lives nearby than if she has no close kin as neighbors. Females also assist mothers, sisters, and daughters–but not more-distant relatives or strangers–with the defense of their burrows against infanticidal intruders.
To see whether the ground squirrels could tell those other relatives from strangers, Mateo set up four mini-colonies of ground squirrels in enclosures.
She collected odors from the individual animals by rubbing small plastic cubes against glands on their face or back.
To see whether the odors alone reveal kinship, Mateo adapted a test method based on the extra attention that an animal pays to novel stimuli. First, she set out cubes rubbed on a ground squirrel unrelated to her test subjects. When the squirrels got used to that odor, she provided a series of cubes from relatives of that stranger.
The more distant the relative, the more time the squirrels spent sniffing the new cubes. Mateo concluded that the ground squirrels regarded the scents as increasingly novel as the relationship got more distant.
To see whether the squirrels made such distinctions with their own kin, Mateo presented them with pairs of cubes rubbed against relatives they had never met. Again, Mateo found sniffing time increasing the more distant the relative.
Overall, the squirrels sniffed longest at cubes perfumed by unrelated strangers. To Mateo, that indicates that the animals can smell a difference between cousins and strangers.
Mateo also tested the golden-mantled ground squirrel. This species is in the same genus as Belding’s ground squirrels and lives in similar places, but it leads a more solitary life. Yet it, too, can discriminate kin and strangers by odor.
Few researchers have examined whether asocial species have recognition skills, says George Gamboa of Oakland University in Rochester, Mich. His students have observed them in a solitary wasp. “We really know little about the evolution of kin recognition,” he says.
David W. Pfennig of the University of North Carolina at Chapel Hill says the study’s implication “is a very general one.” Researchers studying many kinds of animal behavior, such as reactions to predators, need to consider whether animals perceive distinctions even if they don’t act on them.
