The Scent of Descent
Squirrels sniff to identify close and distant relatives
FRIDAY, March 29, 2002 (HealthDayNews) -- Do you have trouble getting along with your in-laws? Maybe you just don't like the way they smell.
Many animals, humans included, can use odor to detect who may be a close genetic relation. Depending on the species and their behavior patterns, an animal can use that ability to avoid inbreeding or to make decisions about risking its life in order to help close kin -- while leaving distant relatives and strangers to fend for themselves.
A new study by a Cornell University researcher who spent five years studying Belding's ground squirrels in the California mountains is the first to show how odor recognition allows precise determination of close genetic relatives.
"This is the first study to show which odors are used and how much those odors vary with kinship to see how animals use those odors to make their behavioral decisions about nepotism," says Jill M. Mateo, a psychology research associate at Cornell University.
The study appears in the April 7 issue of Proceedings: Biological Sciences journal.
Mateo found that when Belding's squirrels meet each other, it takes only seconds for them to resolve whether they're closely related. They do that by analyzing secretions from glands at the corners of their mouths. The squirrels also have scent glands on their backs.
Favoritism in Belding's squirrels is limited to mothers, sisters and daughters. A squirrel does recognize its nieces, grandmothers, and cousins but treats them more like outsiders.
The colonies of squirrel burrows are inhabited by females of various ages and some young males. Male squirrels leave their birthplace after they've been weaned.
Here's how Mateo cracked this scientific nut. She knew the family ties of the squirrels because she placed identity tags on each new litter over the years. To test the scent-detecting abilities of the squirrels, she rubbed plastic tubes along their scent glands to get an odor sample.
"I presented them to other squirrels and essentially asked the squirrels to tell me what they thought about those odors," Mateo says.
The squirrels quickly identified scents from their close relations but spent more time sniffing and evaluating odors from distant relatives or strangers. Mateo describes their sensitivity and ability to discriminate odors as astounding.
That's essential in survival situations, such as when a predator comes looking for lunch. A squirrel who sounds a chittering alarm to warn others that there's a coyote is more likely to be caught and eaten. So that sentinel squirrel has to know the risk is worthwhile, that it's acting in order to protect close kin.
While it may seem a stretch to connect this research to humans, it really isn't all that squirrelly.
"It's an opportunity to look at potential mechanisms that humans could be using," Mateo says.
The ability to recognize close kin is found in all mammals and other vertebrates such as birds. Studies like this allow scientists to get a better understanding of how that works and affects behavior, she says.
Previous research has shown that humans can use odor to detect genetic links to other people.
"The question is: Do we use this ability in our everyday lives and, more importantly, do we use it in our mate choice decisions?" Mateo says. For instance, does it kick into action to avoid marrying people who are too-closely related?
There's ongoing research into how odor affects dealings between strangers.
"We do find that, subconsciously, odors are influencing how we interact with people. It's not just that he or she has bad breath, so we find them aversive. It's more subtle than that. There's something about their odor that we like or dislike that influences the relationship itself," Mateo says.
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