Brown bears that are more prone to grating and rubbing against trees have more offspring and more mates, according to a University of Alberta study. The results suggest that there may be a fitness component to the poorly understood behavior.
“As far as we know, all bears do this dance, rubbing their backs against the trees, stomping their feet and leaving behind scents of who they are, what they are, what position they are in and maybe if they’re related, ”said Mark Boyce, an ecologist in the Department of Biological Sciences.
“What we’ve been able to show is that males and females have more offspring if they rub together, more surviving offspring if they rub together, and they have more mates if they rub together.”
The research team led by Boyce and postdoctoral researcher Andrea Morehouse identified and collected bear hair samples from 899 bear rubbing zones, which included trees, fence posts, and utility poles, in the Alberta Rocky Mountains south of Highway 3 for a period of four years. from 2011.
The team genotyped 213 brown bears (118 males, 95 females). Building on the work of Curtis Strobeck, who realized a decade earlier that emerging DNA methods could be used to identify individual bears, the team used data previously collected for more than 2,043 individual brown bears in the region. to create a family tree.
What the results showed was that bears that rub more frequently and on more sites do better.
For each rubbing object that a male bear was detected, the predicted number of mates increased 1.38 times. In addition, for each additional occasion that a male bear has been detected, the predicted number of offspring is multiplied by 1.37.
The researchers also observed the same relationships for female brown bears. Females with more mates were detected on more rubbing objects and on more occasions than females with fewer mates. For each additional rubbing object and occasion in which a female was detected, the predicted number of offspring increased by 1.42 and 1.55 times respectively.
“It appears that bears in good condition are more vigorous and they rub more, which could be correlated with breeding success,” he said.
This study also showed that this rubbing behavior helps females with calves avoid the territories of large males, often choosing marginal habitat near ranch buildings or closer to roads.
“It’s done by scent and the reason they do it is because big males are known to kill little ones,” Boyce said. “Big males won’t go anywhere near a building, but for females with cubs it’s an acceptable risk.”
He added that further studies could shed light on sexual selection in bears as well. While brown bears will fight tooth and nail to protect their territories, which will often include the territories of up to four females, females have a say.
In fact, previous research has shown that over 17 percent of all brown bear litters are sired by multiple males.
“The choice of women is a big issue,” Boyce said. “In this study, we proposed an alternative hypothesis that female brown bears use information obtained from the olfactory signals of males who rub each other throughout the season to choose paternity for their offspring.”
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Material provided by University of Alberta. Original written by Michael Brown. Note: Content can be changed for style and length.