Mounting behavior, the thrusting motion dogs sometimes do against humans’ legs, is usually associated with sexual arousal in animals, but as it turns out, this is not always the case. New research conducted by neuroscientists explored the motivations behind mounting behavior in mice and discovered that sometimes there is a thin line between love and hate (or anger) in the mouse brain.
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Backstory
“Our lab is interested in understanding how social behaviors and underlying emotional states are controlled by the brain. While we were studying social behaviors in mice, we sometimes noticed that male mice would mount other males, in a way similar to how they would mount females.”
-Dr. Tomomi Karigo
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It was unclear whether these male mice tried to mate with a male because they simply mistook it for a female or if they knew it was a male but intended to establish dominance over it. The researchers hoped to understand whether a male mouse mounting another male mouse reflects a different intent than a mouse mounting a female mouse, and how mounting behavior is regulated in the brain.
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Study overview
The researchers first recorded videos of males mounting both male and female mice. Using machine learning, a type of software that learns and adapts through experience, they analyzed the videos to see whether there was anything different in the mounting behavior that was exhibited toward a male versus that toward a female mouse. The machine-learning analysis revealed no obvious difference in the mechanics of the mounting behavior.
The researchers then looked for other clues in the mounting males’ behavior that might differentiate female-focused versus male-focused mounting.
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Study findings overview
Male mice appeared to “sing” to females while mating with them. These songs, known as ultrasonic vocalizations, are too high-pitched for humans to hear, but can be picked up with a special microphone. The research team found that mounting mice sing only to female mice, not to males. In addition, when a male is mounting another male, the two animals usually end up fighting after a short period of mounting. This does not happen in the case of a female mounting partner.
These results suggested that mounting behavior toward a female has a different meaning than mounting behavior toward a male. Specifically, mounting toward a male is probably the expression of dominance or mild anger (aggressive mounting) and not a reproductive (or so-called affiliative) behavior.
Journal Reference: Karigo, Tomomi and Kennedy, Ann and Yang, Bin and Liu, Mengyu and Tai, Derek and Wahle, Iman A. and Anderson, David J. (2020) Distinct hypothalamic control of same- and opposite-sex mounting behaviour in mice. Nature . ISSN 0028-0836. (In Press) https://resolver.caltech.edu/CaltechAUTHORS:20200909-142458487 / Synopsis / Supplemental materials
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