Mice use scent to determine who's the boss

Picture a mouse entering a narrow, transparent tube. Another mouse approaches from the opposite end. They meet in the middle, noses twitching, bodies tense. One mouse retreats, conceding the passage. The other presses forward, asserting dominance – a silent communication carried by scent.

Researchers at the Francis Crick Institute have been using this simple setup to uncover something remarkable: mice don’t just react to physical strength or size. They rely on scent to gauge social rank.

Mice use scent to identify social rank

Mice live in social hierarchies, much like humans. Some lead, some follow, some are forever in between. For a long time, scientists assumed these roles emerged from physical aggression or fixed behaviors. But a study published in Current Biology suggests otherwise.

Mice, it turns out, can read dominance through scent. They sniff out social status in the air and on the bodies of their peers. The researchers watched as mice encountered strangers and familiar cage mates.

They wanted to know whether a mouse could identify another’s rank without prior interaction. The answer was yes. The scent said it all.

Scent-based rank recognition in mice

In the tube test, two mice enter from opposite ends. The dominant mouse typically forces the other to back out. Researchers ranked mice within the same cage, creating a clear hierarchy.

Then they introduced unfamiliar mice, testing whether the scent cues still worked when the opponent was a stranger. The findings? Even without prior interactions, the mice accurately detected rank using only scent.

What happens in the dark?

Mice can’t rely on vision in complete darkness. So, the researchers plunged the testing room into blackness to eliminate visual cues.

The results stayed the same. Mice still recognized dominant opponents, proving that scent carried all the necessary information.

The team also castrated some mice to see if the removal of sex hormones affected scent signals. It didn’t. Dominance cues remained intact, suggesting that scent signals aren’t tied to hormones but to other chemical compounds.

Manipulating perception through scent

The researchers didn’t stop there. They tried manipulating rank perception through urine. By painting subordinate mice with urine from dominant males, they created temporary rank shifts.

Suddenly, the formerly submissive mice behaved like top dogs. Even strangers treated them as if they had climbed the social ladder. This powerful manipulation revealed that scent cues could override an individual’s actual social history.

“Our work offers an interesting perspective on social mobility: humans, like mice, can enter a new group of people but still maintain understanding of own social rank and gauge the social status of unfamiliar people,” noted Neven Borak, the study’s first author.

Mice use two scent systems

Mice use two chemosensory systems to read scent cues: the main olfactory epithelium (MOE) and the accessory olfactory bulb (AOB). To understand how these systems contribute to rank detection, the researchers disabled each one separately.

Mice with impaired olfactory systems still recognized rank. The same held true for those with damaged contact scent systems.

But when both systems were disrupted, the mice lost their ability to distinguish dominant from subordinate opponents. This dual reliance on scent systems underscores the importance of both airborne and contact-based scent cues in social interactions.

Scent cues help mice avoid conflict

Social life can get messy when animals clash over resources or mates. In mice, scent provides a way to avoid unnecessary fights. A quick sniff can tell a subordinate mouse to back down before a confrontation even begins.

By recognizing the scent of a dominant opponent, the mouse can retreat and avoid injury. This scent-based communication system not only maintains order but also reduces the risk of physical harm.

Universal scent signals

Do mice only recognize familiar scents? The researchers tested this by introducing mice from separate cages. Despite having no prior interactions, the mice still detected rank differences.

This ability to generalize rank recognition across groups suggests that scent cues carry universal signals of dominance. The implications are profound. Scent can act as a universal language, conveying social information without prior encounters.

Linking scent to social status

While scent clearly plays a role in rank recognition, how does the brain process this information? Previous studies have identified brain regions involved in self-rank detection, like the anterior cingulate cortex and the dorsomedial prefrontal cortex.

But how does the brain interpret opponent rank? The researchers suspect that sensory input from the MOE and AOB converges in areas like the medial amygdala and the bed nucleus of the stria terminalis.

These regions receive inputs from both olfactory and contact scent systems, suggesting a possible neural pathway for integrating social rank information.

Implications for social dynamics

Social hierarchies are not just a mouse problem. Humans also navigate complex social networks, constantly assessing their status relative to others. While humans rely more on visual and verbal cues, the underlying cognitive mechanisms for detecting rank may be similar across species.

“Humans, like mice, can enter a new group of people but still maintain understanding of own social rank and gauge the social status of unfamiliar people,” Borak notes.

The ability to perceive social status quickly can help avoid conflict, but it can also reinforce hierarchies, limiting social mobility and affecting health outcomes for those stuck at the bottom.

Future research directions

This study raises new questions. How do different brain regions work together to process scent cues and assess social rank?

What specific chemical compounds convey rank information? And how do physiological states, like stress or hunger, affect scent perception?

The researchers plan to use advanced imaging techniques and optogenetic manipulation to explore these questions, aiming to map the neural circuits that translate scent into social behavior.

Scent redefines hierarchies in mice

Mice don’t need words or physical strength to assert dominance. A scent can say it all. This study from the Crick Institute highlights how chemical cues can reshape social hierarchies, allowing mice to recognize and respond to dominance without direct confrontation.

For humans, the implications are equally intriguing. While we may rely less on scent, the underlying cognitive mechanisms for detecting social rank may still be at play, subtly influencing our interactions and shaping the way we navigate the social world.

The study is published in the journal Current Biology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–