Naked Mole-Rat Queen’s Scent Keeps Colony Peaceful, Infertile

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A chemical signal emitted by the queen naked mole-rat suppresses reproduction and aggression among colony members, maintaining social order, according to a study published in Nature. Researchers identified isopropyl myristate (IPM), a compound present at higher levels in queens than in non-breeding individuals, as a key factor in regulating colony dynamics.

The study, led by Mohammed Khallaf, a postdoctoral researcher at the Max Delbrück Center for Molecular Medicine (MDC) in Berlin and Assistant Professor at Assiut University in Egypt, found that IPM reduces aggression and reproductive activity in naked mole-rats. These rodents, among the few mammals with eusocial behavior, live in colonies where only the queen reproduces, while others remain reproductively inactive.

“Queen scent goes in, prolactin stays up, progesterone and reproductive activation stay down,” Khallaf explained, describing how IPM influences hormonal pathways. Exposure to the compound increased prolactin levels—a hormone linked to fertility suppression—and decreased progesterone, a hormone associated with reproductive readiness.

Experiments with captive colonies provided strong evidence of IPM’s role. When researchers removed the queen, aggressive conflicts typically erupted as females vied to replace her. However, applying IPM to the colony’s bedding daily for 12 weeks prevented aggression, keeping the group stable. When the treatment stopped, conflicts resumed, resulting in one female’s death and another’s rise as the new queen.

The findings suggest that the queen’s authority extends beyond physical dominance, relying on chemical communication. Khallaf compared IPM to the pheromones used by queen bees and ants to regulate colony behavior, calling it “a mammalian version of a queen pheromone.” However, he cautioned that IPM is likely not the sole factor, as other cues—such as vocalizations and social interactions—may also play roles.

Naked mole-rats detect IPM through their sense of smell, a process critical to maintaining their highly structured society. The study highlights the complexity of mammalian social systems, challenging the notion that such behaviors are unique to insects.

Funded by institutions in Europe, Germany, and South Africa, the research underscores the potential for chemical signals to govern social hierarchies across species. While the experiments were conducted in captivity, the authors noted that further studies are needed to determine if the same mechanisms apply to wild populations.

The work adds to growing evidence that mammals, like social insects, use scent to coordinate group behavior. By linking chemical signals to hormonal changes and social stability, the study offers new insights into the evolution of eusociality—a trait long thought to be rare in mammals.

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How the Queen’s Scent Shapes Colony Dynamics

Unlike most mammals, where multiple females may reproduce, naked mole-rat colonies enforce strict reproductive hierarchies. Non-breeding females, despite being physiologically capable of reproduction, remain inactive due to social and environmental factors.

The study’s experiments revealed that IPM, a fatty acid ester, acts as a chemical messenger. When applied to colony bedding, it mimicked the queen’s presence, preventing the competitive aggression that typically follows her removal. This suggests that IPM serves as a “social glue,” reinforcing the queen’s dominance without physical coercion.

Khallaf’s team measured hormonal changes in exposed individuals, finding elevated prolactin levels and suppressed progesterone. Prolactin is known to inhibit ovulation in mammals, while progesterone stimulates reproductive readiness. The dual effect of IPM—boosting one hormone while lowering another—may explain its dual role in curbing reproduction and reducing conflict.

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Comparisons to Insect Pheromones and Mammalian Social Systems

The discovery of IPM’s role in naked mole-rat societies draws parallels to the pheromone-based regulation seen in ants, bees, and termites. In these insects, queen pheromones suppress reproduction in worker females, ensuring colony cohesion. The study’s authors argue that IPM functions similarly in naked mole-rats, bridging the gap between insect and mammalian social structures.

However, Khallaf emphasized that mammalian social systems are more complex. “While IPM is a key component, it’s unlikely to be the only factor,” he said. “Vocalizations, physical interactions, and environmental cues may also contribute to maintaining order.”

The research also raises questions about the evolutionary origins of eusociality. This convergence suggests that chemical communication may be a universal mechanism for governing group behavior, regardless of species.

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Implications for Understanding Social Behavior in Mammals

The findings challenge traditional views of mammalian social dynamics, which often emphasize competition over cooperation. By demonstrating how a chemical signal can regulate reproduction and aggression, the study provides a new framework for understanding eusociality in mammals.

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Next Steps and Unanswered Questions

Despite the study’s findings, many questions remain. For instance, how do naked mole-rats detect IPM at such low concentrations? What evolutionary pressures favored the development of this chemical communication system? And, crucially, does IPM function the same way in wild colonies as it does in captivity?

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“Queen scent goes in, prolactin stays up, progesterone and reproductive activation stay down,” said Mohammed Khallaf, lead author of the study.
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Mohammed Khallaf, Max Delbrück Center for Molecular Medicine and Assiut University.

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“The queen is not just the colony’s top animal; she also seems to broadcast a scent that helps hold the whole society together,” said Mohammed Khallaf.
Source
Mohammed Khallaf, Max Delbrück Center for Molecular Medicine and Assiut University.

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“IPM looks very much like a mammalian version of a queen pheromone,” said Mohammed Khallaf.
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Mohammed Khallaf, Max Delbrück Center for Molecular Medicine and Assiut University.