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Naked mole-rat (Heterocephalus glaber) queens produce a chemical that prevents other females in their colony from reproducing. A study published today in Nature suggests that this compound maintains a strict social structure that is dominated by one queen, even when the animal is not present. The chemical’s odour alters the production of hormones in other females, which stifles their ability to bear young. |
Max Delbrück Center Identifies Isopropyl Myristate as a Reproductive Suppressant
Naked mole-rat queens maintain their dominance and suppress reproduction in colony subordinates using a specific chemical signal. Recent research from the Max Delbrück Center identifies isopropyl myristate (IPM) as the compound responsible for this social control, which effectively alters hormonal states in other females to uphold a eusocial hierarchy.
Identifying the Chemical Marker of Authority
In a discovery that helps explain a “longstanding mystery” regarding naked mole-rat social structures, researchers at the Max Delbrück Center in Berlin have identified the mechanism by which queens maintain exclusive reproductive rights. The study is a “game changer,” says Melissa Holmes, a behavioural neuroscientist at the University of Toronto, Canada. To find the source of this social order, Mohammed Khallaf, a neuroscientist at the Max Delbrück Center for Molecular Medicine in Berlin, and his colleagues swabbed naked mole-rats of different social ranks to determine the odour chemicals they produced.
The team found that queens produce high levels of isopropyl myristate, a compound widely used in cosmetics as an emollient, emulsifier, and skin-penetration enhancer. This compound was found in abundance in queens and was almost entirely absent from other colony members. As reported in the study, the production of this chemical fluctuates in tandem with the queen’s own reproductive cycle, reaching its highest concentration during ovulation. “I got very excited when we found this compound that’s only produced by the queen,” says Khallaf.
While most female naked mole-rats in a colony have the biological potential to become queens, they are typically kept in a “stalled puberty phase,” says Lisa Stowers, a neuroscientist at Scripps Research in San Diego, California. These females’ reproductive organs are underdeveloped, and levels of the hormone prolactin are elevated.
Gary Lewin Links Olfactory Neural Pathways to Hypothalamic Hormone Regulation
Biological Circuitry and Hormonal Suppression
The scent does more than simply mark the queen; it actively alters the physiology of the subordinates. The study found that exposure to the queen’s scent is associated with increased levels of prolactin and decreased progesterone in subordinate naked mole-rats, which may help explain their infertility, though it is not yet clear if isopropyl myristate alone is responsible for these hormonal changes. This chemical communication relies on the animals’ highly developed sense of smell. Naked mole-rats have approximately 1,200 olfactory receptor genes, which enable them to detect a wide range of scents, including the compound emitted by the queen, according to Dr. Gary Lewin, group leader of the Molecular Physiology of Somatosensory Perception lab at the Max Delbrück Center.
For more on this story, see How Queen Odors Control Reproduction in Eusocial Mammals.
“When you activate these neurons, they connect to the olfactory cortex, which is where you process smell, but there must also be connections to the hypothalamus, and the hypothalamus is the brain region that controls hormonal state,” says Lewin, who has studied the biology of naked mole-rats for nearly 20 years. While the exact receptor responsible for binding isopropyl myristate remains unidentified, the existence of this specific pathway suggests a biological adaptation unique to the species. Brain imaging showed that exposure to IPM stimulated olfactory neurons in non-breeding females, suggesting that these individuals react to the chemical’s scent. To pinpoint the effects, the team removed some non-breeding females from the colony and used a drug to block the ability to smell in others. In both instances, the mole-rats’ levels of prolactin dropped, enabling those that were paired with males to mate.
Eusocial Colonies Employ Isopropyl Myristate to Block Subordinate Mating
Eusociality and Behavioral Consequences
The behavior of naked mole-rats draws clear parallels to the social structures of insects like bees, where the queen bee is the reproductive heart of the colony. In both species, a single breeding queen sits at the apex of the hierarchy, supported by a caste of workers who gather food and protect the colony. This eusocial arrangement is extremely rare among mammals. Typically, a male and female naked mole-rat will begin mating within a few days if separated from the colony. However, if isopropyl myristate is applied or bedding with the queen’s scent is introduced, mating does not occur. “There’s some sort of circuit that goes from the nose through the brain to the cortex and to the hypothalamus, and that must be a circuit that is pretty unique to naked mole rats,” says Lewin.
Subordinate Mole-rats Remain Infertile Through Continued Exposure to Residual Queen Scent
This hierarchy helps prevent rivalries within the group, ensuring a stronger foundation, higher survival rates, and greater harmony in the colony. Even when the queen is absent, the scent—though odourless to humans—remains effective on exposed mole-rats.
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