How does a single queen keep an entire society in check? In naked mole-rats, the nearly hairless rodents of East Africa, the answer is a smell. An international team led by the neurobiologist Gary Lewin at the Max Delbrück Center (MDC) in Berlin reports in the journal Nature that a colony's queen emits a volatile compound called isopropyl myristate — and with it renders every other female temporarily infertile.
Naked mole-rats are among the few mammals that, like bees or ants, live in fixed colonies. Only one female, the queen, reproduces; the rest dig tunnels, gather food and raise the young. How the ruler enforces her monopoly had long been a puzzle. That scent might play a part seemed plausible, since naked mole-rats can tell members of their own colony from strangers by smell.
Using mass spectrometry, the researchers identified the substance that only the queen gives off. Isopropyl myristate is odourless to humans — but the mole-rats perceive it well: with functional ultrasound, the team showed that specific brain regions in the animals respond to the compound. In the bodies of the queen's companions it raises levels of the hormone prolactin, which dampens fertility, while keeping progesterone low. As a result, no female except the queen remains able to conceive. How much of the compound she produces varies with her reproductive cycle.
That the scent alone suffices was shown in a striking experiment. When a queen dies, violent fights and mating usually break out within days. But when the team sprayed isopropyl myristate into a queenless colony every day, calm prevailed — the contest over succession simply did not happen. Only when the treatment stopped did the unrest return.
Why this is more than a curiosity
"A game changer," says the behavioural neuroscientist Melissa Holmes of the University of Toronto, because the study resolves a long-standing mystery: why only one female in a colony bears young. The others are stuck, as the Scripps researcher Lisa Stowers puts it, in a kind of stalled puberty.
Naked mole-rats are of great medical interest anyway: they live unusually long for rodents — up to 30 years — almost never develop cancer and feel little pain. About 450 of them live at the MDC in reconstructed tunnel systems. That their complex social order can be traced to a single molecule now opens a new route into the question of how smells steer behaviour and reproduction in mammals.