Thereâs one scent to rule them all â and we now know what it is. A series of experiments has shown that a single molecule released by the queen of naked mole rat colonies prevents all the other females in a colony from breeding.
âItâs a super-contraceptive, if youâre a mole rat,â says at the Max DelbrĂźck Center in Berlin.
Naked mole rats (Heterocephalus glaber) have a social structure like that of bees and ants, with colonies made up of soldiers and workers, and a single queen ruling each colony. Only the queen can breed, but how she maintains her long reign â Lewinâs teamâs oldest queen is 39 â hasnât been clear.
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âThe theory was that the queen is larger and more aggressive than the other animals, exerting her dominance through pushing and shoving,â says Lewin. âBut we never found that very satisfying as an explanation.â
So team member , also at the Max DelbrĂźck Center, proposed identifying the mole rat bouquet â the molecules in the air around them that create their scent. Comparing the scents of hundreds of animals revealed that only the queens produce a molecule called isopropyl myristate.
âItâs made in the reproductive organs, basically the vagina of the reproductive female,â says Lewin.
When the team sprayed isopropyl myristate daily into cages containing male and female pairs, none of the females became pregnant. Without it, almost all the females became pregnant.
Next, the team removed a queen from a colony and applied isopropyl myristate daily. There were no fights for succession and no females started breeding during the three months this was done. âWe produced peacefulness,â says Lewin. âThatâs probably the most dramatic experiment.â
When the team stopped applying isopropyl myristate, the high-ranking females started fighting within a week. After around three weeks one became pregnant: the new queen.
The team also showed that exposure to isopropyl myristate changes the levels of the hormones progesterone and prolactin. But they havenât found out exactly how the molecule is detected and leads to these changes â thatâs the next project, says Lewin.
The evidence for isopropyl myristate influencing reproduction is compelling, says at Linnaeus University in Sweden. âI think itâs an impressive and important study. And convincing.â
at Queen Mary University of London is also convinced. âBut the paper raises many questions, like any interesting research,â says Faulkes. These include how animals detect it, and how behavioural interactions and queen dominance interact with the scent, he says.
There is something special about isopropyl myristate, says Lewin. Isopropyl myristate is volatile, meaning it can evaporate into the air, but itâs not highly volatile, so any traces left by the queen take time to evaporate and the scent persists for at least a day.
Itâs known that a queen will patrol every part of her colony, which in the wild might extend underground for 3 kilometres. âWe think the reason she does that is to deposit this molecule around the colony,â says Lewin. âTo make sure that every member of her colony is exposed to her scent.â
Other experiments by the team suggest the animals can consciously detect the smell. For instance, highly ranked females with a chance of becoming queen try to avoid places where isopropyl myristate is present, whereas lower-ranked animals arenât bothered.
The team also tested a number of other species of mole rat. They didnât find isopropyl myristate in any solitary species but they did find it in a few species whose social structure is more like that of naked mole rats. âBut I would be cautious about assuming that the same pathway has a comparable function across social mole rats without direct experimental evidence,â says ZĂśttl.
Isopropyl myristate is also widely used in cosmetics. It is described as odourless but Lewin says some women at his lab thought they could smell something when exposed to it. A 2008 study also reported that during pregnancy and after childbirth.
Nature
