Female naked mole rats gain maternal urges not by giving birth, but by chowing down on poo.
In colonies of naked mole rats (Heterocephalus glaber), only one female — the queen — bears young. Subordinate females care for the pups, although they cannot produce oestrogen and other hormones that stimulate motherly behaviour.
A team led by Kazutaka Mogi at Azabu University in Sagamihara, Japan, suspected that the females’ parental instincts might stem from their habit of eating the pregnant queen’s hormone-rich faeces. The researchers fed samples of this poo to her subordinates, and then played recordings of pups’ distress calls. The team also collected poo from a queen that wasn’t pregnant, added oestrogen to the faeces and fed it to subordinate females.
Females that ate hormone-laden poo from either of the queens were more likely than control females to respond to the pups’ calls. Further analyses showed that the repast had elevated the females’ oestrogen levels.
This unique form of behavioural activation might have evolved because odours and airborne hormones, which induce behaviours in some other animals, do not travel well in the rats’ underground tunnels.