As one of only two mammal species to exhibit eusociality, the naked mole-rats have received lots of attention from the scientific community and are well known for their inability to feel pain, extremely long lives, resistance to cancer and, of course, their sheer ugliness. In fact, the naked mole-rats are so bizarre that they were placed in their very own Family (the Heterocephalidae) due to their divergence from their nearest living relative taking place over 31 million years ago! However, what you may not know is that naked mole-rats exhibit a dietary practice which somehow makes them even less appealing: coprophagy – the act of eating poop. Gross.
Restricted to their complex tunnel systems in desert environments of Eastern Africa, naked mole-rats are severely limited when it comes to what’s on the menu, with root tubers and plant bulbs making up the majority of their diet. These food sources are notoriously difficult to digest and thus require two full passages through the digestive system for nutrients to be fully absorbed. However, this may not be the only advantage to coprophagy in the naked mole-rat…
Colony structure of the naked mole-rat consists of one reproductively dominant queen and the few males with which she mates. The rest of the colony is made up of infertile, subordinate female workers which carry out tasks such as tunnel digging, colony defence, maintenance of chamber cleanliness and rearing the pups produced by the queen.
Pregnant naked mole-rat queen (centre) surrounded by her subordinate workers.
A recent study by a group of Japanese researchers found that workers belonging to a colony whose queen had just given birth were most responsive to the recordings of crying rat pups when compared to other groups of workers. Furthermore, high levels of an oestrogen compound important for parenting, oestradiol, was found in worker urine and faecal matter, but only when the queen was pregnant. However, as a result of their infertility, the worker force is incapable of producing such hormones and should subsequently be useless when it comes to rearing their queen’s pups. However, this is not the case at all. So, what’s happening here?
As it so happens, naked mole-rat workers have specialised bathroom chambers which they share with their queen, meaning they may in fact be acquiring the hormones required for parental care by feasting on royal excrement. To test this hypothesis, the researchers fed groups of workers with either the faeces of an already pregnant queen or the faeces of a non-pregnant queen treated to express high levels of oestradiol and once again assessed worker responsiveness to pup crying. In both cases, the workers exhibited high levels of responsiveness upon hearing the cries of a distressed pup.
Such results suggest that coprophagy is not only important for adequate digestion of food sources but also plays a major physiological role in providing workers with the necessary hormones for effective parenting of the queen’s pups, leading to more successful colony life.