Eating queen’s poop makes naked mole rats babysit her kids | Science News for Students

Eating queen’s poop makes naked mole rats babysit her kids

The scat contains a hormone that transforms other females into nannies
Sep 25, 2018 — 6:45 am EST
a naked mole rat eating

As in a honeybee hive, the queen in a naked mole rat colony is the only mom. She gives birth to all of the young. But she’ll need child-care help for all her babies. And she’ll get it from the other females, especially if they’ve dined on her poop, new data show.

Kevin McGee/Flickr (CC BY-NC-SA 2.0)

Dealing with poop is a major part of raising children, regardless of the species. But it’s especially important for naked mole rats. A mom’s poop actually encourages other females in her colony to help with her child care, new data indicate.

Naked mole rats are small, nearly hairless rodents native to East Africa. They live in large underground colonies. A single queen in each colony gives birth to a few dozen pups each year. But she doesn’t care for those babies alone. Other females help her out. These nannies get their cues on when they’re needed from their diet — the queen’s poop. That’s the finding of a new study.

Many females share a colony. Only one of them — the queen — reproduces. Ovaries, a reproductive organ, never develop in the other females. So they can’t bear young. Their job, most of the time, is to find food and defend the colony. But when a queen becomes a mom, those other females assume an additional role: babysitter. They groom the babies and keep them warm. They also respond to crying and make sure the pups stay in the nest.

In other animals, hormone changes during pregnancy usually serve as cues for such nurturing. Except for their queen, female naked mole rats don’t experience those changes. Yet they still care for her babies.

Kazutaka Mogi works at Azabu University in Sagamihara, Japan. This developmental biologist was part of a team that explored what might cause these females to become her brood’s babysitters. They focused on one of this species’ most unusual foods: dung.

Feces contain partially digested food. That’s why naked mole rats regularly eat each other’s poop. It allows these rodents to extract additional nutrients initially left behind in the wastes. The feces of a pregnant queen contain high levels of one female sex hormone — estradiol (Ess-truh-DY-awl).

Mogi’s group looked to see if it was what made the other females act like moms.

a mole rat burrow with several baby mole rats and at least one adult mole rat
The poop of a queen naked mole rat contains the hormone estradiol. Eating poop laced with that hormone appears to encourage other females to care for her young.  
Ltshears/Wikimedia Commons

They started by collecting poop pellets from nonpregnant queens. They added estradiol to half of the pellets. This would mimic those shed by pregnant mole rats. Then the scientists fed plain and hormone-treated pellets to female mole rats for nine days.

Those eating the treated feces excreted more estradiol in their own dung. That showed that dining on the hormone-packed poop can change her own hormone levels. And mole rats that had done this were more responsive to a pup’s cries than were females that ate poop without the hormone boost.

Mogi studies how animals change and grow at different stages of their lives. The queen’s poop may not be directly shared with the whole colony, he says. Instead, those that spend the most time in her nest are probably the ones that eat her scat. They may, in turn, pass estradiol down to other colony members through their own poop, he says.

His team shared its findings August 27 in the Proceedings of the National Academy of Sciences.

Power Words

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biology     The study of living things. The scientists who study them are known as biologists.

brood     A group of related animals that emerges in a specific region in the same year. Depending on the animal type, the collective group is sometimes also known as a year class. (verb) The act of guarding and/or incubating eggs.

develop     To emerge or come into being, either naturally or through human intervention, such as by manufacturing. (in biology) To grow as an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.

developmental     (in biology) An adjective that refers to the changes an organism undergoes from conception through adulthood. Those changes often involve chemistry, size and sometimes even shape.

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.

dung     The feces of animals, also known as manure.

estradiol     The primary female sex hormone, a type of estrogen. Produced throughout life in both males and females. Among adult women, it’s produced mostly by the ovaries, to help the body prepare for the potential to reproduce (have a baby).

extract     (v.) To separate one chemical (or component of something) from a complex mix. (noun) A substance, often in concentrated form, that has been removed from its natural source. Extracts are often taken from plants (such as spearmint or lavender), flowers and buds (such as roses and cloves), fruit (such as lemons and oranges) or seeds and nuts (such as almonds and pistachios).

feces     A body's solid waste, made up of undigested food, bacteria and water. The feces of larger animals are sometimes also called dung.

groom     (in zoology) The practice of some animals to clean another, usually in places the groomed animal can’t see or reach, such as the back, head or face. Sometimes a groomer will remove ticks or other parasites. Other times it might remove tangles in fur or debris such as leaves. The attention the groomed animal receives can be calming and is usually accepted only from a family member or close member of its social group.

hormone     (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body.

native     Associated with a particular location; native plants and animals have been found in a particular location since recorded history began. These species also tend to have developed within a region, occurring there naturally (not because they were planted or moved there by people). Most are particularly well adapted to their environment.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

ovary     (in animals) A female reproductive organ that produces eggs and that secretes some of the hormones needed to regulate the development of secondary sex-related traits (such as breast development in human females). Most female mammals have a pair of ovaries.

Proceedings of the National Academy of Sciences     A prestigious journal publishing original scientific research, begun in 1914. The journal's content spans the biological, physical, and social sciences. Each of the more than 3,000 papers it publishes each year, now, are not only peer reviewed but also approved by a member of the U.S. National Academy of Sciences.

pup     A term given to the young of many animals, from dogs and mice to seals.

rodent     A mammal of the order Rodentia, a group that includes mice, rats, squirrels, guinea pigs, hamsters and porcupines.

scat     The feces shed by a wild animal, usually a mammal.

sex     An animal’s biological status, typically male or female. There are a number of indicators of biological sex, including sex chromosomes, gonads, internal reproductive organs, and external genitals. It can also be a term for some system of mating between male and female animals such that each parent organism contributes genes to the potential offspring, usually through the fertilization of an egg cell by a sperm cell.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

waste     Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.

Citation

Journal: A. Watarai et al. Responses to pup vocalizations in subordinate naked mole-rats are induced by estradiol ingested through coprophagy of queen’s feces. Proceedings of the National Academy of Sciences. Published online August 27, 2018. doi: 10.1073/pnas.1720530115.