Five feet below the dry grasslands of Ethiopia lives a fascinating creature that seems to be breaking the rules of what it means to be a mammal. In a large colony more similar to that of ants or termites, this small, hairless, and virtually blind animal seems to avoid cancer, resist aging, and suffer from fewer diseases than other mammals. Despite living more like an insect than a mammal, the naked mole-rat (Heterocephalus glaber) seems to hold the secrets to many of our most yearned for biological possibilities. Might their unique social behaviours be connected to these remarkable physiological feats?

One scientist interested in precisely these kinds of questions is Dr. Phoebe Edwards, a researcher at the Social Neuroscience Lab at the University of Toronto Mississauga studying the naked mole-rat. When asked how she ended up working with these animals and in this area, Dr. Edwards explains: “I’m very interested in how the social environment can change physiology. We sort of think about physiology as being changed by things like food and physical exercise, but it can also be changed by observing behaviour from other individuals and [how they interact] with you.”

Naked mole-rats turn out to be the perfect subject for studying how specific social behaviours influence physiology because in the colony, not all members do the same thing. Naked mole-rats are one of only two mammal species that live eusocially (the other being the Damaraland mole-rat): only one female breeds — the Queen — and the rest of the colony ‘subordinates’ collectively care for all the pups, and maintain and/or defend the colony. Interestingly, as only the Queen and a select few males breed in the colony, the remaining subordinate mole-rats of both sexes are sexually immature. This division of labour allows researchers to compare physiology between members of the same colony that are exposed to different social environments and behaviour.

In a recent study, Dr. Edwards and her colleagues investigated a phenomenon observed in naked mole-rats that suggested that the social environment was contributing to visible physiological changes in the colony members. When the Queen was pregnant (an environmental change), other non-breeding individuals seemed to experience bodily changes themselves.

“It would almost be like the subordinates were going through puberty!” says Dr. Edwards, adding that this was unexpected and an usual response in mammals.

Some developed larger nipples, others showed vaginal perforation; all of them showed increased levels of the sex hormone estradiol. These are physiological changes involved in sexual maturation or pregnancy. But these non-breeding members usually don’t sexually mature at all. Something was clearly going on.

Dr. Edwards was skeptical of a previous hypothesis that proposed these physical changes might happen as the naked mole-rats eat the pregnant Queen’s poop and ingest her hormones. Although these animals do practice “coprophagia” – the ingestion of feces, “it felt unreasonable [that] the subordinates are eating that much feces to basically dose themselves [with hormones],” she explains. To test the idea that subordinates could possibly be ingesting hormones orally and other hypotheses, she injected one single subordinate mole-rat with estradiol (the suspected hormone at play) and monitored changes in the colony.

“My thinking was, if you dose any single animal in the colony with hormones, it should pass to the others.” – if in fact they are eating each others’ poop and getting estradiol that way.

But that didn’t happen, and the study concluded that although the exact mechanism was not yet known, hormone-transfer happening through feces, urine, or skin-contact was unlikely. Instead, it’s still possible that the changes in social environment that followed the queen’s pregnancy were triggering physiological changes in the rest of the colony. This is an intriguing prospect and further study of this species might inform our understanding of how our own species’ highly social nature might interact with individual physiology.

I wanted to hear her thoughts on a similar phenomenon in humans that I had anecdotal evidence of. “What about the old wives’ tale of women suddenly finding their menstrual periods syncing with others around them? Could that be a human example of this kind of social hormone sharing?” I ask Dr. Edwards.

“I’m glad you brought that up!” she responds, before sharing that this phenomenon, colloquially called the McClintock effect in psychology, is “pretty much debunked”. The results of the original 1971 study in support of the effect, by Dr. McClintock herself, have in later years been re-evaluated. It turns out the synching effect found in the study wasn’t significant, “no more than from random chance,” Dr. Edwards clarifies.

However, the results of a different paper, published last year (and in fact co-authored by Dr. Melissa Holmes, the principal investigator in Dr. Edwards lab at UTM) suggests yet another fertility-related reason to continue studying this species. Against the standard of virtually all other mammals, naked mole-rats don’t seem to experience any significant age-related decrease in fertility. Menopause, from the Greek for end of the moon (cycle), is experienced by most humans with ovaries in their 40s and 50s. Dr. Edwards explains, “as we get older, we have fewer and fewer eggs” — menopause marks the end of the fertile period and is initiated as the last eggs die.

For naked mole-rats, however, “they seem to just keep going, which is very rare,” adds Dr. Edwards. The vast majority of mammals experience reproductive senescence, ie. their chance of successful reproduction decreases with age. For mole-rats, the effects of this aging process seem negligible, and they can successfully conceive, carry, and deliver healthy pups their entire lives. This is an impressive feat, and a better understanding of the mechanisms behind this ability in naked mole-rats might eventually lead the way to extending human healthy reproduction spans and solve other problems of fertility.

Although the mystery of their pregnancy-related hormone sharing remains unsolved for now, researchers, including Dr. Phoebe Edwards will continue to study the remarkable naked mole-rat and what it might teach us about health, physiology, and the role of the social environment in biology.