People visiting The Fragile Desert love them or find them gross---either way, the naked mole-rats elicit some kind of comment from nearly everyone who walks past.
Naked mole-rats, surprisingly, are not much like their name suggests: they are not naked, they are not moles, and they are not rats. Instead, they are small (slightly bigger than mice) nearly hairless rodents, who have a very unique lifestyle. In the wild, naked mole-rats live in large colonies underneath the African desert. The colonies may be made up of several hundred animals, with a single breeding female---called the queen---and one to three breeding males. If you know anything about bees, you will realize that this set-up is common in the insect world, but is kind of unusual among mammals.
Who Will Be Queen?
Unusually, Brookfield Zoo’s colony of 30 animals actually had two queens: the original queen and a less dominant queen. This has been reported at other zoos, but keepers are not sure if it happens in the wild. Of course, studying animals that live underground isn’t easy, so just because it hasn’t been reported doesn’t mean it hasn’t happened!
Here at the zoo, this colony hadn’t successfully raised pups during the time when both queens were living, so maybe the role of queen was in flux. Recently, the original naked mole-rat queen passed away at age 18---living much longer than the average lifespan of 13 years.
How do we know who is battling to be queen? One way is to look at their size; queens grow and elongate when they become reproductively active, and their backbone grows more pronounced—traits that are less obvious in the remaining queen. In the past, the two queens had battled for the privilege of ruling the colony and for breeding rights. During a battle, the mole-rats will push each other, trying to shove the weaker animal backwards. Fighting occurs face-to-face…a position these diggers do not usually occupy.
The original queen had come to Brookfield Zoo in 1989, and in the course of her life had 45 litters, producing more than 580 naked mole-rat pups! Queens keep the other females from breeding through a nifty trick of nature: reproductive suppression.
Interested in their unusual behaviors, Brookfield Zoo conservation biologist Dr. Sue Margulis did a behavioral study several years ago to determine if a queen can tell which females will become the next queen. Being able to predict this would increase the chance of setting up other successful breeding colonies. Dr. Margulis worked with keepers to observe the animals and undertake hormone studies.
Queen of All
Life Below the Surface
Brookfield Zoo is home to six colonies of naked mole-rats. The largest colony can be seen in their glass tunnels, crawling, digging and climbing---behaviors that are very important to naked mole-rats. It might be a bit difficult to figure out which way they are going, because naked mole-rats can move as quickly going backward as they can going forward!
Like reptiles, naked mole-rats are not able to regulate their body temperature very well (they do not have much body fat, nor hair). To stay warm, they huddle together, spending time on top of, underneath, next to, and generally all over each other. Colonies of naked mole-rats can excavate enormous amounts of dirt, creating extensive caverns underground. Like everything they do, the excavation requires a lot of teamwork. They set up excavation assembly lines---with the front animals breaking through the dirt, while a string of workers sweep the soil through the tunnel system to an opening to the surface. The last worker kicks the dirt up onto the ground above its head, forming a mole hill. The mole-rats’ loose skin helps them squirm on top of and around each other, without getting stuck.
The result: the queen was most aggressive toward females that began to show characteristics (hormonally and behaviorally) of becoming queens; once the original queen or the high ranking female was removed, these females potentially could become queen. We also removed some females and placed them with males; those that showed behavioral and hormonal characteristics similar to the queen prior to their transfer out of the original colony eventually became queens of their own colonies.
Now that the new queen is in place, keepers are curious to see what will happen. Will she maintain her position as queen, or will another female try to usurp her? Will she begin to breed? Will the other animals show signs of increased aggression?
The answers will only come to light as Brookfield Zoo’s keepers and scientists keep their eyes underground and try to discover the naked truth about the world of naked mole-rats!
Check out some members of the colony going about their daily business. If you do not have Quicktime for Mac or PC, click on the tile below for a speedy download.