Some naked mole rats are designated toilet cleaners, study suggests
Naked mole rats may play specific roles, including “toilet cleaners” and “trash collectors”, new research suggests.
The results, published Wednesday October 8 in the journal Scientific advancessuggest that naked mole rat colonies are even more complex than scientists previously thought.
Naked mole rats (Heterocephalic glaber) are small, almost hairless rodents that live in underground colonies of between 20 and several hundred individuals. They are one of only two mammal species known to be eusocialwhich means that they exhibit an advanced social organization, similar to that of bees or wasps. For eusocial mammals, the queen reproduces, while most other members of the colony – which can span several kilometers of tunnels – are sterile workers.
These workers perform a range of tasks, including soldiers, tunnel diggers, foragers and guards.
But it was unclear whether individuals changed jobs or tended to stick to specific roles. To investigate, Teruhiro Okuyamabehavioral neuroscientist at the University of Tokyo, and his colleagues created an artificial burrow in their laboratory. It was composed of nine chambers, each measuring 5.9 by 5.9 inches (15 by 15 centimeters), and arranged in a three-by-three grid. Adjacent boxes were connected by 6-inch-long (16 cm) pipes.
The mole rats designated different rooms for specific uses, including a nesting place, a trash area, a common “toilet,” and several compartments without specific functions.
Over 30 days, Okuyama and his colleagues studied five colonies, each containing about 20 individuals, by implanting microchips in the mole rats and installing detectors throughout the colony. This allowed researchers to constantly monitor where the animals went and which people they spent time with.
They found that the breeding animals – the queen and a few males – stayed close to each other most of the time and followed each other.
But the workers, they discovered, could be divided into six groups based on their movements. “They were doing a different job if they weren’t reproducing,” Okuyama told Live Science.
One group moved around a lot and spent the most time in the dumpster. Okuyama therefore speculated that they may have been transportation specialists. Another group primarily occupied the toilet room, so the researchers proposed that these individuals might be cleaners.
A third group was less active and generally stayed in the nest box. These were often younger animals or individuals that were older and perhaps past their prime. “I think the work gradually evolves with age,” Okuyama said.
Complex colonies
By revealing that naked mole rats might have distinct roles outside of breeding or generic work, the work highlights how their social organization might be much more complex than we thought, he added.
“It’s a really interesting study” Chris Faulkesan evolutionary ecologist at Queen Mary, University of London who was not involved in the work, told Live Science. “Anyone who has spent time observing naked mole rats will agree that there are many individual things going on and that some animals will spend a lot of time in the toilet, sweeping or digging. This is a good attempt to further quantify these complexities.”
However, Markus Zöttla behavioral ecologist at Linnaeus University in Sweden who was not involved in the work, said it was difficult to draw too many conclusions from the observations.
“This paper shows that there are variations in behavior between assistants. Some assistants are more active, others rest more,” he told Live Science. “But that’s what you would expect of any social animal. Some would be more proactive, some would be more socially aggressive, some would be more timid. Some people might call it an animal personality, and others would call it a caste system.”
We should also be careful about jumping to conclusions about what is happening in nature based on a relatively small and simple laboratory burrow with short tunnels, Zöttl noted. “If you consider the ecology of these species, a burrow can span the size of a football field,” he said.
Different behaviors could emerge in a complex natural burrow system with long tunnels in which animals must dig to find enough roots to feed dozens of colony members or more, rather than receiving food, he said.
As they travel through these long tunnels, the animals often establish their place in the social hierarchy by bumping into, interacting with, or avoiding each other as they pass through, Faulkes explained, which would then influence their behavior within the colony. However, he continues to believe that laboratory work brings us new knowledge.
“There’s this hidden behavioral complexity, and you have groups or individuals doing very different things and interacting in different ways within the colony,” he said.
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