Workaholic Naked Mole Rats

Why do naked mole rats interfere with the work of colony-mates?

Posted Jan 24, 2019

Meghan Murphy, Smithsonian’s National Zoo, via Flickr. Distributed under a CC BY-NC-ND 2.0 license.
Naked mole rat.
Source: Meghan Murphy, Smithsonian’s National Zoo, via Flickr. Distributed under a CC BY-NC-ND 2.0 license.

In the wild, naked mole rats dig a complex tunnel system, complete with chambers for different purposes, covering several hundred meters. It’s hard work, but they accomplish it together. So why do naked mole rats sometimes interfere with the work of their colony mates via a behavior scientists call “tail-tugging?”

Naked mole rats spend their lives underground in groups consisting of two to more than 200 closely related colony members. Each colony has a single reproductive queen who, with the help of one to three breeding males, produces all the pups. Other colony members are subordinate, non-reproductive workers who help care for pups and perform other work, such as digging tunnels.

While digging, naked mole rats will sometimes interfere with the work of other individuals by tail-tugging: holding the tail of a colony member in the mouth and pulling that individual to another place.

Nobuyuki Kutsukake, used with permission.
Tail-tugging in naked mole rats.
Source: Nobuyuki Kutsukake, used with permission.

Nobuyuki Kutsukake, a lecturer at Sokendai (The Graduate University for Advanced Studies), Japan, noticed this behavior in the captive naked mole rats he was studying while a post-doctoral researcher at RIKEN Brain Science Institute, Japan.

“It remains puzzling why individuals interfere with another individual’s work even though the work that is being done must be beneficial for the whole colony, including the actor in the tail-tugging,” he wrote in a recent paper in the Journal of Ethology.

Kutsukake and his colleagues decided to analyze tail-tugging in naked mole rats in light of three hypotheses: 1) tail-tugging could reflect aggression; 2) it could be performed to ensure smooth turn-taking during work; or 3) it could serve to remove a colony member from a preferred workspace.

Behavioral observations revealed that tail-tugging is performed and received by individuals of all social categories. A queen in one colony doled out the most tail-tugs, contributing to 72.5% of the observed bouts. But another colony’s queen was never observed performing tail-tugging. Additionally, the tail-tugger was not always heavier than the recipient, suggesting that the behavior does not always follow dominance rank.

Of the three hypotheses, the behavioral data best support the third hypothesis: Tail-tugging is intended to remove a colony member from a preferred workspace so the tail-tugger can work there.

Meghan Murphy, Smithsonian’s National Zoo, via Flickr. Distributed under a CC BY-NC-ND 2.0 license.
Source: Meghan Murphy, Smithsonian’s National Zoo, via Flickr. Distributed under a CC BY-NC-ND 2.0 license.

Kutsukake says it is likely that tail-tugging is used to monopolize work in a specific place. The behavior was related to the work context, occurring most frequently during work and in locations where the tail-tugger tended to perform work more frequently.

The question remains as to what advantage is gained by monopolizing a workspace. Work like digging is costly and beneficial for the whole colony, so why would a naked mole rat stop another colony member working toward the same purpose?

Kutsukake speculates that tail-tugging is a side effect of the naked mole rat’s cooperative tendencies.

“This species really likes to work and cooperate for the colony,” he says. “My guess is that tail-tugging is a negative by-product caused by the genetic and physiological underpinnings of their extremely cooperative behavior.”

In other words, naked mole rats want to work for the good of their colony so much that they are driven to interrupt fellow workers doing the same work.

Naked mole rats are a eusocial species, like many ants and bees. All colony members work together to raise the queen’s pups and maintain the tunnel system. Their cooperative tendencies have been selected for over evolutionary time and are ingrained. This might result in a drive to work so strong that they will tail-tug other colony members out of the way.

References

Kutsukake, N., Inada, M., Sakamoto, S. H., and Okanoya, K. (2019). Behavioural interference among eusocial naked mole rats during work. Journal of Ethology. Doi: 10.1007/s10164-018-0581-9.

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