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Naked Mole Rats: The Animal Kingdom's Most Functional Dysfunctional Family

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The naked mole rat lives as bees or ants do — in a colony with a queen and soldiers.
Sabri Ben-Achour
The naked mole rat lives as bees or ants do — in a colony with a queen and soldiers.

Naked mole rats are very cute, in a very ugly way.

"They have very little hair, no fur, some whiskers, some hair between their toes, like hobbits, and actually some hair inside of their mouth, which keeps their mouth nice and clean while they dig because they dig with their teeth, says David Kessler with the Smithsonian's National Zoo. "They're virtually blind 'cause they spend their entire lives underground, their skin is very thin and wrinkly, and almost translucent."

The teeth are gruesome, frankly. They stick out through the lips, the top pair coming out just below the nostrils. Naked mole rats can chew through concrete and bite through a human hand. They spend their lives burrowing beneath the East African dirt in search of giant tubers and roots.

They are fleshy and pinkish gray. They look and feel like the back of your elbow. They live like ants or termites or bees, with a queen and worker mole rats, some soldier mole rats, and a couple of breeding males.

And they helped solve a mystery that dated back to Darwin's day.

The mystery of the hive

When Darwin published his seminal work "The Origin of Species," he devoted a chapter to problems with the theory.

"He brought up queens and workers in honeybees," explains Stan Braude at the University of Washington. "How could you get different morphs of workers if the workers were sterile?"

Though there was no name for it at the time, Darwin was talking about eusociality, the communal living and division of labor so often seen in termites, ants and bees. From Darwin's perspective, the sterile worker and soldier was an enigma — how could you evolve into something that can't reproduce? If evolution is all about the survival of the fittest, worker bees or soldier ants would seem to be the least fit of them all — so impossibly unfit that they can't even reproduce!

Darwin hinted that the answer might be such a thing as natural selection between hives, so genes that were in the interest of the whole hive would get passed along because while they aren't great for individuals (worker bees can't reproduce), they are good for the hive as a whole (the hive works together to ensure everyone's survival, including the queen and mating males who do reproduce, some of their offspring being workers).

"The basic answer," explains Braude, "is that there are other venues to spreading genes like the genes for being a worker than just having offspring. If you spend your life producing lots of siblings, and then that can be more successful than spending your life producing a smaller number of offspring."

And if you're the queen, Braude argues, it's in YOUR interest to have helpers ensure the survival of your babies, babies who could one day split off to start new colonies.

Early theorists, most notably W.D. Hamilton, thought that maybe the hive mentality came about because of a high degree of genetic relatedness among insect families. He pointed out that because of the way termites, bees, and ants reproduce, female siblings share much more DNA (75 percent for bees, wasps, and ants) than do siblings of other types of animal (50 percent). Because they share so much DNA, they are more likely thought Hamilton, to sacrifice their own reproduction for that of a sibling or parent. If a sibling helps raise a bunch of sisters who reproduce, that will spread as many of her genes as having kids would. It was believed that the hive only existed among ants, termites, and bees because of their high degree of relatedness.

Enter the mole rat

In the 1970s, Richard Alexander had another idea. He agreed with many scientists on the basic mechanism behind eusociality -- that individuals could spread their genes by helping family members reproduce -- or getting family members to help them reproduce. But he saw a more structural explanation.

Braude, who was Alexander's student, explains it this way:

Bees, wasps, and ants "are unique among insects in that they are extremely parental... Alexander argued if you're already parental, you take care of your young, feed and protect them, then all it takes to be eusocial is change the timing when you start expressing these behaviors." If you start acting like a parent before you start making your own eggs — guess what, you're a worker!

It was quickly pointed out that birds and mammals are very parental, but do not live in hives. In a series of lectures, Alexander listed what else it would take to get a eusocial mammal. From a paper Braude authored back in 1997:

Alexander predicted that a eusocial vertebrate's nest should be (1) safe, (2) expandable, and (3) in or near an abundance of food that can (4) be obtained with little risk. These characteristics follow from the general characteristics of primitive termite nests inside logs. The nest must be safe or it will be exploited as a rich food source for predators. It must be expandable so that workers can enhance the value of the nest. It must be supplied with safe abundant food so that large groups can live together with little competition over food or over who must retrieve it.

The limitations of the nest characteristics suggested that the animal would be (5) completely subterranean because few logs or trees are large enough to house large colonies of vertebrates. Being subterranean further suggested that the eusocial vertebrate would be (6) a mammal and even more specifically (7) a rodent since many rodents nest underground. The primary food of the hypothetical vertebrate would be (8) large underground roots and tubers because the small grassy roots and grubs that moles feed on are so scattered that they are better exploited by lone individuals and would inhibit rather than encourage the evolution of eusociality.

The major predator of the hypothetical vertebrate would have to be (9) able to enter the burrow but be deterred by the heroic acts of one or a few individuals. This would allow for the evolution of divergent life lengths and reproductive value curves between workers and reproductives. Predators fitting this description would include snakes.

Alexander went on to predict the type of clay, region and habitat of Eastern Africa. A researcher by the name of Jennifer Jarvis noted how Alexander was basically describing a mole rat down to the detail. Nobody knew mole rats were eusocial, but after investigating they turned out to be the first species of eusocial mammal ever discovered. There are two other types of mole rat, which have since been discovered to be eusocial as well as a type of shrimp.

In this way, mole rats expanded science's understanding of what drives one of the most amazing, and previously puzzling, phenomena in nature.

[Music: "We Are Family" by The Chipmunks from The Squeakquel]

Photos: Naked Mole Rats


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