Saturday, March 1, 2008

The Complex Eusocial System of the Naked Mole Rat

Eusocial animals are an anomaly within Kindgom Animalia because an individual will put its energy towards helping another reproduce instead of placing that energy towards the perpetuation of its own genes. Within a colony of naked mole-rats, only one female will mate with her few chosen consorts, and the young from previous litters maintain and defend the colony and assist in rearing newborns. They essentially sacrifice their own opportunities to survive and reproduce for the good of other colony members.

The naked mole-rats are the only known mammal to display this odd behavior. We see eusocial systems in Class Insecta, Order Hymenoptera: bees, wasps, and ants. Why be eusocial? The reason is that by helping the queen reproduce offspring, it may contribute more to future generations of the species than actually reproducing themselves.

Is eusociality altruistic? Certainly not. Guidelines governing eusociality are as follows:

1. Reproductive division of labor

2. Overlap of generations

3. Cooperative care of young

Naked mole-rats’ native range is in Kenya, Ethiopia and Somalia. They are exclusively fossorial, or underground, rodents that eat primarily the succulent tubers that are formed by many of the plant species that grow in arid areas. They obtain all the water they need through their food- they do not drink! When a group of mole-rats finds a large tuber, which may be more than a foot in diameter, they generally bore through it, eating mainly the interior flesh while leaving the thin epidermis intact. This behavior may allow the plant to remain healthy for some time- even to continue growing- thereby providing a long-term food resource for the colony.

(They also regularly practice coprophagy, the reingestion of feces, which allows them to maximize their uptake of nutrients from their food.)

"When the rains come, the eusocial mole rats cooperate and teams of animals dig like the fury," said Dr. Paul W. Sherman, a behavioral ecologist and Cornell professor of neurobiology and behavior. "Together, they are more likely than a solitary mole rat to find a bonanza of tubers to sustain the colony until the next rain. Alone, individuals would starve in that environment. And with a 'super mom' to produce more helpers, individuals willingly give up personal reproduction for indirect reproduction through relatives."

This video feature this odd rodent: hairless, with sensory hairs on their nose and tail (which allows them to move deliberately backwards and forwards) . Their large incisor teeth sit outside their lips so they can gnaw comfortably through the toughest tuber. They are adorable. Enjoy!

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