Naked mole rats might be fascinating animals, but they also resemble the old, crusty men that inevitably make your trip to the nude beach regrettable. Now new research has shown that these hideous rodents also have the world's most deformed, sluggish sperm, according to New Scientist.
In other words, the sperm look a lot like the animal. Scientist Liana Maree of the University of the Western Cape in Bellville, South Africa, found that only 7 percent of naked mole rat sperm even moved. The sperm that did move clocked in at around 35 micrometers per second-- the slowest of any mammal in the world.
So why the shriveled sex cells? Maree suspects the prime culprit is a lack of sexual competition within naked mole rat society. "The reason they look so ugly and swim so slowly is there is no sperm competition," she said.
Naked mole rats are unique among mammals in that they live in an insect-like society where a single queen dominates and performs all the reproductive work. She chooses only one male at a time to breed with, and is capable of suppressing the reproductive drive of all the other males to encourage cooperation rather than competition. As a result, the one lucky male chosen as breeder can afford to have sperm that flaccidly lollygags its way to the egg.
"It just goes to show how very important sperm competition is as an evolutionary force acting on sperm form and function," said Matthew Gage at the University of East Anglia in Norwich, UK.
Researchers did note that the sperm they sampled came from naked mole rats held in captivity, but they were careful to ensure that the colony they sourced sperm from was not inbred.
Aside from now being known as the mammal with the ugliest sperm, naked mole rats are also known for being the only mammals in the world that don't get cancer. They also lack pain sensation in their skin-- an adaptation to their harsh, burrowing lifestyle-- and are completely blind (perhaps for the best, given their looks!).
"The naked mole rat is actually a very good model for what happens in humans," added Maree.
Studies have found that more promiscuous primates typically have stalwart, faster swimming sperm compared to monogamous species. Since humans tend toward monogamy, our sperm is likewise less virile. But don't worry, guys: at least 60 percent of our sperm is active, as opposed to the meager 7 percent of the naked mole rat.