National Geographic
Menu

Naked Mole Rat Sperm Revealed

Even lazy sperm can get the job done—at least if you’re a naked mole rat.

A new study shows the blind, tunnel-dwelling rodents have “dismal” and degenerate sperm, which sport irregularly shaped heads, poorly developed necks, and tails lacking the fibrous covering thought to power their movements, among other abnormalities.

Naked mole rats grooming. Photo courtesy Dr. Liana Maree

Scientists recently examined sperm from three social strata of the colony-living animals. They found no difference between the groups, and that only one to 15 percent of the sperm studied could swim. What’s more, only one percent of that active sperm were fast swimmers.

(Related: “‘Lazy Slob’ Mole Rats Are Key to Colony Growth, Study Says.”)

Why the lackluster performance? It may be because of the absence of male competition for female mole rats, study author Gerhard van der Horst, of the University of the Western Cape in South Africa, said in a statement.

In mole rat society, the queen mates with one to three males, and the rest of the colony serve as workers.

“Once the queen has picked her consort(s), she keeps the other females and males subordinate by using physical aggression. It seems that the resultant lack of competition between breeding males for the colony queen contributed to an overall decrease in sperm ‘fitness,'” van der Horst said.

(Read how sex can speed up evolution.)

In a surprising finding, the subpar sperm still fathered several healthy offspring, added van der Horst, whose study was published recently in the journal BMC Evolutionary Biology.

Naked mole rat sperm under the microscope. Photo courtesy Dr. Liana Maree

 

But sperm aren’t usually slackers, as our previous reporting has shown.

For instance, in March, scientists reported how men are able to produce 1,500 sperm cells a second (get the full story).

And in April, I reported that in promiscuous mouse species, sperm team up with their closest kin to give themselves an edge in the dash for the egg.

Once inside a female, sperm cells can discern and—via structures on their heads—literally hook up with their brethren amid the crush of sperm from other males.

“It’s really amazing that this single cell can do this,” Heidi Fisher, an evolutionary geneticist at Harvard University’s Hoekstra Laboratory, said in that story.

“We used to think of sperm as packs of DNA with really fast tails. But [now we know] they’re able to make these complex organizations.”

More sperm news:

Get more weird news at National Geographic News.