The ancient Greeks spoke of a mythological society composed entirely of warrior women. The medieval traveler John Mandeville wrote of a place whose female rulers "never would suffer man to dwell amongst them." "Paradise Island," home of Wonder Woman, was a feminist utopia where no one with a Y chromosome was allowed.
"They’re pretty incredible," said Robert Denton, a biologist at Ohio State who studies an unusual group of salamander species that literally don't need men.
These creatures – all female – reproduce by cloning themselves. To keep their gene pool diverse, they sometimes "steal" sperm left behind on trees and leaves by male salamanders of other species and incorporate that DNA into their offspring. Most sexually reproducing organisms have two sets of chromosomes to make up their genome – one from each parent. But one of these strange salamanders can have between two and five times that much genetic material lying in wait within her cells. It's as if they have multiple genomes to fall back on, and that's made them incredibly successful. "Polyploid" salamanders have been around some 6 million years, Denton said — far longer than most other animal species that reproduce asexually. Since a lack of diversity means having a smaller arsenal of genetic variation to fall back on when living conditions change, these groups usually go extinct relatively quickly.
In fact, these Amazon Women salamanders seem to be better off than their heterosexual counterparts in some respects. In a new study published Monday in the Journal of Zoology, Denton and his colleagues report that the all-female salamanders they studied could regenerate lost limbs 36 percent faster than other species.
If you're living in an Ohio swamp, it seems, you're better off without men.
The study was conceived by Monica Saccucci, now a medical student at the University of Cincinnati. At the time, though, she was still an undergrad working in the same lab as Denton.
First, Saccucci went into the wetland near Ohio State to collect eggs from both polyploid and ordinary members of the salamander genus Ambystoma. Once they'd all reached adulthood, she cut off 40 percent of each salamander's tail to see how fast it would grow back. Ambystoma salamanders, like many amphibians, are masters of regeneration.
But the polyploid salamanders were the queens of them all. Within 10 weeks, they had brand new, full length tails. Their sexually reproducing cousins, on the other hand, weren't finished regenerating for another five weeks.
It makes sense that this might be the case, according to Denton. Polyploid creatures simply have more of the equipment necessary to build back what they've lost.
"More genomes means more genes which produce more RNA which make proteins and that causes a much faster pipeline to producing more tissue," he said.
This ability gives them a big leg up from an evolutionary perspective. Salamanders' tails serve more than mere decorative purposes: in the water, tails help them to swim, and on land they can use their tail to distract predators. Being able to regrow their tails in record time after they get snapped off by a predator or in a some kind of aquatic accident makes it more likely that the all-female salamanders will stay alive to reproduce.
"They get injured a lot," Saccucci said in a news release. "If you can't regenerate, you're dead."
Correction: An earlier version of this post incorrectly reported how quickly the tails of all-female salamanders grow back.
More animals that don't need a man: