Mating. It’s a messy and time-consuming business. But at the moment, sexual reproduction is nature’s only option for those of us who want to pass on our genetic material with any degree of success.
But a population of female salamanders appears to have found a way out of the mating game. A paper published last month in the Journal of Zoology describes a self-cloning, all-female line that has maintained its genetic strength while evolving regenerative powers surpassing those of sexually reproducing peers.
Ambystoma salamanders live in North America, from southeast Ohio to Quebec. Within this species of dual-gendered, sexually reproducing amphibians is a lineage of unisexual animals. This means that they’re only one gender (in this case, female) and able to reproduce by cloning themselves.
Cloning is great for adding lots of new offspring to a population quickly. But species who reproduce that way tend to suffer over the long term for lack of genetic diversity.
“From an evolutionary perspective, the idea is if you don’t have sex, you don’t stick around very long over millions and millions of years because you don’t get that genetic variation,” said Robert D. Denton, a biology doctoral candidate at the Ohio State University and a co-author of the paper.
This all-girl clan of Ambystoma has found a work-around. Most salamanders mate externally—males deposit “sperm packets” for females to pick up. (Hot.) Through a mechanism science hasn’t completely worked out, unisexual salamanders are able to sidle over and steal DNA from these packets, in what Denton calls “sneaky sex.” The stolen genetic material triggers them to lay eggs virtually free of the unwitting sperm donors’ genes.
It’s a reproductive strategy known as “kleptogenesis”—essentially, reproduction by theft.
“On paper,” Denton said, “it’s the perfect way to reproduce: there are no males to take up resources, every female gets to pass on all of her genetic material, but they still get a new shot of genetic variation occasionally.”
This sperm-stealing crew also appears to be a super-charged salamander. When their tails were cut off, according to the new research, the unisexual salamanders regrew them 1.5 times faster than sexually-reproducing peers. Being able to regrow a tail quickly is a huge competitive advantage for Ambystoma, as it’s much better to offer predators an expendable limb than, say, a head.
A lot more research is needed to understand the relationship between these salamanders’ reproduction and their regenerative abilities, if there is one. But this all-girl salamander crew is such an evolutionary anomaly that researchers are intrigued.
“These animals are such an exception to the rule for how we understand vertebrate reproduction, so every piece to the puzzle is interesting,” he said.