The Amazons were a mythical race of warrior women who, in one version of the story, removed their right breasts to be more hardcore. But an all-female race of salamanders doesn't suffer from missing body parts. In fact, these animals have super-powered regeneration: when they lose an appendage, they can grow it back much more quickly than other salamanders do. The secret lies somewhere in the salamanders' bizarre genetics. "They sort of defy definition," says Rob Denton, a graduate student in ecology at Ohio State University. The amphibians he studied aren't even a real species, to start with. They're an ancient lineage (like the Amazons) that can be traced back about 6 million years. Rather than the two sets of genes most animals have, these salamanders may have three or more sets. They're all females, and usually reproduce by cloning themselves. But they don't totally ignore males. They'll mate with males of other salamander species that happen to be nearby, and use the process to trigger their own egg production. Sometimes, sperm from one of these males "leaks" into the offspring, Denton explains. This new set of genes may be added to the next generation, or swapped in for one of its existing sets. The process is called kleptogenesis—creation by stealing. In two Ohio wetlands, Denton and his coauthors studied all-female salamanders that live alongside a more normal species called the small-mouthed salamander. Most of the all-female salamanders here have three sets of genes (one stolen from a species called the blue-spotted salamander, and two from the Jefferson salamander). The researchers scooped up blobs of eggs laid by both all-female salamanders and small-mouthed salamanders, then brought them back to the lab. After the baby salamanders had hatched and grown, the researchers snipped off—sorry!—the ends of their tails. This is a crisis salamanders are prepared for; they're experts at regrowing lost body parts. The researchers carefully watched and measured the salamanders (10 all-female and 30 small-mouthed) over the next few months. The race to regrow their tails wasn't close. It took small-mouthed salamanders almost 12 weeks, on average, to grow their tails back. It took the all-female salamanders less than 8 weeks. "It was amazing to see the tails grow back so quickly in front of our eyes," Denton says. "I don't think we expected the salamanders to show such a drastic difference in growth rate." The researchers weren't totally surprised by the results, though. Other animals that have extra gene sets—specifically, New Zealand mud snails—also have extra-fast tissue regeneration. It's not clear why, exactly, this is. There may be specific genes among the stolen complement that are good for tissue regrowth. But it's more likely that the actual number of gene sets is the key, Denton says. There seems to be a connection between having more sets of genes and more molecular machinery for rebuilding lost body parts. No matter how they do it, these ladies are legendary. Image: by Robert Denton.
Saccucci, M., Denton, R., Holding, M., & Gibbs, H. (2016). Polyploid unisexual salamanders have higher tissue regeneration rates than diploid sexual relatives Journal of Zoology DOI: 10.1111/jzo.12339