Self-Perpetuating Female Salamanders Are Better Off Without Males, Study Finds

Human sex is fascinating, but compared to other animals, the way we reproduce is boring. Take the mole salamander, for example. Some all-female populations of salamanders have figured out a way to make copies of themselves without bothering to involve males. Now, ordinarily, that kind of reproduction shrinks the gene pool and makes animals less able to adapt. But researchers, who published their findings in the Journal of Zoology, say the opposite is true for some mole salamanders, which have complex genes and can regenerate body parts faster than their relatives.

How could an all-female group add to its gene pool? Two words: secondhand sperm. Male salamanders in the genus Ambystona are sloppy creatures, and will leave pools of their genetic material lying around on leaves and twigs. If a female salamander happens to find that sperm, she might just put it to use. And it gets even weirder: that male doesn’t even have to belong to her species. A cloned female could carry DNA from several different species at once—and it’s this capacity that may make her special.

To learn more, researchers collected six blobs of salamander eggs from wetland environments in Ohio. Three of the egg masses were taken from populations of sexually reproducing male and female small-mouth salamanders (A. texanum). The other three egg blobs were collected from all-female (or unisexual) groups in the same area. All the eggs were brought back to the lab and their inhabitants reared to adulthood.

Denton palling around with one of his gifted subjects. Image Credit: Kevin Fitzsimmons, The Ohio State University

Once the salamanders were 10 to 12 months old, the researchers took them out and cut a small piece from each one’s tail. The tail snips from unisexual salamanders were used to test their DNA and identify their ancestry. Now humans, most other mammals, and many salamanders are diploid: that is, each individual has two sets of chromosomes, one from each parent. Salamanders from the no-boys-allowed club, on the other hand, had three sets apiece, taken from two different species (A. laterale and A. jeffersonium).

The researchers monitored the salamanders for weeks, measuring their tails to see if and how quickly they were growing back. A gap soon emerged. After seven weeks, the self-cloning salamanders’ tails were almost completely regenerated. But the small-mouths’ tails wouldn’t finish growing back for another four weeks after that. To put it another way: members of the all-female salamander group regenerated their tails 1.5 times faster than the small-mouths could.

"I don't think we expected it to happen so fast," Ohio State biologist and study co-author Robert Denton said in a press statement.

A salamander’s tail is not just for show; it’s a functional appendage. As juveniles in the water, salamander larvae need tails to propel them through the water in order to evade predators. As adults, they can use their tails to distract opponents long enough to get away. So the ability to grow back a tail quickly is kind of a huge advantage.

"They get injured a lot," said biology student and study leader Monica Saccucci. "If you can't regenerate, you're dead.”

Saccucci, Denton, and their colleagues are quite impressed with the unisexual salamanders, but remain unsure of how they’re doing it. Is having sex with yourself the key to getting ahead? Is it the fact that each salamander lady is a hybrid? Are their ancestral species just really cool? Is it all those chromosomes they’re hoarding?

"Ideally, we'd love to compare unisexuals with different numbers of genomes from different species against those sexual species," Denton told mental_floss in an email. But he does suspect that the single-sex lifestyle has something to do with it.

"We do have other physiological data (locomotor endurance on treadmills) that suggests that unisexuals are different as a group when compared to multiple sexual species, which might suggest that the regeneration difference here is due more to polyploidy than genome composition," Denton said. "Overall, there is a great deal of work to be done disentangling the strange genomic makeup of these animals."