Some Salamanders Will Travel Incredible Distances to Mate


Some salamanders, like this Ambystoma texanum, will do anything for love  including walk a really, really long way. Greg Schecter/Flickr
Some salamanders, like this Ambystoma texanum, will do anything for love including walk a really, really long way. Greg Schecter/Flickr

Just as some humans are willing to travel a really, really long way for a some sweet loving, long-distance daliances aren't unheard of in the animal world.

Take the smallmouth mole salamander (Ambystoma texanum), normally a mild-mannered, stumpy-legged little amphibian from the Midwestern United States. A new study published in the journal Functional Ecology finds that this salamander will travel an average of six miles (10 km), and up to nine miles (15 km) to reach new breeding ground, crossing all sorts of treacherous terrain in order to find a mate they're almost definitely not related to. That's pretty impressive, especially when you consider that the largest these salamanders grow to be is about 7 inches (18 centimeters) long.

Because salamanders are basically the walking Chicken McNuggets of the forest, most spend a significant portion of their lives hiding under logs. In fact, it's tremendously difficult to study them because, aside from their secretive habits, you can't fit them with tracking devices — their skin is too delicate for that. But when it's time to mate, the salamanders come out of hiding prepared to toddle tirelessly for miles in order to find some action in a foreign land.

But let's be clear: not all salamanders mate. It's true! The research team studied two species of Ohio mole salamanders from the genus Ambystoma — one that reproduces sexually, and another that's all-female whose members reproduce by cloning themselves or fertilizing their eggs with spare bits of sperm they find lying around on the forest floor. They found that the sexually reproducing species had considerably more stamina for walking on a tiny treadmill than their unisexual counterparts.

"They're like endurance athletes," said study author Robert Denton, a Ph.D. student in the Department of Evolution, Ecology and Organismal Biology at Ohio State. "Some of them could walk for two-plus hours straight without tiring themselves. That's like a person lightly jogging for 75 miles before wearing out."

The researchers figured out some of the sex-having salamanders were embarking on these Tolkien-esque journeys by taking genetic material from 445 salamanders from wetlands all over Ohio and cross-referencing that data with information about who was most closely related to whom. Most individuals had genes that matched up with the wetland they lived in, but some seemed to have come from populations miles away. To assess whether multi-mile odysseys would even be possible for the animals, put individual salamanders on a treadmill in a lab and observed their walking capabilities. It turned out the sexually reproducing salamanders could walk up to four times farther than the all-female species without getting fatigued.

"Maybe the best explanation for why sexual salamanders travel so far is because they have to: On a large landscape with few places to breed, the animals that can cross that distance are the ones that survive and reproduce," says Denton. "Perhaps the more interesting question is why the all-female salamanders don't go very far, and we think that has to do with the physiological costs of not having sex. Essentially, not mixing up your genomic material often enough likely causes some problems for genes that you need to make energy."