Scientists Discover Worm That Has Three Sexes

One of the sexes can self-fertilize and they are sexually fluid.

A photo of small earthworms in the ground
Maksimilian / Shutterstock

One of the sexes can self-fertilize and they are sexually fluid.

Scientists have found a species of worm that has three sexes. The worm produces males, females, and hermaphrodites, which is a biological term for an organism with reproductive organs from both sexes. According to Phys.org, the name of the species is Auanema rhodensis and researchers say that it’s breaking the rules when it comes to genetics.

Hermaphroditism isn’t that unusual among invertebrates, but this worm’s version of it is unique. That’s because the hermaphrodites of the species can self-fertilize, which means that one worm can impregnate itself.

“What’s not quite so common are self-fertile hermaphrodites. Think about earthworms: They’re hermaphrodites, but it still takes two, because of the way the sex works, they’re not self-fertile,” said Diana Shakes, a professor who has been studying the worms.

There are other types of hermaphroditism that have previously been observed, she said. For example, male oysters and other species of shellfish change from male to female as they age.

But the Auanema rhodensis is different and it’s groundbreaking. Their bodies have the exterior characteristics of a female but they generate both sperm and eggs.

What’s more, the worms are a trisexual species. The hermaphrodite worms may be self-fertilizing but they are also willing to reproduce with both males and females. They are sexually fluid.

But as Phys.org notes, their self-fertilization abilities definitely present some evolutionary advantages. They don’t have to be concerned about selecting a mate. That’s unnecessary for reproduction. The hermaphrodites can easily produce genetic copies of itself. According to Shakes, they also have a toughness that the males and females don’t have and they have the ability to survive difficult living conditions. But there’s also a big drawback to it since the offspring don’t get the genetic diversity that male/female couplings create. This typically endows the children of these unions with certain biological advantages.

According to the Daily Mail, the worm is pretty rare and has been found in Connecticut and the Appalachian region in Virginia. They are extremely small, measuring about a millimeter long. Scientists are still unclear about a lot of their behavior when they’re not in a lab. But the professor says that, in their natural habitat, there are lots of the hermaphrodite version of the worm.

The full text of the research can be found in a paper authored by Shakes in the journal Current Biology.