Attack of the Clones: Creature That Started as Pet Now Multiplying Out of Control

The marbled crayfish evolved into a new species out of the pet trade. Sina Tönges

Most species of crayfish reproduce the same way that humans do: by having sex. But one species of crayfish that evolved out of the pet trade can do something unique—clone itself—and this ability has led populations of the crustacean to spawn out of control.

For a study published today in the journal Nature Ecology and Evolution, researchers sequenced the genomes of 11 marbled crayfish, both from the wild and from the pet trade. They found that the genomes in all 11 animals were nearly identical, meaning that they don't reproduce sexually, and that they are officially a different species than their North American mother species, Procambarus fallax.

"Here we have an evolutionary event that has happened only a very short time ago," Frank Lyko, head of divisions of epigenetics at the German Cancer Research Center, told Newsweek. "Certainly there will be some changes, genetic changes over time, that will make it more normal. At this specific time point in evolution it's very unique."

Lyko explained that forming a new species usually takes evolution thousands of years or more. However, it was only a few decades ago that the North American species of crayfish entered the pet trade, and now a different, exceptional species has emerged from them.

The way that this new species formed is exceptional as well. P. fallax came to Germany as a pet, sold over the internet and in pet and aquarium stores. But some time between 1990 and 1995, the animals evolved into a new species. The new species had marbled coloring, and people first noticed that it was different from the original species because there was only one sex.

"People wondered, 'it's only females, where are the males?'" Lyko said.

It turns out that marbled crayfish only exist in female form, spawning clones of themselves two or three times a year in a process called parthenogenesis.

The marbled crayfish can start with one and then clone itself into millions. Ranja Andriantsoa

Because they spawn so quickly and easily, they're easy to breed (clone) in captivity. That made them ideal for people selling the animals as pets, but it became a problem for people who only want one in their aquarium.

"You put them into your aquarium and a year later you have hundreds of them," Lyko explained. No dad required.

Then what are you going to do? You can kill the others, sell them, or release them into nearby waterways. If the animals were once your pets, you might be inclined to release the extras—which, in turn, can create thousands more rapidly.

That's how the species became invasive to Germany and Madagascar where they were also popular pets. The scientists concluded that there are now millions of this unique but unstoppable creature crawling throughout Madagascar and constantly multiplying.