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It sounds like something out of a sci-fi movie: a new crayfish population made entirely of asexually reproducing, all-female clones. But is it a new species?

Hosted by: Hank Green

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Imagine waking up one morning to find that your pet crayfish had multiplied like an invasion of ten-legged aquatic Tribbles, even though it was the only animal in the tank and had been for quite some time. It sounds impossible, something out of a sci-fi movie...

What is this hypothetical you're presenting to us Hank Green? I'm presenting to you the exact story a German aquarium owner told scientists in 1995. And in 2003, a paper in the journal Nature confirmed it:.

This new crayfish population was made entirely of asexually reproducing, all-female clones. Now, they’re taking over. Plot Twist!

Many researchers think this crayfish should be considered a new species, and they’ve dubbed it Procambarus virginalis.​ But it’s more commonly called the ​. Marmorkrebs​ or ​marbled crayfish​. Instead of being produced in some top-secret, diabolical clone lab, it probably arose thanks to a simple mutation.

Normally, crayfish have two sets of chromosomes that carry their genetic information -- one inherited from each parent. But some time in the 1990s, a single crayfish was born with three sets -- one from one parent, and two from the other. Scientists think the parents were a different type of crayfish native to the Florida Everglades, and that one of them passed along the extra chromosomes through a mutated sex cell.

Having entire extra sets of chromosomes is typically fatal in animals, but for some reason, this baby was a healthy female... It was just… different. Specifically, it didn’t need to partner to mate.

Unlike all other kinds of crayfish, it could reproduce asexually through a process called parthenogenesis​, laying hundreds of eggs that were exact genetic copies of itself. Then, each of those eggs grew up to be another self-cloning female that started taking over, Tribble-style. If you haven't seen the trouble with tribbles the Star Trek original series show that's because you're not old like me.

If the new species had stayed confined to aquariums, the marbled crayfish would have been nothing more than a genetic researcher’s oddity and an aquarium hobbyist’s nightmare. Unfortunately, though, the rapidly-multiplying clones made it into the wild - likely on a bunch of separate occasions -- where they now live and copy themselves over and over and over. Because only one individual is needed to start a new population and every individual is fertile, marbled crayfish can rapidly overrun new environments and leave native species in the dust.

Since its discovery, this crayfish has spread through Europe and Africa and has even appeared as far away as Japan. To prevent them from invading even more areas, the European Union and some U. S. states have banned them from being sold, but we probably won’t see them disappear any time soon.

Besides their uncanny ability to multiply, some people still intentionally release marbled crayfish -- like some farmers in Madagascar, who raise them for food. And in some places, it’s still possible for aquarium hobbyists to buy them. Getting rid of invasive species is a huge undertaking, especially when every single individual can restart the population.

So if you find yourself admiring a marbled crayfish at your local aquarium supply shop, consider what you’ll do to responsibly care for your future clone army. And then kill it! Right there in the sto...don't do that.

Thanks for watching this episode of SciShow! If the idea of invasive species gets you all riled up in the morning, you might also enjoy our episode about why we can’t just kill them all off. [♪OUTRO].