The Marbled Crayfish: Attack of the Crustacean Clones

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It looks innocent enough, a small marbled crayfish that resembles a tiny lobster. Across its entire body, pleasing patterns catch the eye. Perhaps, one might like to keep it as a pet? Unfortunately, that’s what a German aquarist thought when they purchased a large specimen labeled as a “Texas crayfish” around 1995. 

By 2003, scientists determined the crayfish’s offspring were all female clones. 

Since then, the freshwater crustacean spread like cancer across much of the world. From Germany, they spread throughout Europe, Africa, and as far as Japan.

A new species arose and is threatening to invade the globe.

The Marmorkrebs ‘Murican Mutant

Today, the marbled crayfish or “Marmorkrebs” is banned in the European Union and threatens ecosystems across the planet. 

Like one in 10,000 species, the marbled crayfish is all-female, spreading asexually from clones. However, it’s the only decapod crustacean with the ability.

Recently, we discussed the almost all-female Mourning Gecko, a reptile that similarly reproduces through parthenogenesis. For these species, no males are required for reproduction.

When a marbled crayfish mutant was born in Germany, the Attack of the Crustacean Clones began. Interestingly, each marbled crayfish shares an identical genome.

A map by biologist Zen Faulkes shows where the crayfish are found today:

Mutant Offspring

Scientists studying the marbled crayfish’ genome believe that the mutant species probably resulted from two slough crayfish. The German aquarist obtained the imported crayfish from a 1995 insect fair. Someone may have collected them from the Florida Everglades. 

Then, they mated and produced the first marbled crayfish, now called Procambarus virginalis. 

“That one animal founded the whole species, and now we have billions worldwide,” says Wolfgang Stein, a neuroscientist at Illinois State University. 

Slough Crayfish
Image: Procambarus fallax by Alexander Mrkvicka via Wikimedia Commons (CC BY-SA 3.0)

Notably, slough crayfish are known as Procambarus fallax, which is found in the Satilla River in Florida and Georgia. Thus, the crayfish created an entirely new mutant species! 

A Little Extra

Scientists speculate that the parents may have come from different regions after inspecting the crayfish’s chromosomes. One parent crayfish probably had an “abnormal egg or sperm” with two copies of its chromosomes, enhancing the offspring’s genetic variation.

Each marbled crayfish has three copies of each chromosome instead of the usual two sets. (one from each parent) 

In the wild, such a pairing would have been unlikely. If you have ever tried to keep an aquarium, you know that producing offspring in aquariums also presents challenges.

“It is interesting to contemplate the global, ecological implications of an exceedingly rare evolutionary event arising in someone’s aquarium,” Susan Adams, an aquatic ecologist, told Science.

What would happen if the marbled crayfish found its way back to its parents’ homeland? So far, it’s been banned in some states like Michigan, for its risk to native wildlife.

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Adaptable and Prolific Clones

When the anonymous German aquarist saw how prolific his specimen was, he started taking them to the local pet store. Soon, they wound up in other aquarists’ homes, where they rapidly reproduced with hundreds of eggs.

Sometimes, people would release them into lakes. (As always, releasing pets into the wild is a horrible plan, as we’ve seen with the Argentine Tegus in the southern states.)

Occasionally, marbled crayfish leave the water and walk on land to find a new home. Since only one specimen can reproduce, entire populations can spring up wherever they roam.

Since they will eat almost anything, from rotten leaves to small fish, they find what they need in most freshwater environments. Unfortunately, they also rapidly outnumber native species.

Mutant Powers

Worse, marbled crayfish are exceptionally hardy, able to tolerate temperature swings and water conditions. In fact, they will even live in water with varying salinity and acidity as well as polluted water.

Although clones tend to lack genetic diversity, this mutant is highly adaptable. Why? Scientists believe the crayfish’s extra chromosomes may offset the usual disadvantages. 

However, since all of the crayfish are identical, they are also equally vulnerable should a disease arise that threatens them. That’s partly why sex-free species are rare as a pathogen can wipe them all out. Without genetic variation, no individuals may have the ability to resist infection.

In most cases, merely having extra chromosomes would be fatal. However, not in this unique, incredible case.

See more from SciShow:

Intentional Release?

Since marbled crayfish are so prolific, it makes sense some people think they are a perfect item to raise for food. That’s why farmers in Madagascar intentionally imported and released them into the wild around 2007. After all, they are delicious and cheap, offering an easy way of life, or so they thought.

Unfortunately, as we’ve seen, these crustaceans spread like wildfire and are harmful to native species. Today, the seven native crayfish species in Madagascar are threatened as the clones have multiplied by the millions. Walking across the rice paddies in Madagascar, they have taken over and will remain a nuisance.

Today, some pet stores still sell these animals as they remain legal in some states. Often, people may be unaware of how invasive they can be. Our best recommendation is to avoid them like the plague and inform the pet stores why you are doing so.

Cancer Research

If the marbled crayfish is useful at all, it may be in understanding similar phenomena: cancer. Frank Lyko, a biologist at the German Cancer Research Center, studies them.

By studying their unique genetic makeup, researchers hope to understand how tumors grow. Similar to the crayfish, tumors clone themselves and adapt to diverse environments.

“What we see in slow motion with the marbled crayfish evolution is something that happens during the very early stages of tumor formation,” Lyko says.

Hopefully, what Lyko and other researchers find will lead to knowledge of how tumors evolve in the early stages. In the meantime, the attack of the clones continues.

Perhaps, marbled crayfish will continue to spread for up to 100,000 years, suggests Lyko. So, he’s saying their days may be numbered, after all? 

Related: A Practically Immortal Animal Is Spreading Across the Planet

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Featured image: Marmorkrebs Procambarus fallax forma virginalis by Chucholl C. via Wikimedia Commons (CC BY-SA 3.0)