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Marbled Crayfish That Can Clone Themselves Originated From One Mutant Ancestor

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A crayfish with remarkable ability to clone itself is taking over Europe. Interestingly, the species did not even exist about 25 years ago.

Marbled Crayfish

The creature started to become popular among aquarium hobbyists in Germany in the late 1990s. The creature can lay enormous numbers of eggs at a time. Soon, marmorkrebs started to show up in pet stores in Germany.

Owners eventually noticed that that they were laying eggs without mating. By 2003, scientists were able to confirm that the marmorkrebs were indeed producing clones of themselves.

"It has been rumoured that an unidentified decapod crustacean, a crayfish of marbled appearance and of uncertain geographical origin that was introduced into the German aquarium trade in the mid-1990s, is capable of unisexual reproduction (parthenogenesis)," researchers wrote in Nature.

"Here we confirm that this marbled crayfish ('Marmorkrebs') is parthenogenetic under laboratory conditions and use morphological and molecular analysis to show that it belongs to the American Cambaridae family."

Where did this creature come from, and why do they reproduce in large numbers?

Descended From A Single Mutant Crayfish

In a new study, German Cancer Research Center biologist Frank Lyko and colleagues sequenced the genomes of several crayfish specimens to trace the origins of the marbled creature.

It appears to have evolved from a species called the slough crayfish. The new species was likely born from the mating of two slough crayfish, one of which had a mutation in the sex cell.

Sex cells normally contain only one copy of each chromosome, but this mutant crayfish had two. The two sex cells apparently fused and produced a female crayfish embryo that had three copies of each chromosome.

The new crayfish did not suffer from deformities regardless of its extra DNA, but instead of reproducing sexually like its ascendants, it can induce its own eggs to divide into embryos, producing an all-female offspring.

These offspring contain the same copies of their mother's three sets of chromosomes, which essentially makes them her clones. These clones also produce fertile offspring, which allows the population of the new species to explode.

"Our results show that the marbled crayfish genome consists of two almost identical copies of one genotype and a third copy of a comparably divergent, but still homologous genotype," researchers wrote in their study.

"These findings are consistent with the model that the marbled crayfish genome originated from an autopolyploid P. fallax gamete and the mating of two distantly related P. fallax individuals."

Exploding Populations

Over the next two decades after it was first introduced in Germany, the creatures established populations in the wild and grew in numbers. They also started to invade new lakes and streams and now have populations in Hungary, Czech Republic, Croatia, and Ukraine in Europe, and even in Japan and Madagascar.

The European Union has already banned the production, distribution, and release of the species in the wild.

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