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Crayfish Clone Invasion

Researchers first became aware of the marbled crayfish when a German aquarium owner contacted them in 1995 after a bag of "Texas crayfish" took over his aquarium, the Atlantic reports. The crayfish, dubbed Marmorkreb in German, turned out to be parthenogenetic clones of one another and have since been found in the wild in Germany, Italy, Slovakia, Sweden, Japan, and Madagascar, it adds.

Researchers led by the German Cancer Research Center's Frank Lyko sequenced the marbled crayfish. As they report in Nature Ecology and Evolution, the marbled crayfish is triploid with a 3.5-gigabase-pair genome harboring more than 21,000 genes. 

They also found that it is closely related to the slough crayfish, Procambarus fallax, the New York Times notes. Lyko and his colleagues suspect that the marbled crayfish came about when two slough crayfish mated, but one of them had a sex cell with two complements of chromosomes, rather than one, the Times adds. The resulting female crayfish could then reproduce parthenogenetically and spread rapidly.

The Atlantic notes that when the researchers compared the genomes of 11 marbled crayfish from spots from all over the world they found that the crayfish had few genetic differences between them all. This, the researchers say in their paper, "support[s] the notion that the global marbled crayfish population represents a single clone."