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by David Catchpoole Since its discovery in Germany in 1995, the marbled crayfish has spectacularly spread across Europe and parts of Africa in huge numbers. Because it reproduces asexually (i.e. only a female is needed), this ‘self-cloning’ crayfish can establish a population in a lake or waterway starting with just one individual. Bearing a large number of young, the marbled crayfish appears to be out-competing ‘native’ crayfish, and some authorities have officially declared it a pest. Recent genetic analysis has found that the marbled crayfish has three sets of 92 chromosomes rather than the usual two. With two of these sets being identical to each other and only slightly different from the third set, researchers surmise that the marbled crayfish arose from a mating between two slough crayfish, Procambarus fallax. They say that one of those parents must have had an abnormal egg or sperm with two copies of its chromosomes rather than the usual single set., And so the marbled crayfish now can copy itself as many other asexually-reproducing organisms do via apomictic parthenogenesis. Its eggs do not need to be fertilized by sperm, and all contain the same three sets of chromosomes. Genetic analysis of marbled crayfish from various locations …
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