By Ewen Callaway
Molecular biologists have sequenced the genome of an invasive species of crayfish that can reproduce without mating and is spreading rapidly across Madagascar. The marbled crayfish (Procambarus virginalis) was first spotted in aquariums in Germany in the 1990s. Now, DNA sequencing suggests that the species is probably the product of two distantly related members of a different crayfish species, a team reported on 5 February in Nature Ecology and Evolution1.
The marbled crayfish has already been banned in the European Union and some parts of the United States because of the threat it poses to freshwater ecosystems. The species has now spread into the interior of Madagascar and risks crowding out seven native crayfish species. “This is a very aggressive population,” says Frank Lyko, a molecular biologist at the German Cancer Research Center in Heidelberg, who co-led the study. “If the marble crayfish continues to explode at its current pace, it will probably outcompete endemic species.”
The marbled crayfish carries three copies of each chromosome, instead of the usual two2. Lyko and his team sequenced the genome of a single individual from a laboratory strain known as Petshop. Its DNA revealed a surprise: it had two different genotypes at many places of its genome. The best explanation for this pattern, says Lyko, is that two of the chromosomes are nearly identical in sequence, but the third differs substantially.
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