The genome sequence of the marbled crayfish is reported in a paper published online this week in Nature Ecology & Evolution. The genome helps explain how this asexual crustacean has gone from a new species that arose from the German pet trade just two decades ago to a potent invasive species in Madagascar.
The marbled crayfish (Procambarus virginalis, also known as Marmorkrebs) was first identified in the 1990s, and is thought to have arisen when individuals of the related North American species Procambarus fallax, kept as aquarium pets in Germany, acquired a third full set of chromosomes, unlike most sexual animals which have two sets of chromosomes, one from each parent. Since then, marbled crayfish have spread from captivity to freshwater ecosystems around the world, and seem particularly well adapted to Madagascar.
Frank Lyko and colleagues sequenced the genome of 11 individual marbled crayfish originating from both the wild and the pet trade, as well as individuals of P. fallax and another related species. The authors confirm that all the marbled crayfish individuals are almost genetically identical, with just a few changes since the species arose. They also found that one set of chromosomes is quite distinct from the other two, suggesting the species descended from two distantly related P. fallax individuals. Using individuals caught in the wild in Madagascar, the authors show that the population there has expanded 100-fold in geographic area in the last ten years and they estimate it consists of millions of animals.
These results provide the first sequenced genome of a decapod crustacean, a group that includes crabs, lobsters, prawns and shrimps. The study also offers clues about how a new species can arise rapidly and, because of genetic variation within each individual, how it can survive despite all individuals being almost genetically identical. In addition, the study highlights the rapid spread of this invasive species in Madagascar with the potential to harm native species and freshwater ecosystems.