Marbled Crayfish

The marbled crayfish, also known by the German aquarium trade name Marmorkrebs, is unique among decapod crustaceans for reproducing entirely without males, with every individual a genetically identical clone of its mother. The species is believed to have arisen from a single genetic mutation in a wild slough crayfish lineage sometime in the twentieth century, first appearing in the German pet trade during the 1990s. Because a single individual can found an entire population on its own, aquarium releases have allowed it to establish wild breeding populations far outside any natural range, including waters in Germany, Madagascar, and elsewhere. Its rapid, unchecked reproduction and lack of any need for a mate have made it a serious invasive concern in the freshwater systems it has reached, particularly in Madagascar where it competes with native crayfish and disturbs rice paddy ecosystems. It closely resembles its sexually reproducing relatives in body form, being an ordinary sized freshwater crayfish with a mottled, marbled shell pattern. Its existence is studied by biologists as a rare real world example of a new, fully asexual animal lineage emerging within recent memory.