A crayfish species discovered in the fish tanks of German aquarists is the first of its kind to reproduce asexually. Following up on rumors among those who keep fish in home aquariums, biologists have confirmed that the mysterious crayfish clones itself to reproduce. The finding suggests that the animal could crowd out natural crayfish species should it escape into the wild.
It's not clear exactly where the crayfish comes from, but was first noticed in the fish tanks of hobbyists in the 1990s. Aquarists were baffled when they noticed that even single crayfish could reproduce: None of the 10,000 species of decapods--a group that includes shrimp, lobster, and crayfish--are known to reproduce without using sperm to fertilize an egg.
To solve the mystery, zoologist Gerhard Scholtz and his team at the Humboldt University in Berlin kept a single female in a laboratory tank. Although the female harbored no male spermatophores from previous copulations, she laid eggs. Still, there are other modes of reproduction--the crayfish might have both male and female reproductive organs. So Scholtz's team collaborated with biologists at the University of Heidelberg, examining the reproductive system of their laboratory crayfish populations. They found only ovaries. The fact that the animals produced only female offspring helped confirm their theory that the eggs alone could mature into full-blown crayfish, a rare trick known as parthenogenesis.
Concerned that a parthenogenic crayfish might invade native ecosystems, Scholtz's team conducted genetic tests and compared the strain, which they called Marmorkrebs, with other species. Worryingly, they report in the 20 February issue of Nature, Marmokrebs is closely related to a North American species; American crayfish carry a fungal disease known as infectious crayfish plague, which in the past has wiped out wild populations of crayfish across Europe. Scholtz warns that the release of just one Marmokrebs into a European ecosystem could be a disaster for native crayfish, both because of the disease and its asexual reproductive abilities.
The discovery surprised Keith Crandall, a crayfish specialist at Brigham Young University in Provo, Utah. He agrees that releasing the crayfish into the wild could indeed endanger populations of European natives. Scientifically, he wonders whether the parthenogenetic crayfish is some kind of "aquarium beast" that evolved in captivity, or whether there are natural populations that reproduce this way.