Ruminations

"The whole species is essentially female," Mutant Clones : Procambarus virginalis

"It's extremely impressive. Three of us once caught 150 animals [marbled crayfish] within one hour, just with our hands."
"People would start out with a single animal, and a year later they would have a couple hundred."
"Maybe [as a singular species] they just survive for 100,000 years. That would be a long time for me personally, but in evolution it would just be a blip on the radar."
Frank Lyko, biologist, German Cancer Research Center

"If you have one animal, essentially, three months later, you will have 200 or 300. The whole species is essentially female."
"In 2017, they occupy the area [in Madagascar] the size of Ohio. That's a hundred-fold increase in just a decade."
Wolfgang Stein, neurophysiologist, Illinois State University

"Based on what is known about the reproductive behaviour of the marbled crayfish, we do not recommend Canadians keep these animals as pets."
"Human release of animals is one of the ways invasive species are introduced and become established in new areas."
"Unauthorized release of any aquatic animal into a waterbody from which they did not originate is illegal under the regulations."
Becky Cudmore, regional manager, aquatic invasion species program, Fisheries and Oceans Canada

The all-female marbled crayfish reproduces by cloning — and while it's a relatively new species, there are already huge populations around the world. (Submitted by Wolfgang Stein)

Crayfish enthusiasts have the option of going along to their favourite pet store to poke about in the aquariums there and pick up a new pet for themselves, a marbled crayfish. In the late 1990s the marbled crayfish attracted the attention of aquarium hobbyists in Germany. Professor Lyko tracked down one individual who bought what the shop owner described to him as a "Texas crayfish", back in 1995. The size of the beast amazed the hobbyist, but nowhere near as much as the enormous batches of eggs it produced.

Hobbyists eventually realized that their female crayfish hadn't come in contact with a male of the species, yet was producing hundreds of eggs at a time. The person whom Dr. Lyko interviewed described his desperate efforts to give away resulting crayfish to friends. They were called marmorkrebs and were available in pet shops throughout Germany. With their popularity, owners realized these crayfish never stopped laying eggs yet had no mates, all their progeny were female and each capable of reproducing.

It was a short distance from acquiring these unique little beasts, observing their reproduction, running out of friends to gift them with, and taking them finally in desperation to local streams, rivers, lakes where they effortlessly and studiously multiplied. And it is these crayfish that Dr. Lyko and his research crew have studied in the past five years, managing to sequence the genomes. The study published recently in the scientific journal Nature, Ecology and Evolution, pointed out that the marble crayfish, now commonly seen around the world, is one of nature's most remarkable species.

A scientific marvel, in the sense that twenty-five years ago they didn't exist. Their amazing proliferation represents one of nature's true anomalies. In that a sole drastic mutation in one lone crayfish produced, in an instant of time, the marbled crayfish as it is known today. The mutation is credited with the capability of the creature to clone itself, and in that quarter-century of existence it has spread through Europe and has entered other continents to spread there as well. Its presence in Madagscar threatens native crayfish; it arrived in 2007 and now numbers in the millions.

"We may never have caught the genome of a species so soon after it became a species", marvelled biologist Zen Faulkes, of the University of Texas Rio Grande Valley, commenting on the study. Scientists, in 2003, confirmed the marbled crayfish absolutely were producing selfclones. Small portions of DNA were sequenced from the animals and a similarity found to a crayfish species called Procambarus, native to Central and North America. It took another ten years and Dr. Lyko and colleagues determined the entire genome of the marbled crayfish.

The Marmorkrebs thrived wherever they landed; initially taken by hobbyists out of their crowded aquariums to local waterways. The crayfish, it would appear, took themselves out of the lakes and streams they began to populate, and walked themselves over to uninhabited waterways to begin colonizing them as well. Marbled crayfish colonies turned up in the Czech Republic, Hungary, Croatia and Ukraine in Europe, and soon enough in Madagascar and Japan. They are now, as well, in North America.

Scientists hypothesize that two slough crayfish likely mated, one of which had a sex cell mutation. The mutant crayfish sex cell had two copies of each chromosome, where normal sex cells contain only one. The two sex cells managed to fuse and the result was the capacity to produce a female crayfish embryo with three copies of each chromosome rather than the normal two.

What is also notable is that no deformities resulted out of that extra DNA. The new mutant crayfish had no need of normal sexual reproduction since she was able to induce her own eggs to divide into embryos, all of which resulted in females inheriting the identical copies of her three sets of chromosomes and themselves capable of multiplying. The rest is scientific history.