Before about 25 years ago, the species simply did not exist. A single drastic mutation in a single crayfish produced the marbled crayfish in an instant. [...] "We may never have caught the genome of a species so soon after it became a species," said Zen Faulkes, a biologist at the University of Texas Rio Grande Valley, who was not involved in the new study. [...]
As marmorkrebs became more popular, owners grew increasingly puzzled. The crayfish seemed to be laying eggs without mating. The progeny were all female, and each one grew up ready to reproduce. [...] "People would start out with a single animal, and a year later they would have a couple hundred," said Dr. Lyko. [...]
The scientists concluded that the new species got its start when two slough crayfish mated. One of them had a mutation in a sex cell -- whether it was an egg or sperm, the scientists can't tell.
Normal sex cells contain a single copy of each chromosome. But the mutant crayfish sex cell had two. Somehow the two sex cells fused and produced a female crayfish embryo with three copies of each chromosome instead of the normal two. Somehow, too, the new crayfish didn't suffer any deformities as a result of all that extra DNA.
It grew and thrived. But instead of reproducing sexually, the first marbled crayfish was able to induce her own eggs to start dividing into embryos. The offspring, all females, inherited identical copies of her three sets of chromosomes. They were clones.
Now that their chromosomes were mismatched with those of slough crayfish, they could no longer produce viable offspring. Male slough crayfish will readily mate with the marbled crayfish, but they never father any of the offspring. [...]
Thanks to the young age of the species, marbled crayfish could shed light on one of the big mysteries about the animal kingdom: why so many animals have sex. Only about 1 in 10,000 species comprise cloning females. Many studies suggest that sex-free species are rare because they don't last long. [...]
There are a lot of clear advantages to being a clone. Marbled crayfish produce nothing but fertile offspring, allowing their populations to explode. "Asexuality is a fantastic short-term strategy," said Dr. Tucker.
"Asexuality is a fantastic short-term strategy."