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Growing Population of Crayfish Has One Female Ancestor

The new species reproduces by cloning itself and is entirely female.

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A genome study has proven that all specimen of marbled crayfish originate from a single female. About 30 years ago, the original clone evolved in an aquarium.

It all began with one female.

A slough crayfish was fished from the Everglades in the U.S. and taken to an insect fair in 1995 where a hobbyist bought it. Then, for reasons unknown, that slough crayfish became a new species called a marbled crayfish (Procambarus virginalis) after it began reproducing asexually, essentially cloning itself.

Unable to care for the rapidly increasing offspring, the original owner took them to pet shops where other hobby aquarium keepers bought them. Since then, the world has been invaded by that one crayfish's daughters. "That one animal founded the whole species, and now we have billions worldwide," says Wolfgang Stein, a neuroscientist at Illinois State University. He and a team of researchers recently sequenced the genome of this new, marbled species and published their find in the journal Nature Ecology and Evolution.

It added to a study published in 2003 that found the species essentially reproduced through cloning, a process called parthenogenesis.

After sequencing the genome of about a dozen marbled crayfish, scientists were able to work backwards to find the original female, says study author Frank Lyko, a researcher from the German Cancer Research Center.

"The scale of this [family] tree is extremely small," he says. In fact, they found only a few hundred variants in the crayfish's large genome.

"If we had more than one animal as a founder, we would have greater genetic differences," Lyko adds .

Researchers were also surprised to find that marbled crayfish had three sets of chromosomes. Most animals have only two sets: one from each parent.

Lyko says this likely influences how genes are expressed in each new marbled crayfish. Not only would this provide a buffer from inheriting a genetic mutation, but it may also help the species adapt to a host of different environments.

Marbled crayfish are currently found throughout Europe and Madagascar. Stein says in just a decade's time, they've been able to grow from occupying a space the size of Rhode Island to occupying a space the size of Ohio.

Not only that, they also exist throughout the country's varied ecological regions. On his website, biologist Zen Faulkes from the University of Texas Rio Grande Valley keeps an updated map of where marbled crayfish can be found. They're considered an invasive species that aggressively outcompetes comparable marine organisms.

"You find it in acid water and in basic water; polluted water and clean water; it's always the same genetic makeup," adds Stein.

Lyko says this crayfish has been able to adapt to such diverse environments because of the way it expresses those diverse genes.

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"In one environment, copy a is expressed, and in another environment, copy b is expressed," he says.

Studying the unique genetic makeup of marbled crayfish is informing what researchers now about tumors, which also evolve by cloning and are capable of adapting to diverse environments.

"What we see in slow motion with the marbled crayfish evolution is something that happens during the very early stages of tumor formation," Lyko says.

He adds that their research is foundational, so they aren't developing treatments based off their crayfish studies, but he's confident the small, invasive crayfish could help them build a model for understanding the early stages of tumor evolution.