Cloning In Nature: All Marbled Crayfish Clones Of One Individual Female

Parthenogenesis, Greek for a virgin birth (literally “virgin creation,” not applicable to religious figures like Jesus of Nazareth), has been around among different species in nature for over hundreds of thousands of years, and has long been known about in science. Since the process involves no contribution of genetic material from a male parent, the offspring are genetic clones of the mother.

These natural clones are not a rarity in themselves, but when it comes to an entire species having the exact same genetic code, it is noteworthy. And that is the exact case when it comes to marbled crayfish (Procambarus virginalis), a species where every single individual is a natural clone of the same parent female.

The lone and unambiguous progenitor of the entire species, which is also called Marmorkrebs, was born about 30 years ago in an aquarium in Germany, itself perhaps an offspring of two slough crayfish that had been imported from Florida. No natural populations of marbled crayfish are known prior to its discovery in the pet trade in Germany.

That individual caught scientists’ attention because it was reproducing by itself in an aquarium. And new research using genome sequencing and comparison of individual specimens — all of them females — has proven they are all clones of the first one. Despite that, the species has established itself in a large number of places around the Earth, adapting to a variety of habitats.

“We could detect only a few hundred variants in a genome that is larger than the human genome. That is an incredibly small number,” Frank Lyko from the German Cancer Research Center (Deutsches Krebsforschungszentrum, or DKFZ) in Heidelberg, who coauthored the study, explained in a statement Tuesday. “Epigenetic variants are often influenced by genetic variants. In Marmorkrebs, however, epigenetic variation is independent, because there is virtually no genetic variation,” he added, to explain how the high adaptability displayed by the species.

The DKFZ researchers got interested in studying P. virginalis because of these epigenetic mechanisms, which control the interpretation of genetic information. These mechanisms are also a factor that influence the risk of cancer and growth of the disease. Another similarity between the crayfish and cancerous tumors is they both go through a phenomenon called clonal evolution.

“Marmorkrebs is an animal that reproduces clonally and therefore represents a model of a central aspect in tumor development. Tumor genomes also evolve clonally, because they go back to a single original cell,” Lyko said.

The adaptability of the marbled crayfish has made it a pest species in many places (for a species that evolved in an aquarium, it would likely be a pest wherever it went), and it has already spread from Germany to as far as Sweden, Japan and Madagascar. In Madagascar, it threatens the existence of seven native crayfish species.

The open-access study, titled “Clonal genome evolution and rapid invasive spread of the marbled crayfish,” appeared Monday in the journal Nature Ecology & Evolution. Other than DKFZ, researchers from Université d’Antananarivo, Madagascar, and Illinois State University, Normal, were also coauthors on the report.