The fish has been replicating for 100,000 years, including all females

Here Molly Amazon (Poecilia formosa) includes all children. For the past 100,000 years, they have been mating with male molly fish of other species to trigger the process of self-cloning, or female parthenogenesis (gynogenesis), but the young do not carry the DNA of those males.

The fact that the Amazon molly fish can survive for such a long time has long been a mystery to the scientific community. According to Edward Ricemeyer, a computational biologist at Ludwig Maximilian University Munich, models of how genetic mutations accumulate in asexual reproduction suggest that the Amazon molly fish “should have gone extinct in about 10,000 years.” Experts wonder how they do not accumulate harmful mutations when natural selection does not continuously eliminate these mutations.

To find out, Ricemeyer and his colleagues examined the genes of some Amazon molly fish and discovered that they had been “cleaning up” their genes for a long time. New research published in the journal Nature.

Molly Amazon is a small, round-finned fish, no larger than a thumb. Named after the female warrior clan in Greek mythology, this fish appeared as an Atlantic molly fish (Mexican poetry) female pairs with sailfin molly (Poecilia latipinna) male. The mating process between individuals of different species usually creates sterile offspring, but in this case it creates a new species capable of giving birth to copies similar to the original.

Genetic analysis shows that harmful mutations appear in Amazon molly fish with the same frequency as their sexually reproducing relatives. However, the animal appears to utilize a little-known genetic process that ensures those mutations are eliminated or corrected.

This process, called transgenesis, works by replacing a segment of chromosomal DNA with a corresponding segment copied from an identical sequence on another chromosome. Mammals, including humans, also have this ability, primarily to repair DNA damage.

But with the Amazon molly, gene transfer appears to play a similar role to cross-recombination – the process of mixing genes from one parent in sexually reproducing species. Like cross-over recombination, transgenesis creates genetic diversity in Amazon molly fish for natural selection to act on, thereby eliminating and correcting unwanted mutations.

Scientists once suspected asexual species had this solution, but according to Ricemeyer, this is the first time it has actually been proven. It’s unclear whether all asexual species use the same genetic process, but he hopes future research will help answer that question.

Understanding these genetic processes could lead to many applications, from genetically modifying crops to treating diseases, Ricemeyer said. Cancer, he noted, is a disease in which a cloned cell line accumulates mutations that cause it to outgrow and crowd out non-mutated cell lines. Therefore, the cloning ability of the Amazon molly fish could help fight a major health threat to humans.