The latest research published in the Proceedings of the National Academy of Sciences (PNAS) discussed the interesting work of Texas State researchers on the origins of Amazon mollies– an intriguing unisex fish species.
Renowned Texas state researchers Dr. Laura Alberici da Barbiano, Andrea Aspbury, Caitlin Gabor, Zachariah Gompert, and Chris Nice from the Texas State Department of Biology authored the study, titled, “Population genomics reveals a possible history of backcrossing and recombination in the gynogenetic fish Poecilia formosa.”
The clonal species of Amazon molly are unisexual – female only and are found in stagnant water along the coasts of Northern Mexico and South Texas. The usual mode of reproduction of Amazon mollies was mating with male Atlantic mollies or sailfin mollies; however, the development of eggs does not involve the incorporation of any genetic components from the males.
According to the studies conducted previously by the Texas State, the evolution of the Amazon mollies was mainly via hybrid cross of closely-related molly species approximately 100,000 years ago. However, the latest research suggested that the hybrid fish interbred with the members of the parent specie for many generations until it established itself as a clonal species with a far extensive genetic diversity than the original first-generation hybrid.
“This is not first time this hypothesis has been proposed, but this study has more specific data supporting the idea. It explains why people can make hybrids from the Amazon molly’s parent species, but not make Amazons. That indicates why they have more genetic variation.”
The research team concluded that the diversity of genetic material is the key to the persistence of the species. Vertebrates are very rarely unisexual species and are therefore at much higher risk of getting extinct with time due to limited genetic diversity.
“Something is going on with the genetic material. Instead of being strictly clonal, there’s more variation among the population. There’s some type of recombination in the background. When DNA gets repaired in a sexual species, there are two strands — one from mom and one from dad — that can be used to repair the damage. With a clonal species, when DNA is repaired there’s only one strand, so the outcome is different.”
There are a number of short-term benefits of unisexual reproduction in species —for example, a lesser amount of energy is required for the process of reproduction — but nevertheless, the sexual species are at far higher advantage of protecting and preventing genetic damage (since the genetic material is acquired from both the parents). But the diverse genetic material of the Amazon molly has helped in preventing the expected chromosomal decay over a long period of time. Gabor concluded with these words: “The door you can open up with this are questions about sexual versus asexual reproduction, and about the maintenance of sex. The Amazons have the asexual way, and they’ve been able to survive a long time.”