Evolutionary theory suggests that species favouring asexual reproduction will rapidly become extinct, as their genomes accumulate deadly mutations over time.
But a study on an Amazon fish has cast doubt on the rapidity of this decline.
Despite thousands of years of asexual reproduction, the genomes of the Amazon molly fish are remarkably stable and the species has survived.
Details of the work have been published in Nature Ecology and Evolution.
There are two fundamental ways in which new generations of life come to being – sexual and asexual reproduction.
Sexual reproduction relies on special reproductive male and female sex cells, the eggs and sperm, joining together during the process of fertilisation.
Each sex cell contains half the number of chromosomes of normal parent cells, then following fertilisation, when the egg and sperm fuse, the normal cell chromosome number is reinstated.
Asexual reproduction is different.
A life born of celibacy
Instead of creating a new generation by mixing equal measures of DNA from the mother and father, asexual reproduction dispenses with the male and instead creates new offspring containing an exact copy of the mother’s genome – natural maternal cloning, if you like.
This is an incredibly efficient way of creating new life. By not wasting genetic material on the creation of males, all offspring arising from asexual reproduction can go on to produce more.
But there is a downside. Because the progeny are genetic facsimiles of the mother they exhibit limited variability.
And genetic variability can provide a big advantage. It’s what allows populations to respond and overcome changes in environment and other selective pressures – it underpins survival of the fittest.
Sexual reproduction provides lots of scope to generate genetic variability; when pieces of individual chromosomes recombine as the eggs and sperm are formed and when the unique combinations of chromosomes are merged at fertilisation.