Asexual reproduction can negatively impact evolution

In the animal kingdom, offspring are produced via two main reproductive pathways: sexual, through the fertilization between male and female gametes, and asexual, when offspring emerge through a single unfertilized egg. Parthenogenesis is a form of asexual reproduction in which females pass on their genes without a male being involved. 

A new study led the University of Lausanne in Switzerland in collaboration with the University of Cologne in Germany has found that parthenogenesis can negatively affect the genome evolution of the animals that practice it, by reducing genetic diversity and leading to adaptation problems.

“The shift from sexual reproduction to parthenogenesis has occurred repeatedly in animals, but how the loss of sex affects genome evolution remains poorly understood,” the study authors wrote. Through genetic analyses of asexually reproducing Timema (a genus of stick insects native to western North America that includes both sexually and asexually reproducing species), the scientists discovered that, in the long term, these insects cannot pass on beneficial mutations as efficiently as their sexually reproducing relatives.

Like humans and other animals, Timema have a double set of chromosomes. The extent to which these two genomes differ is called “heterozygosity.” During parthenogenesis, this difference is lost and the two genome copies become very similar. This reduces variability and leads to genetically uniform populations, which find it more difficult to adapt to their environments. 

“The results show that genetic exchange during sexual reproduction promotes the speed of adaptation and genetic diversity in the insects’ natural populations,” said study co-author Dr. Jens Bast, a professor of Ecology and Evolution at the University of Cologne.

“By using replicated sexual-parthenogenetic comparisons, our study reveals how the absence of sex affects genome evolution in natural populations, providing empirical support for the negative consequences of parthenogenesis as predicted by theory,” the authors concluded.

The study is published in the journal Science Advances.

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By Andrei Ionescu, Earth.com Staff Writer