Stick insect on a plant

This stick insect in the Timema genus reproduces asexually despite a significant genetic cost. Credit: Bart Zijlstra www.bartzijlstra.com

Evolution

Sex pays off for stick insects despite costs

Species comparison confirms downsides of asexual reproduction.

Asexual reproduction might be convenient — with no need to find or fight for mates — but it can have undesirable genetic results. Sex keeps evolution moving, reshuffling the genetic deck every time new offspring are conceived. Now, a study of stick insects supports classical theories about the perils of life without sex.

Jens Bast at the University of Lausanne in Switzerland and his colleagues extracted RNA from ten species of stick insect in the genus Timema. All are physically and ecologically similar, but five reproduce sexually and five reproduce asexually. Compared with the sexually reproducing insects, the asexual insects’ genomes contained more harmful mutations. The asexual insects were also genetically more similar to each other, meaning that a weakness in one was more likely to be shared by the whole population.

However, it’s not all doom and gloom: the oldest asexual lineages are almost 2 million years old.