EvoLunch Seminar: Christoph Haag (University of Montpellier, FR)

Evolutionary transitions to asexuality are often studied by comparing asexuals found in nature with closely related sexuals. However, asexuals sampled in nature may represent only a small subset of the most successful lineages and may therefore contain limited information on the average properties of newly arising asexuals. Here, we generate new asexual lineages of two small crustaceans, Daphnia pulex and Artemia parthenogenetica, by contagious asexuality, where rare males from obligate asexual lineages transmit asexuality to new lineages ("neo-asexuals") by cross-mating with sexual females. In both species, we find that the newly created asexual lineages strongly differ from those sampled in nature, regarding their mode of asexual reproduction, loss of heterozygosity, recombination, and fitness. Together, these findings suggest that the creation of new asexual lineages through contagion may not be as straightforward as previously thought and may result in diverse, non-clonal offspring, on which subsequent selection may act. Our results also show the strength of laboratory-based experiments in complementing field-based studies, as the direction and degree of selection acting on novel asexual lineages can be inferred from the contrast between asexuals generated in the laboratory and older asexuals sampled in the field. More generally, I will discuss the importance of neo-asexuals for addressing the evolutionary “paradox of sex”.