Résumé
Evolutionary transitions to asexuality are often studied by comparing
asexuals found in nature with closely related sexuals. Yet, asexuals
sampled in nature may represent only the most successful lineages and
therefore provide limited information about the average properties of
newly emerging asexuals. These properties are crucial in determining the
success of asexual lineages and hence the frequency with which transitions
to asexual life cycles evolve. Here, we generate new asexual lineages of f
Daphnia pulex through contagious asexuality, in which rare males from
obligate asexual lineages transmit asexuality to new lineages by mating
with sexual females. Unlike asexuals found in nature, most new lineages
were capable of both sexual and asexual reproduction (facultative
asexuality) and produced non-identical (i.e., non-clonal) daughters when
reproducing asexually. They also showed reduced fertility compared to
natural asexuals, especially when reproducing asexually, which is expected
to reduce the success rate of sex-asex transitions in nature. Taken
together, these results suggest that creating new asexual lineages by
contagion is more complex than previously thought and may result in
diverse, non-clonal offspring, on which subsequent selection can act. If
general, such initial fitness valleys associated with sex-asex transitions
may be key to resolving the evolutionary “paradox of sex”.