Can sexual conflict drive transitions to asexuality? Female resistance to fertilization in a facultatively parthenogenetic insect

Facultatively parthenogenetic animals could help reveal the role of sexual
conflict in the evolution of sex. Although each female can reproduce both
sexually (producing sons and daughters from fertilized eggs) and asexually
(typically producing only daughters from unfertilized eggs), these animals
often form distinct sexual and asexual populations. We hypothesized that
asexual populations are maintained through female resistance as well as
the decay of male traits. We tested this via experimental crosses between
individuals descended from multiple natural sexual and asexual populations
of the facultatively parthenogenic stick-insect Megacrania batesii. We
found that male-paired females descended from asexual populations produced
strongly female-biased offspring sex-ratios resulting from reduced
fertilization rates. This effect was not driven by incompatibility between
diverged genotypes but, rather, by both genotypic and maternal effects on
fertilization rate. Furthermore, when females from asexual populations
mated and produced sons, those sons had poor fertilization success when
paired with resistant females, consistent with male trait decay. Our
results suggest that resistance to fertilization resulting from both
maternal and genotypic effects, along with male sexual trait decay, can
hinder the invasion of asexual populations by males. Sexual conflict could
thus play a role in the establishment and maintenance of asexual
populations.