Data from: Adaptive molecular evolution of a defence gene in sexual but not functionally asexual evening primroses

Theory predicts that sexual reproduction provides evolutionary advantages
over asexual reproduction by reducing mutational load and increasing
adaptive potential. Here, we test the latter prediction in the context of
plant defences against pathogens because pathogens frequently reduce plant
fitness and drive the evolution of plant defences. Specifically, we ask
whether sexual evening primrose plant lineages (Onagraceae) have faster
rates of adaptive molecular evolution and altered gene expression of a
class I chitinase, a gene implicated in defence against pathogens, than
functionally asexual evening primrose lineages. We found that the ratio of
amino acid to silent substitutions (Ka/Ks = 0.19 vs. 0.11 for sexual and
asexual lineages, respectively), the number of sites identified to be
under positive selection (four vs. zero for sexual and asexual lineages,
respectively) and the expression of chitinase were all higher in sexual
than in asexual lineages. Our results are congruent with the conclusion
that a loss of sexual recombination and segregation in the Onagraceae
negatively affects adaptive structural and potentially regulatory
evolution of a plant defence protein.