Effects of soil resources on expression of a sexual conflict over timing of stigma receptivity in a mixed-mating plant

While environmental factors strongly influence plant growth and reproduction, less is known about environmental effects on sexual selection and sexual conflict. In this study on mixed-mating Collinsia heterophylla we investigated whether soil resource environment affected traits associated with sexual conflict. In C. heterophylla a sexual conflict over timing of stigma receptivity occurs. Early stigma receptivity benefits pollen parents by securing paternity while late stigma receptivity benefits female fitness in terms of increased seed production. We performed hand-pollinations combining recipients and donors grown either in high or low resource environments and asked whether these treatments influenced sexual conflict traits - recipient- and donor-based influence on timing of stigma receptivity - and conflict costs related to reduced early seed production. We also asked whether resource environment affected eight traits related to general fitness and mating system. Sexual conflict-associated traits - timing of stigma receptivity and seed production - were generally unaffected by resource environment. While no universal effect of resources was detected, we did observe donor-specific responses to environment, suggesting that environment can nonetheless contribute to variation in timing of stigma receptivity. Recipients grown under low resources showed pronounced differences among donors for number of seeds per capsule, indicating that recipients favour some donors over others under resource-low conditions. Moreover, high resources increased number of flowers but reduced pollen germination rate, while other traits were unaffected, indicating variation in the response to resource environment for fitness- and mating system-traits. Our results suggest that even though soil resource environment had a low impact on the sexual conflict traits and related costs in C. heterophylla, it generated variability in pollen donor-influence on this trait and in recipient sorting among donors. Thus, it is possible that both sexual conflict and sexual selection is affected by environmental factors not only in animals but also in plants.