Selection on pollen and pistil traits during pollen competition is affected by both sexual conflict and mixed mating...

Although much attention has focused on the diversity of plant mating systems, only a few studies have considered the joint effects of mating system and sexual conflict in plant evolution. In mixed-mating Collinsia heterophylla, a sexual conflict over timing of stigma receptivity is proposed: pollen with a capacity to induce early onset of stigma receptivity secures paternity for early-arriving pollen (at the expense of reduced maternal seed set), whereas late onset of stigma receptivity mitigates the negative effects of early-arriving pollen. Here we investigated whether selection on pollen and pistil traits involved in sexual conflict is affected by the presence of both outcross- and self-pollen (mixed mating) during pollen competition.

We conducted two-donor crosses at different floral developmental stages to explore male fitness (siring ability) and female fitness (seed set) in relation to male and female identity, pollen and pistil traits, and type of competitor pollen (outcross vs. self).

Late-fertilizing pollen rather than rapidly growing pollen tubes was most successful in terms of siring success, especially in competition with self-pollen after pollination at early floral stages. Late stigma receptivity increased seed set after early-stage pollinations, in agreement with selection against antagonistic pollen.

Selection on pollen and pistil traits in C. heterophylla is affected by both sexual conflict and mixed mating, suggesting the importance of jointly considering these factors in plant evolution.