Desert annual plants have a strong timing constraint on reproduction due to their brief and variable flowering season. Self-fertilizing species can avoid the risk of unpredictable pollination via reproductive assurance. While the majority of annuals self-fertilize, it is not uncommon to find congeneric obligate outcrossers and selfers growing together. This suggests that the benefits and costs of these mating strategies tradeoff, promoting their maintenance in the same habitat. Our research addresses the question, how do reproductive trade-offs promote outcrossing in some species and self-fertilization in others?  An ideal system in which to examine the ecology of reproductive strategies in desert ecosystems is within the genus Camissonia (Onagraceae). Self-fertilization has evolved many times in this group and sister species with contrasting reproductive strategies frequently overlap in their distributions. In previous field studies we have demonstrated that variable timing of pollinator activity plays a role in determining fitness in selfers and outcrossers. Outcrossers experienced a decrease in reproductive success when they experienced a mismatch with pollinator phenology but outperformed selfers when there was later season flowering and no mismatch. In this study we examine how pollen and resource availability mediates plant fitness in pairs of selfing and outcrossing sister taxa.  

Results/Conclusions

We present a greenhouse experiment exploring the role of pollen and resource availability in determining reproductive success within selfing and outcrossing strategies.  Specifically, we explored variation in growth, physiological, and reproductive traits.  We have demonstrated that growth rates and physiological traits are influenced by variation in water availability. Specifically, outcrossing species had a greater decrease in physiological functioning as a result of resource limitation compared to selfing species. A decrease in resource availability was expressed by a reduction in flower size and number rather than a reduction in ovule or seed number. In addition, we manipulated pollen availability by controlling flower/fruit ratios. Decreasing pollen availability led to a greater increase in future reproductive allocation in selfers compared to outcrossers. This study highlights the potential for decreased fitness in outcrossing species resulting from increased allocation to floral structures and reduced fertilization opportunities.