Does early season browsing influence the effect of self-pollination in scarlet gilia?

Herbivore damage can have indirect effects on plant fitness by influencing other important plant-animal interactions, such as pollination biology. For example, damage to floral and vegetative structures may influence the pattern of pollen movement within and among individual plants. In obligately outcrossing species, enhanced movement of self pollen (geitonogamy) can negatively impact fitness if self pollen clogs stigmas, interferes with stylar transmitting tracts, usurps ovules, or increases fruit abortion. We investigated whether early season browsing affects the fitness cost of self-pollination in the obligately outcrossing species scarlet gilia, Ipomopsis aggregata, using clipping and emasculation treatments. We found that clipping significantly reduced the production of flowers, fruits, and seeds whereas emasculation significantly increased the production of these components of female fitness. In addition, we detected a significant interaction between the clipping and emasculation treatments when considering four components of fitness simultaneously; emasculation led to an increase in the fitness of unclipped plants but not clipped plants. We propose two nonexclusive mechanisms to explain this pattern. First, damaged plants may experience reduced self-pollination due to reductions in pollinator visitation or effectiveness. Alternatively, damaged plants may simply lack the resources (or the ability to allocate resources) to benefit from emasculation. Our results support the notion that herbivory can have indirect effects on plant fitness through effects on other plant-animal interactions.