Effects of foliar herbivory on male and female reproductive traits of wildradish, Raphanus raphanistrum

In this study, we examined how foliar herbivory affected the relative alloc ation to male and female reproductive traits in a hermaphroditic plant. In two experiments, one in the greenhouse and the other in a growth chamber, l eaves of full sibling plants of the annual wild radish, Raphanus raphanistr um, received one of four damage treatments to leaves (0, 25% [two types], o r 50% leaf area removal). We controlled natural damage by Pieris rapae larv ae through the use of clip cages. Measurements of both male and female repr oductive characters were made on a series of flowers produced by each plant over its lifetime. We measured pollen production, pollen size, ovule numbe r, ovule size, petal size, nectar production, and sugar content. Effects of herbivory on plant phenology were also assessed. At the end of the experim ent, we quantified total flower production, fruit production, number of see ds and fruit, and seed and vegetative biomass. In general, male reproductive characters were more affected than female cha racters by herbivory. Leaf herbivory reduced pollen number and pollen size, whereas ovule size and number were not affected. Petal size, which we also classify mon as a male trait, decreased with herbivory. Plants were genera lly able to completely compensate for herbivory in the total number of flow ers and fruit they produced; however, fewer fruits were found in the heavie st damage treatment in the growth chamber experiment. We discuss alternativ e explanations for this pattern based on developmental constraints and adap tive responses. In summary, male fitness traits were much more strongly aff ected by herbivory than were female traits; full compensation in seed produ ction after herbivory may come at the cost of male reproductive success in these hermaphroditic plants.