Effects of Foliar Herbivory on Male and Female Reproductive Traits of Wild Radish,raphanus Raphanistrum

In this study, we examined how foliar herbivory affected the relative allocation to male and female reproductive traits in a hermaphroditic plant. In two experiments, one in the greenhouse and the other in a growth chamber, leaves of full sibling plants of the annual wild radish, Raphanus raphanistrum, received one of four damage treatments to leaves (0, 25% two types, or 50% leaf area removal). We controlled natural damage by Pieris rapae larvae through the use of clip cages. Measurements of both male and female reproductive characters were made on a series of flowers produced by each plant over its lifetime. We measured pollen production, pollen size, ovule number, ovule size, petal size, nectar production, and sugar content. Effects of herbivory on plant phenology were also assessed. At the end of the experiment, we quantified total flower production, fruit production, number of seeds and fruit, and seed and vegetative biomass. In general, male reproductive characters were more affected than female characters by herbivory. Leaf herbivory reduced pollen number and pollen size, whereas ovule size and number were not affected. Petal size, which we also classify more as a male trait, decreased with herbivory. Plants were generally able to completely compensate for herbivory in the total number of flowers and fruit they produced; however, fewer fruits were found in the heaviest damage treatment in the growth chamber experiment. We discuss alternative explanations for this pattern based on developmental constraints and adaptive responses. In summary, male fitness traits were much more strongly affected by herbivory than were female traits; full compensation in seed production after herbivory may come at the cost of male reproductive success in these hermaphroditic plants.