Effects of foliar herbivory by insects on the fitness of Raphanus raphanistrum: Damage can increase male fitness

Generally, effects of herbivory on plant fitness have been measured in term s of female reproductive success (seed production). However, male plant fit ness, defined as the number of seeds sired by pollen, contributes half of t he genes to the next generation and is therefore crucial to the evolution o f natural plant populations. This is the first study to examine effects of insect herbivory on both male and female plant reproductive success. Throug h controlled field and greenhouse experiments and genetic paternity analysi s, we found that foliar damage by insects caused a range of responses by pl ants. In one environment, damaged plants had greater success as male parent s than undamaged plants. Neither effects on pollen competitive ability nor pollinator visitation patterns could explain the greater siring success of these damaged plants. Success of damaged plants as male parents appeared to be due primarily to changes in allocation to flowers versus seeds after da mage. Damaged plants produced more flowers early in the season, but not mor e seeds, than undamaged plants. Based on total seed production, male fitnes s measures from the first third of the season, and flower production, we es timated that damaged and undamaged plants had equal total reproductive succ ess at the end of the season in this environment. In a second, richer envir onment, damaged and undamaged plants had equal male and female plant fitnes s, and no traits differed significantly between the treatments. Equal total reproductive success may not be ecologically or evolutionarily equivalent if it is achieved differentially through male versus female fitness. Genes from damaged plants dispersed through pollen may escape attack from herbivo res, if such attack is correlated spatially from year to year.