Predictors of male and female tolerance to insect herbivory in Raphanus raphanistrum

Traits associated with plant tolerance to herbivory are often thought to be those involved in resource acquisition, e.g., root biomass, leaf area, and photosynthetic rate. Plant resistance traits, like concentrations of secondary compounds, can also be negatively associated with tolerance. Few studies have,measured both tolerance and resistance traits in the same study to determine which are the best predictors of a plant's ability to tolerate insect,damage. Here, we measured simultaneously a large suite of traits on damaged and undamaged siblings in 10 families of greenhouse-grown Raphanus raphanistrum plants. Traits measured were: leaf area, root biomass, shoot biomass, photosynthetic rate, trichome density, total glucosinolate concentration, flowering rate, petal size, total number of flowers, and total number of seeds. Pieris rapae larvae were used to damage plants to 50% leaf area removal. Using multiple regression, we examined which traits were the best. predictors of tolerance. We considered both male tolerance (relative number of flowers produced by damaged and undamaged sibs) and female tolerance (relative number of seeds produced). We found that, generally, resistance traits were better predictors of both male and female tolerance than tolerance traits. Interestingly, we found that mate and female tolerance were not correlated, and that male tolerance was significantly less variable than female tolerance. We also found that measurements, of traits postdamage (induced state) were more informative than measurements on undamaged plants (constitutive state). Our results support the idea of a resistance/tolerance trade-off. In addition, our study suggests that there are conflicts in investment in male. vs. female fitness after damage.