Sex-differential resistance and tolerance to herbivory in a gynodioecious wild strawberry

We explore the effects of,ender dimorphism on resistance (damage avoidance) and tolerance (growth and fitness compensation) to a flower bud clipping weevil in a gynodioecious wild strawberry. Using both natural populations and a common garden, we document pervasive hermaphrodite-biased damage and identify several floral traits associated with resistance. Lower flower number, lower pollen production per flower, and earlier flowering date were associated with higher resistance. Because the sex morphs do not differ in flower number or flowering time, the presence of pollen is the main factor determining sex-differential resistance. We confirmed that simulated clipping was a good surrogate for weevil clipping, and we used simulated clipping to assess sex-morph- and sex-function-specific tolerance. We found that females were less tolerant than hermaphrodites in terms of seed and fruit production, but the sex morphs were similarly unable to compensate fully in flower production. Hermaphrodites showed some ability to compensate in pollen per flower, but this was not large enough to offset flower losses, leading to net undercompensation for pollen per plant. We evaluated potential mechanisms for tolerance and found that the number of reserve buds was the most consistent predictor of tolerance. Finally, we found that herbivory shifted sex expression of hermaphrodites toward greater femaleness via both plastic changes in allocation and direct effects of loss of male-functioning flowers. Our work indicates that the effects of herbivory on sexual system evolution can include sexual phenotype-biased herbivore damage and sex-dependent tolerance, as well as herbivory-induced changes in hermaphrodite sex allocation. In addition, this study suggests that pollen production is subject to selection via herbivores that opposes selection mediated by pollinators.