Reproduction, growth, and defense trade-offs vary with gender and reproductive allocation in Ilex glabra (Aquifoliaceae).

PREMISE OF THE STUDY

Male-biased herbivory in dioecious species is expected as a consequence of selection for increased resistance (reduced attack) in the sex with higher reproductive costs-females. Empirical support of this prediction is taxonomically restricted and fraught with exceptions. Phenological changes in resource allocation to reproduction may change the trade-offs among functions in a sex-specific fashion, and may eliminate male-biased herbivory.

METHODS

We investigated variation in trade-offs among reproduction, growth, and defense in relation to the reproductive period, and whether females were more resistant and less tolerant (maintaining fitness upon damage) than males in a natural population of Ilex glabra in Nova Scotia. We subjected plants to partial or full defoliation treatments during and after flowering in 2006 and before flowering in 2007, and measured their growth and reproductive output in 2007. We assessed resistance to herbivory using the proportion of leaf damage found on leaves obtained from the defoliation treatment.

KEY RESULTS

Contrary to theoretical predictions, we did not find male-biased herbivory. Males were more tolerant than females to being partially defoliated before or after flowering. Regardless of sex, plants either fully or overcompensated after partial defoliation, and under-compensated in response to full defoliation, except when defoliated before flowering. Rather than a trade-off, we found a weak, positive correlation between resistance and tolerance.

CONCLUSION

The timing of damage in relation to reproductive phenology influences both resistance and tolerance to herbivory, which must be considered when assessing predictions about gender dimorphism of biotic interactions.