Biology Department, Acadia University, Wolfville, Nova Scotia B4P 2R6 Canada.
Am J Bot. 2013 Feb;100(2):357-64. doi: 10.3732/ajb.1200603. Epub 2013 Jan 17.
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.
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.
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.
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.
在雌雄异株物种中，雄性偏食性被认为是选择提高雌性生殖成本（减少攻击）的结果。这种预测的实证支持在分类学上受到限制，并充满了例外。资源分配到繁殖的物候变化可能会以性别特异性的方式改变功能之间的权衡，并可能消除雄性偏食性。
我们调查了在新斯科舍省的 Ilex glabra 自然种群中，与繁殖期有关的繁殖、生长和防御之间的权衡变化，以及雌性是否比雄性更具有抗性和更低的耐受性（在受到伤害时保持适应度）。我们在 2006 年开花期间和之后以及 2007 年开花前对植物进行部分或全部去叶处理，并在 2007 年测量它们的生长和生殖产量。我们使用从去叶处理中获得的叶片上发现的叶片损伤比例来评估对草食性的抗性。
与理论预测相反，我们没有发现雄性偏食性。雄性比雌性在开花前后部分去叶时更具耐受性。无论性别如何，植物要么在部分去叶后完全或过度补偿，要么在完全去叶后补偿不足，除了在开花前去叶的情况。我们发现抗性和耐受性之间存在弱正相关，而不是权衡。
与繁殖物候相关的损伤时间会影响对草食性的抗性和耐受性，在评估关于生物相互作用的性别二态性的预测时必须考虑到这一点。
