Departamento de Biologia Geral, Centro de Ciências Biológicas e da Saúde, Universidade Estadual de Montes Claros, Montes Claros, Minas Gerais, Brazil.
PLoS One. 2012;7(10):e46896. doi: 10.1371/journal.pone.0046896. Epub 2012 Oct 4.
Dioecy represents a source of variation in plant quality to herbivores due to sexual differences in intensity and timing of resource allocation to growth, defense and reproduction. Male plants have higher growth rates and should be more susceptible to herbivores than females, due to a lower investment in defense and reproduction.
METHODOLOGY/PRINCIPAL FINDINGS: We compared resource investment to growth and reproduction and its consequences to herbivore attack on three Baccharis species along one year (B. dracunculifolia, B. ramosissima, and B. concinna). Phenological patterns presented by the three species of Baccharis were quite different over time, but the number of fourth-level shoots and plant growth rate did not differ between sexes in any studied species. Intersexual difference in reproductive investment was only observed for B. concinna, with female individuals supporting higher inflorescence density than male individuals throughout the year. Gall abundance on the three Baccharis species was not influenced by plant sex. However, all plant traits evaluated here positively influenced the gall abundance on B. concinna, whereas only the number of fourth-level shoots positively influenced gall abundance on B. ramosissima and B. dracunculifolia.
CONCLUSIONS/SIGNIFICANCE: The absence of differential reproductive allocation may have contributed to similar growth and shoot production between the sexes, with bottom-up effects resulting in gender similarities in gall abundance patterns. The number of fourth-level shoots, an indicator of meristem availability to herbivores, was the most important driver of the abundance of the galling insects regardless of host plant gender or species. Albeit the absence of intersexual variation in insect gall abundance is uncommon in the literature, the detailed study of the exceptions may bring more light to understand the mechanisms and processes behind such trend.
雌雄异株代表了植物质量对食草动物的一个变化来源，因为资源分配到生长、防御和繁殖的强度和时间存在性别差异。由于在防御和繁殖方面的投资较低，雄性植物的生长速度应该比雌性植物更高，因此更容易受到食草动物的影响。
方法/主要发现：我们比较了三种 Baccharis 物种（B. dracunculifolia、B. ramosissima 和 B. concinna）在一年中对生长和繁殖的资源投入及其对食草动物攻击的后果。Baccharis 三种植物的物候模式随时间变化差异很大，但在任何研究物种中，雌雄个体的第四级枝数和植物生长率没有差异。只有在 B. concinna 中观察到雌性个体在繁殖投资上的雌雄间差异，因为雌性个体全年比雄性个体支持更高的花序密度。三种 Baccharis 物种上的瘿蜂数量不受植物性别的影响。然而，这里评估的所有植物特征都对 B. concinna 上的瘿蜂数量有积极影响，而只有第四级枝数对 B. ramosissima 和 B. dracunculifolia 上的瘿蜂数量有积极影响。
结论/意义：缺乏差异的生殖分配可能导致雌雄个体的生长和枝数相似，从而导致瘿蜂丰度模式出现由下而上的性别相似性。第四级枝数，是对食草动物可用分生组织的指标，是影响瘿蜂丰度的最重要驱动因素，而不论宿主植物的性别或物种如何。尽管昆虫瘿蜂丰度在雌雄间没有差异在文献中并不常见，但对异常情况的详细研究可能会更好地理解这种趋势背后的机制和过程。
