Collaborative Research: Eucalypt Hybrid Zones as "Sinks" for Herbivores: Responses of Pests to Natural Hybrids

对于植物-食草动物相互作用的研究，杂交区代表了自然实验，其中基于遗传的防御通过回交变得混乱。杨树病虫害研究表明，杨树病虫害主要集中在杂交区，杂交区内主要集中在回交树上。来自没有杂交带的水系的害虫比来自杂交带的害虫对亲本树种的表现更好。这些数据表明，高度易感宿主（即自然产生的复杂杂交）不仅支持大多数害虫种群，而且它们的存在可能导致害虫物种失去或永远无法进化出应对亲本树种更大抗性的能力。这项工作的一个含义是，敏感杂交种可用于管理虫害动态在林业和农业。由于本课题的基础和应用意义，本项目将在第二个系统桉树中研究这种现象（汇假设）的普遍性，其中杂交是常见的。研究人员将与桉树系统学家、遗传学家和生态学家合作，研究几个著名的自然杂交系统中的害虫动态。将讨论以下问题：杂交桉树是否会成为食草动物的水槽，从而使一小部分潜在寄主支持大多数害虫种群？2. 如果复杂的杂交品种更容易受到一种害虫的影响，那么它们是否也更容易受到不同种类昆虫的影响呢？3. 杂交带的存在与否会影响纯寄主区的害虫密度吗？这些问题将在一个自然系统中得到解决，即拥有已知基因型树木的普通花园，并通过记录昆虫对独立于研究收集的亲本和杂交植物标本的攻击。除了杨木之外，这些问题的答案还没有在任何系统中得到检验，这对于理解植物和害虫的生态和进化相互作用应该是至关重要的。

For studies of plant-herbivore interactions, hybrid zones represent natural experiments in which genetic-based defenses have become scrambled through backcrossing. Studies of insect pests of cottonwoods (Populus) show that pests are concentrated in hybrid zones and, within the zone, on backcrossed trees. Pests from river systems without hybrid zones perform better on the parent tree species than do pests from areas with hybrid zones. These data suggest that highly susceptible hosts (i.e., naturally occuring complex hybrids) not only support most of the pest population, their presence may result in pest species either losing or never evolving the ability to deal with the greater resistance of the parental tree species. An implication of this work is that susceptible hybrids can be used to manage pest dynamics in forestry and agriculture. Because of the basic and applied implications of this topic, this project will examine the generality of this phenomenon (the Sink Hypothesis) in a second system, Eucalyptus, in which hybridization is common. The researchers will collaborate with eucalypt systematists, geneticists, and ecologists to study pest dynamics in several well known natural hybrid systems. The following questions will be addressed: 1. Are hybrid eucalypts sinks for herbivores such that a small proportion of potential hosts support most of the pest population? 2. If complex hybrids are more susceptible to one pest, are they also more susceptible to very different insect guilds? 3. Does the presence or absence of hybrid zones affect pest densities in the pure host zone? These questions will be addressed in a natural system, common gardens with trees of known genotypes, and by documenting insect attacks on herbarium specimens of parents and hybrids collected independent of the study. Answers to these questions have not been examined for any system besides cottonwoods and should be fundamentally important in understanding the ecological and evolutionary interactions of plants and pests.