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，在这些实验中，基于基因的防御通过回交而变得争先恐后。对杨树害虫的研究表明，害虫主要集中在杂交区，在杂交区内主要发生在回交树上。来自没有杂交带的河流系统的害虫比来自有杂交带的地区的害虫在母树物种上表现得更好。这些数据表明，高度敏感的寄主(即自然产生的复杂杂交种)不仅支持大多数害虫种群，它们的存在可能导致害虫物种失去或永远不会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，敏感的杂交种可以用于管理林业和农业中的害虫动态。由于这一主题的基本和应用意义，本项目将在第二个系统Eucalyptus中研究这种现象(Sink假说)的普遍性，在该系统中，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：1.杂交桉树汇聚食草动物，是否使得一小部分潜在寄主支持大多数害虫种群？2.如果复杂的杂交种更容易受到一种害虫的影响，它们是否也更容易受到不同昆虫协会的影响？3.杂交区的存在或不存在是否会影响纯寄主区的害虫密度？这些问题将在一个自然系统中解决，即拥有已知基因型树的普通花园，并记录昆虫对独立于研究收集的双亲和杂交种标本标本的攻击。这些问题的答案除了棉白杨以外，没有任何系统被研究过，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.