Host shifts and host-associated differentiation in herbivorous insects: ecological causes and consequences

地球上生命最明显的特征之一是其惊人的多样性--至少有100万个物种已为科学界所知，也许还有多达3000万个物种有待发现。然而，一些谱系的多样性比其他谱系丰富得多，解释这种不同的成功是进化生态学中最基本的问题之一。其中最引人注目的是以植物为食的昆虫和攻击它们的寄生虫--多达一半的动物物种可能属于其中一个或另一个群体。以植物为食的昆虫和寄生蜂进化成功的一个原因可能是它们倾向于进化出专门的食物。食物通过寄主转移(在食物中添加新的寄主植物)进化，然后新的多样性通过寄主相关分化(HAD)进化，其中单一的饮食通才分化形成一对新的寄主-专家物种。*我们发现，虽然寄主转移和HAD是常见的，但它们不是普遍的，不同的谱系可以不同的时间和速度以及通过不同的机制经历这些过程。我的研究项目试图通过研究以两种常见的加拿大黄花为食的不同昆虫集合，来了解控制寄主转移和HAD发生的生态因素。通过对比进化成对寄主专家的物种和继续以多面手的身份进食的物种的生态学和种群遗传学，我们可以测试有关支持或阻碍多样性的力量的假说。我们目前的重点是昆虫对寄主植物个体之间的特征变异的偏好如何推动它们对寄主植物物种之间的变异的进化反应。对寄主迁移和HAD的预测性了解将有助于我们了解地球生物多样性的起源，以及预测和管理昆虫对农业和农林系统中新寄主的攻击。我们还将在HAD工作的基础上，测试这样一个假设，即随着植物进化出更强的耐受性，昆虫的毒力降低，食草动物对宿主植物的影响会随着进化时间的推移而减弱。如果这是真的，由寄主转移产生的新的昆虫-食草动物协会和HAD应该比古代的影响更大。这一点很重要，因为这种新的昆虫-食草动物协会也是入侵物种传播的结果，并在全球范围内造成巨大的且不断增加的生态和经济代价。**

One of the most obvious features of life on Earth is its astonishing diversity - at least a million species are known to science, and perhaps as many as 30 million more remain to be discovered. Some lineages have diversified much more abundantly than others, though, and accounting for this differential success is one of the most fundamental questions in evolutionary ecology. Among the most spectacular examples of "hyperdiversity" are plant-feeding insects and the parasitoids that attack them - as many as half of all animal species may belong to one or the other of these groups. One reason for the evolutionary success of plant-feeding insects and parasitoids may be their tendency to evolve specialized diets. Diets evolve via host-shifting (adding new host plants to diet), and then new diversity evolves by host-associated differentiation (HAD), in which a single diet generalist diverges to form a new pair of host-specialist species.***      While host-shifting and HAD are common, they are not universal, and different lineages can undergo these processes at different times and rates and by different mechanisms. My research program seeks to understand the ecological factors that control the occurrence of host-shifting and HAD, by studying the diverse set of insects feeding on two common Canadian goldenrods. By contrasting the ecology and population genetics of species that are evolving pairs of host specialists, vs. those that continue to feed as generalists, we can test hypotheses about forces that favour or retard diversification. Our current focus is on the way insect preferences for trait variation among host plant individuals can drive their evolutionary response to variation between host plant species. A predictive understanding of host-shifting and HAD will help us understand the origin of Earth's biodiversity, as well as to anticipate and manage attack by insects on novel hosts in agricultural and agroforestry systems. We will also build on our HAD work by testing the hypothesis that the impact of herbivores on their host plants lessens over evolutionary time, as the plants evolve greater tolerance and the insects reduced virulence. If this is true, novel insect-herbivore associations generated by host-shifting and HAD should show higher impact than ancient ones. This is important, because such novel insect-herbivore associations also result from the spread of invasive species and have enormous and increasing ecological and economic costs worldwide. **