The ontogeny of plant defense: general patterns and genetic variation

植物在从幼苗发育到成熟的过程中发生了巨大的变化，这一过程被称为个体发育。对于涉及防御食草动物的性状，这些个体发生模式是自然群落动态的关键方面，驱动植物和食草动物之间的相互作用。植物防御特性包括有毒化学物质和物理屏障，如刺、刺和毛发，它们可以阻止食草动物，以及减少食草动物负面影响的植物特性，如在受到伤害后再生的能力。毒素的浓度、刺和刺的密度以及再生速度都可能随着植物的发育而变化，而这些变化对植物所经历的食草伤害水平有影响。例如，某些种类的植物在苗期对食草动物的防御能力较弱，因此，在这个脆弱的时期，食草动物的伤害是最大的。相比之下，其他种类的植物作为幼苗比成年植物更能抵御食草动物，导致老植物受到更高程度的伤害。植物防御性状的个体发生模式是常见的，已在60多种植物物种中得到证实。然而，一个普遍的模式并没有出现。物种间的变异可能具有显著的生物学意义，这是由植物物种之间的生活史策略（木本植物与草本植物）、主要防御性状（毒素、刺、再生等）和所研究的植物年龄的差异造成的。本研究有两个主要目标：1)利用强大的统计技术（荟萃分析和图形向量分析）综合现有文献，以揭示植物防御个体发生的一般模式。这些统计分析还将揭示哪些因素导致了物种之间的差异（木本与草本、种类防御性状、植物年龄等）。2)通过芬兰西南部白桦的大规模田间试验，探讨植物防御个体发生的遗传变异。第二个目标是通过考虑防御的个体发生是否可以响应自然选择，将这项工作置于更广泛的进化背景中。如果植物防御的个体发生模式是为了响应自然选择而进化的，那么在性状的个体发生模式中必然存在遗传变异。然而，这一关键假设很少得到验证。这项研究将与伦敦皇家霍洛威大学生物科学学院的Julia Koricheva合作完成。Koricheva博士是国际公认的在生态学和进化综合中使用元分析的专家。她反复使用元分析来调查她主要专业领域的关键假设，植物-草食动物相互作用。此外，她还开发了分析工具，图形矢量分析，将用于了解植物防御性状在个体发生过程中的变化。最后，Koricheva博士设计并领导了芬兰西南部的大规模野外实验，该实验将用于测量白桦的遗传变异。因此，这次合作将充分利用我在植物防御个体发生方面的特殊专业知识，这是我在科罗拉多大学（美国）的博士论文中对植物防御进行调查时发展起来的，以及Koricheva博士在元分析和图形矢量分析方面的专业知识。本研究将通过阐明个体发生在植物防御和草食中的作用，为我们对植物防御进化的认识做出重要贡献。

Plants change dramatically as they develop from young seedlings to the mature adult stage, a progression called ontogeny. For traits involved in defense against herbivores, these ontogenetic patterns are key aspects of natural community dynamics, driving interactions between plants and herbivores. Plant defense traits include toxic chemicals and physical barriers, such as thorns, spines, and hairs, that deter herbivores, as well as plant traits that reduce the negative impacts of herbivores, such as the ability to regrow following damage. Concentrations of toxins, densities of thorns and spines, and regrowth rate may all change as plants develop, and these changes have consequences for the levels of herbivore damage plants experience. For example, some species of plants produce few defenses against herbivores during the seedling stage, and consequently, damage by herbivores is the highest during this vulnerable period. In contrast, other species of plants are relatively better defended against herbivores as seedlings than they are as adult plants, leading to higher levels of damage in older plants. Ontogenetic patterns in plant defense traits are common and have been documented in over 60 plant species. Yet, a general pattern has failed to emerge. Variation among species is likely to be biologically significant, caused by differences among plant species in their life history strategies (woody vs. herbaceous plants), primary defense traits (toxins, thorns, regrowth, etc.), and plant ages studied. The proposed research addresses two primary goals: 1) To synthesize the current literature using powerful statistical techniques (meta-analysis and graphical vector analysis) in order to reveal general patterns in the ontogeny of plant defense. These statistical analyses will also reveal what factors contribute to the variation observed among species (woody vs. herbaceous, kind of defense traits, plant ages, etc.). 2) To examine genetic variation in the ontogeny of plant defense by using a large-scale field experiment with silver birch in southwestern Finland. The second goal puts this work into a broader evolutionary context by considering whether the ontogeny of defense can respond to natural selection. If ontogenetic patterns in plant defense are to evolve in response to natural selection, there must be genetic variation in the ontogenetic patterns of traits. This key assumption, however, has rarely been tested. This research will be done in collaboration with Julia Koricheva at the School of Biological Sciences, Royal Holloway University of London. Dr. Koricheva is an internationally recognized expert in the use of meta-analysis for synthesis in ecology and evolution. She has used meta-analysis repeatedly to investigate key hypotheses in her primary field of expertise, plant-herbivore interactions. Furthermore, she developed the analytical tool, graphical vector analysis, that will be used to understand how plant defense traits change during ontogeny. Finally, Dr. Koricheva designed and has led the large-scale field experiment in southwestern Finland that will be used to measure genetic variation in silver birch. This collaboration will thus capitalize on my particular expertise in the ontogeny of plant defense, developed during investigations of plant defense for my Ph.D. dissertation at the University of Colorado (USA), and Dr. Koricheva's expertise in meta-analysis and graphical vector analysis. This research will make a significant contribution to our understanding of the evolution of plant defense by elucidating the role of ontogeny in defense and herbivory.