The ontogeny of plant defense: general patterns and genetic variation

植物从幼苗期发育到成熟期的过程中发生了巨大的变化，这一过程被称为个体发育。对于涉及防御草食动物的特征，这些个体发育模式是自然群落动态的关键方面，推动植物和草食动物之间的相互作用。植物防御特征包括有毒的化学物质和物理屏障，如阻止草食动物生长的刺、刺和毛，以及减少草食动物负面影响的植物特征，如受损后再生的能力。毒素的浓度、刺和刺的密度以及再生速率都可能随着植物的发育而变化，这些变化会对植物遭受的食草动物损害水平产生影响。例如，一些物种的植物在苗期对食草动物的防御能力很低，因此，在这一脆弱时期，食草动物的危害最高。相比之下，其他物种的植物作为幼苗比成年植物对食草动物的保护相对更好，导致较老植物的损害水平更高。植物防御性状的个体发育模式是常见的，并已在60多种植物中被记载。然而，一个普遍的模式还没有出现。物种间的差异可能是由于植物物种在生活史策略(木本植物与草本植物)、主要防御特征(毒素、刺、再生等)和所研究的植物年龄方面的差异造成的。这项研究的主要目标有两个：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，揭示植物防御个体发育的一般模式。这些统计分析还将揭示哪些因素导致物种之间的差异(木本与草本、防御特性的种类、植物年龄等)。2)利用芬兰西南部银桦的大规模田间试验，研究植物防御个体发育中的遗传变异。第二个目标将这项工作放在更广泛的进化背景下，通过考虑防御的个体发育是否能够对自然选择做出反应。如果植物防御中的个体发育模式要随着自然选择的反应而进化，那么特征的个体发育模式必须有遗传变异。然而，这一关键假设很少得到检验。这项研究将与伦敦皇家霍洛威大学生物科学学院的朱莉娅·科里切娃合作完成。Koricheva博士是国际公认的在生态学和进化论中使用荟萃分析进行合成的专家。她反复使用荟萃分析来调查她的主要专业领域--植物-食草动物相互作用--的关键假说。此外，她开发了分析工具--图形向量分析，将用于了解植物防御特性在个体发育过程中的变化。最后，科里切娃博士在芬兰西南部设计并领导了一项大规模的田间实验，该实验将被用来测量白桦树的遗传变异。因此，这次合作将利用我在美国科罗拉多大学的博士论文中对植物防御进行调查时在植物防御个体发育方面的特殊专业知识，以及Koricheva博士在荟萃分析和图形载体分析方面的专业知识。通过阐明个体发育在植物防御和食草性中的作用，本研究将对我们理解植物防御的进化做出重要贡献。

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.