Chemical Defenses Against Floral Enemies: Costs and Benefits of Toxic Nectar to Nectar Robbing, Pollination, and Plant Fitness

在自然系统中，生物体面临着同时与互利者和拮抗者的直接和间接相互作用，但我们对这些竞争压力在形成表型性状进化中的相对重要性的理解仍然是初步的。例如，开花植物可能面临着吸引传粉者同时阻止花的敌人，如花蜜掠夺者的困境。因为强盗与传粉者竞争相同的资源（例如，花蜜），这可能是特别困难的植物进化的防御机制，是有效的对抗拮抗剂，而不也吓阻互惠。这项研究的目标是确定一种普遍存在但知之甚少的花的特性，有毒花蜜，如何影响与花蜜掠夺者和传粉者的相互作用，以及这些同时发生的相互作用如何塑造对这种表型特性的选择。有毒花蜜，或含有次级化合物的花蜜，是一种普遍存在的特性，可能会赋予对花掠夺者的抵抗力，但可能会以传粉者的吸引力为代价。目前，有毒花蜜的成本和效益尚不清楚。除了抗性特征，植物还可以通过耐受性来科普拮抗剂。传统上，抗性和耐受性的概念被用于指食草动物;然而，花蜜掠夺者，像食草动物一样，对植物适应性有深远的影响，植物很可能利用抗性和耐受性作为防御机制。通过研究花蜜性状的作用，如花蜜毒性和产量，作为对花蜜掠夺的抗性和耐受机制，拟议的研究将把抗性和耐受概念扩展到更广泛的植物-动物相互作用。这项工作的目的是了解有毒花蜜在互利互惠者之间相互作用的背景下的生态作用。（传粉者）和拮抗剂（花蜜强盗），并确定抗性和耐受性在多大程度上介导花蜜强盗对植物基因型的影响。这项研究将通过实验操纵钩吻的花蜜毒性，钩吻是一种多年生葡萄，其花蜜中含有生物碱，确定有毒花蜜对昆虫传粉者和强盗群落以及对雄性和雌性植物繁殖和后代成功的影响。此外，本研究还将对G.本研究利用已知花蜜毒性变异性的常绿植物，以确定花蜜掠夺对植物适合度的直接和间接影响，耐花蜜掠夺的遗传变异，以及在没有花蜜掠夺的情况下有毒花蜜的成本。该研究结合了田间实验和观察，以解决四个主要问题：1）花蜜毒性是否存在遗传变异？2)有毒花蜜是否通过增加植物对花蜜掠夺的抵抗力而不减少传粉者的吸引力而使植物受益？3)花蜜掠夺是否直接或间接地降低植物适合度？植物基因型对花蜜掠夺的抗性或耐受性是否存在差异？4）在没有掠夺的情况下，有毒花蜜的成本是否存在？这里提出的工作是新颖的，因为它在互利和对抗性访花者施加的联合选择力的背景下，整合了与普遍存在但知之甚少的花卉特征（有毒花蜜）相关的抗性的成本和收益。这项工作扩展了现有的概念框架，并提供了经验洞察的多样性的作用，一个单一的花卉性状可以服务，从吸引到防御。考虑更广泛的背景下，其中organismsevolve是我们的理解如何多物种的相互作用形状遗传和生物多样性在生态，微进化和宏观进化尺度的基础。

ADLER - 0211480In natural systems, organisms face simultaneous direct and indirect interactions with mutualists andantagonists, yet our understanding of the relative importance of these competing pressures inshaping the evolution of phenotypic traits is still rudimentary. For example, flowering plants mayface the dilemma of attracting pollinators while discouraging floral enemies, such as nectarrobbers. Because robbers are competing with pollinators for the same resource (e.g., nectar), it maybe particularly difficult for plants to evolve defensive mechanisms that are effective againstantagonists without also deterring mutualists. The goal of the proposed research is to determinehow a ubiquitous but poorly understood floral trait, toxic nectar, influences interactions with bothnectar robbers and pollinators, and how these simultaneous interactions shape selection on thisphenotypic trait.Toxic nectar, or nectar that contains secondary compounds, is a widespread trait that may conferresistance to floral robbers, but at a potential cost to pollinator attraction. Currently, the costs andbenefits of toxic nectar are unknown. In addition to resistance traits, plants may cope withantagonists via tolerance. The concepts of resistance and tolerance have traditionally been used inreference to herbivores; however, nectar robbers, like herbivores, have profound effects on plantfitness and plants are likely to use resistance and tolerance as defensive mechanisms againstrobbers. The proposed research will extend resistance and tolerance concepts to a wider range ofplant-animal interactions through an examination of the role of nectar traits, such as nectar toxicityand production, as mechanisms of resistance and tolerance to nectar robbing.The aim of this work is to understand the ecological role of toxic nectar within the context ofinteractions between mutualists (pollinators) and antagonists (nectar robbers), and to determine theextent to which resistance and tolerance mediate the impact of nectar robbers on plant genotypes.The research proposed will experimentally manipulate nectar toxicity in Gelsemium sempervirens,a perennial vine with documented alkaloids in its nectar, to determine the impact of toxic nectar onthe community of insect pollinators and robbers as well as on male and female plant reproductionand offspring success. In addition, this study will manipulate nectar robbing and pollination ingenotypes of G. sempervirens with known variability in nectar toxicity to determine the direct andindirect effects of nectar robbing on plant fitness, genetic variation in resistance and tolerance tonectar robbing, and costs of toxic nectar in the absence of nectar robbing. The research combinesmanipulative field experiments with observations to address four main questions: 1) Is theregenetic variation in nectar toxicity? 2) Does toxic nectar benefit plants by increasing resistance tonectar robbing without reducing pollinator attraction? 3) Does nectar robbing reduce plant fitnessdirectly or indirectly, and do plant genotypes vary in their resistance or tolerance of nectar robbing?and 4) Is there a cost of toxic nectar in the absence of robbing?The work proposed here is novel in that it integrates the costs and benefits of resistance associatedwith a ubiquitous but poorly understood floral trait, toxic nectar, in the context of joint forces ofselection exerted by both mutualistic and antagonistic floral visitors. This work extends an existingconceptual framework and provides empirical insight into the diversity of roles a single floral traitcan serve, from attraction to defense. Consideration of the broader context in which organismsevolve is fundamental to our understanding of how multiple-species interactions shape genetic andbiological diversity at ecological, microevolutionary, and macroevolutionary scales.