Collaborative Research: Effects of Herbivory and Stress on Seaweed Resource Acquisition, Allocation Patterns, and Fitness

本研究将探讨具有重要生态意义的潮间带岩藻（Fucus gardneri）如何分配资源，以响应两个关键环境变量的变化，草食和干燥压力（如潮间带经历的高）。这些变量通常是独立研究的，但它们对海藻的综合影响在自然界中一定很重要。藻类必须“决定”如何将获得的能量分配给生长、繁殖、威慑（例如抗草食化学物质）和其他关键的生活史功能，特别是当压力降低了资源获取能力时。虽然陆生植物的资源分配模式正在被深入研究，但几乎没有类似的研究存在于藻类，尽管它们易于操作，丰富，与维管植物有有趣的系统发育对比，并且在近岸海洋生态系统中起着重要作用。此外，关于分配模式对海藻适应性的影响，我们几乎一无所知。这里的适应度表示为有限的人口增长率。将生理学与适应性联系起来是至关重要的，因为生长甚至繁殖的变化可能不会转化为对海藻种群的影响。在这个项目中，将首先开发一个简单的模型，平衡资源获取（作为净初级生产）与所有已知的岩藻类主要资源分配汇（生长、繁殖、植黑素、储存、分泌、食草动物损失）。该模型将为比较墨角藻对田间胁迫和草食梯度的生理反应以及在中生态环境中操纵时的生理反应提供工具。该研究将包括：1)观察岩藻类的野外种群，量化其在草食和胁迫下的自然梯度分配模式的变化；2)生理测量实验室的净初级生产(沼生植物和沉)和模型的其他术语field-grown菌体;3)在野外和实验室环境中对胁迫关键变量（重现时间、干燥）和草食性进行控制，并对这些条件下菌体的分配模式进行评估；4)发展人口统计模型，通过在胁迫和草食的潮间带梯度中测量的菌体生活史转变来估计人口增长率。还将对被认为含有抗草食化合物的提取物的化学成分和威慑作用进行初步研究。该方法旨在评估涉及资源分配的几个具体问题及其对潮间带海藻种群的影响，这些问题比海藻对压力和草食的反应具有更广泛的影响。虽然以前几乎所有关于生物资源分配的研究都假设资源获取是恒定的，但本项目将通过测量净初级产量来检验这一假设。假设在压力条件下，净初级产量随潮间带梯度而变化。如果这个假设是错误的，那么如果不考虑资源获取的变化，分配权衡比较将是无效的。还假设存在一个临界压力水平，超过该水平，资源汇之间的重新分配是不可能的。对资源重新分配能力的生理限制很少得到解决。最后，在成年生物中表现出来的分配模式通常被认为代表了适应度或适应性的一个重要方面。然而，成虫期可能不是影响种群增长率和种群持久性的最重要的生活史阶段。人口模型的敏感性/弹性分析将确定哪些生活史转变（例如，成虫生存和繁殖与补充）对种群增长率最关键，因此，成虫体内的分配模式对海藻种群增长是否重要。-这项研究将为解决海藻资源分配问题提供第一个综合方法，并将证明环境的严酷程度（生物或非生物）反映在藻类的表现上。通过这种方式，它将提供物理变化（例如在全球变暖期间可能发生的变化）与藻类个体生长和繁殖以及海藻种群持续存在的能力之间的联系。

Williams This research will investigate how an ecologically important intertidal fucoid alga (Fucus gardneri) allocates resources in response to variation in two key environmental variables, herbivory and desiccation stress (such as that experienced high in the intertidal zone). These variables are typically studied independently, yet it is their combined effect on seaweeds that must be important in nature. Algae must make "decisions" about how to allocate acquired energy to growth, reproduction, deterrency (e.g., anti-herbivore chemicals), and other key life-history functions, particularly when stress reduces resource acquisition capacity. While resource allocation patterns are being investigated intensively in terrestrial plants, almost no comparable work exists for algae, despite their ease of manipulation, abundance, interesting phylogenetic contrast to vascular plants, and important roles in nearshore marine ecosystems. In addition, virtually nothing is known about the consequences of allocation patterns to seaweed fitness. Fitness here is represented as the finite rate of population growth. Linking physiology to fitness is critical because changes in growth, or even reproduction, may not translate to effects on seaweed populations. In this project, a simple model that balances resource acquisition will be developed first (as Net Primary Production) against all known major resource allocation sinks for fucoids (growth, reproduction, phlorotannins, storage, exudation, loss to herbivores). This model will provide a tool to compare the physiological response of Fucus to gradients in stress and herbivory in the field and when manipulated in mesocosms. The research will involve: 1) observations of field populations of fucoids to quantify variation in their allocation patterns across natural gradients in herbivory and stress; 2) physiological measurements in the laboratory of Net Primary Production (emersed and immersed) and the other terms of the model for field-grown thalli; 3) manipulation both in the field and in laboratory mesocosms of the key variables of stress (emersion time, desiccation) and herbivory where thalli will be raised to reproductive size under these conditions, and then their allocation patterns will be assessed; and 4) development of demographic models to estimate population growth rates from life-history transitions measured in thalli across an intertidal gradient in stress and herbivory. Preliminary studies of the chemical composition and deterrency of extracts thought to contain anti-herbivore compounds will also be performed.The approach is designed to evaluate several specific issues involving resource allocation in, and its consequences for, intertidal seaweed populations that have broader implications than the response of seaweeds to stress and herbivory. Although virtually all previous studies of resource allocation in organisms assume that resource acquisition is constant, this project will test this assumption with measurements of Net Primary Production. Net Primary Production hypothetically varies across intertidal gradients in stressful conditions. If the assumption is false, allocation trade-off comparisons would not be valid without accounting for variation in resource acquisition. It is also hypothesized that there is a critical stress level above which reallocation among resource sinks is not possible. A physiological limit to the capacity to reallocate resources has rarely been addressed. Finally, allocation patterns demonstrated in adult organisms often are assumed to represent an important aspect of fitness or adaptedness. Yet, the adult phase might not be the most important life history stage in contributing to the population growth rate, and thus persistence of the populations. Sensitivity/elasticity analyses of the demographic models will determine which life history transitions (e.g., adult survival and reproduction versus recruitment) are most critical to the population growth rate, and thus, if allocation patterns within adults are important to seaweed population growth. . - This research will provide the first integrated approach to questions of resource allocation in seaweeds, and will demonstrate to what extent environmental harshness (biotic or abiotic) is reflected in algal performance. In this way, it will provide a link between physical changes (such as might occur during global warming) and the ability of algal individuals to grow and reproduce and seaweed populations to persist.