Optimal Reaction Norms and Genetic Constraints in the Evolution of Plant Size in Ipomoea purpurea

这个项目的目标是试图理解一种模式生物，牵牛花，在多大程度上能最优地适应它遇到的各种环境。具体地说，这个项目试图在不同的环境中描述几个特征的经验最优值，然后确定自然种群是否已经进化到在各自的环境中表现出这些值。该项目还试图描述可能阻止人口进化到这些最优值的任何限制因素。首先将调查紫荆草通常遇到的自然环境范围的特征。利用这些信息，将进行两个田间试验，在土壤养分水平梯度或竞争强度梯度下种植紫荆。自然选择的模式作用于与植物生长和大小有关的性状，将被测量，以确定这些性状的平均值与它们在每种环境中的最优值之间的距离。一组育种和选择实验将提供任何遗传约束的特征，以阻止进化到这些最优状态，这些约束的重要性将通过计算机模拟进行评估。自然选择的进化是在有利的（选择如何起作用）和可能的（由生物体的遗传决定）之间的妥协。虽然生物学家在了解生活在简单、受控环境中的模式生物（如果蝇）的进化方面取得了很大进展，但对植物和动物种群对复杂自然环境的进化反应知之甚少。这个项目的主要目标是开始提供对生物体在遇到复杂环境时的这种反应的理解。

9707223 Rausher The goal of this project is to attempt to understand the degree to which a model organism, the morning glory Ipomorea purpurea, is optimally adapted to various environments it encounters. Specifically, this project seeks to characterize empirically the optimal value for several traits in different environments and then determine whether natural populations have evolved to exhibit those values in the respective environments. The project also seeks to characterize any constraints that may prevent populations from evolving to those optimal values. Characteristics of the range of natural environments normally encountered by I. purpurea will initially be surveyed. Using this information, two field experiments will be conducted in which I. purpurea is grown either a gradient of soil nutrient levels or a gradient of competitive intensity. The pattern of natural selection acting on traits related to plant growth and size will be measured to determine how far the means of these traits are from their optima in each environment. A set of breeding and selection experiments will provide a characterization of any genetic constraints acting to prevent evolution toward these optima, and the importance of these constraints will be evaluated by computer simulation. Evolution by natural selection is a compromise between what is favored (how selection acts) and what is possible (determined by the genetics of organisms). While biologists have made great strides understanding evolution in model organisms (e.g. fruit flies) living in simple, controlled environments, much less is known about the evolutionary responses of plant and animal populations to complex natural environments. The broad aim of this project is to begin to provide an understanding of such a response in an organism that typically encounters a complex environment.