Dissertation Research: The Evolution of Mutualism and Cost-Benefit Analysis: Selection on Extrafloral Nectar Traits of Chamaecrista Fasciculata

共生关系是物种之间的生态相互作用，在这种相互作用中，两个物种都受益。本项目将评估花外花蜜介导的蚂蚁与山雀间互惠共生的成本-收益框架的假设和预测。野外实验将评估四个假设：1)提供互利性状（花外花蜜）是昂贵的；2)花外花蜜通过减少被花蜜吸引的蚂蚁对食草动物的伤害提供了好处；3)成本和收益的平衡产生了有利于中间最优的稳定选择；4)成本和收益的操纵应该改变选择最优的值。此外，本项目将评估成本效益框架是否可以解释花外花蜜性状的地理差异。该性状的地理差异将被调查，种群之间的差异与不同选择最优的存在一致的假设将通过互惠移植实验进行验证。共生现象无处不在，但对其背后过程的理论和机制理解进展缓慢。在用于解释互惠共生进化的模型中，成本-收益方法是理解互惠共生中涉及的适应性特征进化的最普遍和最合适的框架。本项目将评估成本效益方法的假设和预测，以考虑蚂蚁与美国东部一种常见的一年生植物- - -山雀豆- - -之间的互惠关系。本研究为今后探讨互惠性状的选择模式提供了重要的实证依据。

Rausher 9800876 Mutualisms are ecological interactions between species in which both species benefit from the interaction. This project will evaluate the assumptions and predictions of the cost-benefit framework for the extrafloral nectar-mediated mutualism between ants and Chamaecrista fasciculata, the partridge pea. A field experiment will evaluate four assumptions: 1) the mutualistic trait (extrafloral nectar) is costly to provide, 2) the extrafloral nectar provides a benefit through reduction of herbivore damage by ants attracted to the nectar, 3) the balance of costs and benefits produces stabilizing selection favoring an intermediate optimum, and 4) manipulation of costs and benefits should change the value of the selective optimum. In addition, this project will assess whether the cost-benefit framework can explain geographic variation in extrafloral nectar traits in C. fasciculata. Geographic variation in the trait will be surveyed, and the hypothesis that variation between populations is consistent with the presence of different selective optima will be tested using a reciprocal transplant experiment. Mutualisms are ubiquitous, but theoretical and mechanistic understanding of the processes that underlie them has progressed slowly. Of the models that have been used to explain the evolution of mutualisms, the cost-benefit approach is the most general and the most appropriate framework for understanding the evolution of adaptive traits involved in mutualisms. This project will evaluate the assumptions and predictions of the cost-benefit approach in regard to a mutualism between ants and a common annual plant of the eastern United States, Chamaecrista fasciculata (the partridge pea). Data from this project should provide an important empirical basis for future discussion of the pattern of selection on mutualistic traits.