Schoen Daniel J, Ashman Tia-Lynn
Department of Biology, McGill University, 1205 Avenue Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada.
Evolution. 1995 Feb;49(1):131-139. doi: 10.1111/j.1558-5646.1995.tb05965.x.
The component parts of modular organisms often show interspecific variation in their longevity. In plants, the flower is an example of such a structure. Models are developed in this paper to predict optimal floral longevity (the optimal length of time that flowers should remain open and functional) under a variety of conditions. A tradeoff involving allocation of resources to floral construction versus floral maintenance is assumed. The main model variables are the rate at which pollen and seed fitness accrue over time (fitness-accrual rates) and the daily cost of maintaining an existing flower relative to the cost of constructing a new one (floral maintenance cost). Long-lived flowers are selected when fitness-accrual rates and floral maintenance costs are low, whereas short-lived flowers are selected when fitness-accrual rates and floral maintenance costs are high. Dichogamy favors longer-lived flowers relative to homogamy, whereas nonindependence among flowers in their attractiveness to pollinators (attraction to flower clusters) selects for shorter-lived flowers. Reduction in floral maintenance costs later on in the flower's life favors longer-lived flowers. Observations on the dissemination and receipt of pollen in individual flowers over time, together with measurements of corolla respiration and nectar sugar production rate are required to test the model quantitatively. The parameters important to the evolution of optimal floral longevity (i.e., maintenance and construction costs, and fitness-accrual rates) may be general features of evolution of optimal longevities of other repeated structures.
模块化生物体的组成部分在寿命方面往往表现出种间差异。在植物中，花就是这样一种结构的例子。本文建立了模型，以预测在各种条件下的最佳花期寿命（花朵应保持开放和功能正常的最佳时长）。假定存在一种权衡，即资源在花的构建与维持之间的分配。主要的模型变量是花粉和种子适合度随时间积累的速率（适合度积累速率），以及维持一朵现存花的每日成本与构建一朵新花的成本之比（花的维持成本）。当适合度积累速率和花的维持成本较低时，选择长寿命的花；而当适合度积累速率和花的维持成本较高时，选择短寿命的花。与同型花相比，雌雄异熟有利于寿命更长的花，而花朵对传粉者的吸引力（对花簇的吸引力）之间的非独立性则选择寿命较短的花。花在后期维持成本的降低有利于寿命更长的花。需要对单朵花随时间推移的花粉传播和接受情况进行观察，以及对花冠呼吸和花蜜糖分产生速率进行测量，以便对该模型进行定量测试。对最佳花期寿命进化重要的参数（即维持和构建成本以及适合度积累速率）可能是其他重复结构最佳寿命进化的普遍特征。
