THE EVOLUTION OF FLORAL LONGEVITY - RESOURCE-ALLOCATION TO MAINTENANCE VERSUS CONSTRUCTION OF REPEATED PARTS IN MODULAR ORGANISMS

The component parts of modular organisms often show interspecific vari ation in their longevity. In plants, the flower is an example of such a structure. Models are developed in this paper to predict optimal flo ral longevity (the optimal length of time that flowers should remain o pen and functional) under a variety of conditions. A tradeoff involvin g allocation of resources to floral construction versus floral mainten ance is assumed. The main model variables are the rate at which pollen and seed fitness accrue over time (fitness-accrual rates) and the dai ly cost of maintaining an existing flower relative to the cost of cons tructing a new one (floral maintenance cost). Long-lived flowers are s elected when fitness-accrual rates and floral maintenance costs are lo w, 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) s elects for shorter-lived flowers. Reduction in floral maintenance cost s later on in the flower's life favors longer-lived flowers. Observati ons on the dissemination and receipt of pollen in individual Bowers ov er time, together with measurements of corolla respiration and nectar sugar production rate are required to test the model quantitatively. T he parameters important to the evolution of optimal floral longevity ( i.e., maintenance and construction costs, and fitness-accrual rates) m ay be general features of evolution of optimal longevities of other re peated structures.