Self- and Cross-Fertilization in Plants. III. Methods for Studying Modes and Functional Aspects of Self-Fertilization

Abstract

Procedures are described for partitioning the selfing rate into contributions resulting from the different modes of chasmogamous selfing-geitonogamous, facilitated, prior, competing, and delayed-and for examining several functional aspects of self-fertilization associated with the different modes-reproductive assurance, degree of seed and pollen discounting, and relative abilities of cross- and self-pollen to fertilize ovules. The procedures involve floral manipulations-e.g., exclusion of pollinators, emasculation, and covering of stigmas-and typically require joint estimation of the mating system parameters in manipulated and unmanipulated plants. Two methods of mating system estimation are discussed, the first in which manipulations and selfing rate estimates are made using random parent plants that are resident in the population, and the second using plants with unique genotypes introduced from a separate population. The asymptotic variances of estimators for the different modes of selfing are compared for each method, and advantages and disadvantages of each method are presented. The method of partitioning selfing into modes is illustrated using data from a natural population of the annual plant Impatiens pallida. Selfing in the chasmogamous flowers of this species is shown to result primarily from geitonogamy.