Mixed Mating System in Agalinis neoscotica (Scrophulariaceae) with Bud Pollination and Delayed Pollen Germination

Abstract

Many species of angiosperms have mixed mating systems in which a portion of progeny result from self-fertilization and some from outcrossing. We show that Agalinis neoscotica has evolved a novel set of developmental and morphological characters in the flower that assure self-pollination without sacrificing the opportunity for outcrossing. Pollinator exclusion, emasculation tests, and controlled self- and cross-pollinations conducted at three field sites indicate that A. neoscotica is self-compatible. An overall mean pollen-ovule ratio of 128.5 for four populations indicates facultative selfing and indicates that self-fertilization occurred. An estimation of the mating system, using two enzyme loci in each of two natural populations, verifies that selfing occurs in each population, but neither population is completely selfing. Seeds of A. neoscotica are produced by a mix of self-fertilization and cross-fertilization. Observations of buds and flowers of A. neoscotica show that this species differs from its close relatives by precocious self-pollination in bud, thus assuring reproduction in the absence of pollinators, and in three characteristics that provide an opportunity for outcrossing: delayed germination of self pollen, presentation of additional stigmatic area, and lengthened period of anthesis. These results indicate that examination of preanthesis buds and flowers throughout anthesis is necessary for understanding the modes of selfing involved in mixed mating systems.