The Ecology of Geitonogamous Pollination

Working as a natural historian in the 1700s, C.K. Sprengel wrote a pioneering book demonstrating that many hermaphroditic species require pollinator visits in order to produce seed (see Chapters 1 and 2). He did not provide a scientific explanation as to why cross-pollination is important, but in the next century Darwin, H. and F. Muller, and others proposed that various outcrossing mechanisms have evolved to avoid selfing and the consequences of inbreeding (Darwin, 1876; see Baker, 1983). Darwin also recognized that the potential for selfing is greatest in species with massive floral displays because having many flowers promotes the transfer of self-pollen to other flowers on the same genetic individual (geitonogamy). Following Darwin’s lead, many authors have suggested that the avoidance of selfing has been a major factor in the evolution of traits such as dioecy, self-incompatibility, monoecy, temporal separation of male and female organs (dichogamy), spatial separation of anthers and stigmas within flowers (herkogamy), and having few open flowers per day (see reviews by Arroyo, 1976; Lloyd, 1979; Bawa and Beach, 1981; Willson, 1983; Wyatt, 1983; Richards, 1986; Charlesworth and Charlesworth, 1987; Thomson and Brunet, 1990; de Jong, et al., 1992a; Harder and Barrett 1995; Hodges, 1995; also see Chapters 6, 8, and 14).