Although dioecy in flowering plants is mostly thought to have evolved because of its function as an outbreeding system (Lewis 1942; Stebbins 1950; Baker 1959; Charlesworth and Charlesworth 1978; and see Willson 1979), other possible explanations based on the ecological and energetic advantages of unisexual individuals have been offered (Darwin 1877; Janzen 1970; Bawa and Opler 1975: Charnov et al. 1976; Freeman et al. 1980; Symon 1980). Willson (1979) and Bawa (1980) pointed out some of the limitations of the classic genetic hypothesis for the evolution of dioecy, and discussed the potential role of sexual selection in the evolution of separate male and female individuals. Horovitz and Harding (1972). Lloyd (1974, 1979), and Horovitz (1978) have also discussed the theoretical basis of gender specialization of hermaphrodites. The proposal presented here is a specific hypothesis for the evolution of dioecy in entomophilous groups. It does not displace the importance of the genetic benefits of outcrossing as a factor in the evolution of unisexuality, but rather provides a mechanism that may have operated in conjunction with the fitness rewards resulting from the production of genetically diverse progeny.
Beach, J. H. and Bawa, K. S., "Role of Pollinators in the Evolution of Dioecy from Distyly" (1980). Ba. Paper 1.
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