The Mating System and Microevolution

Abstract

Mating systems and the selective forces that have molded them have held an important place in evolutionary theory since the time of Charles Darwin. Darwin himself paid considerable attention to the evolutionary consequences of mating systems and he noted an association in both plants and animals between sessile habit and hermaphroditism (Darwin, 1876). This askpect of his theory of natural selection has since been extended by many investigators who have identified two main features of the ability to self-fertilize that have direct adaptive value. These are: (1) the existence of fertilization insurance under many different circumstances, such as in habitats where environmental conditions are often unfavorable for gamete dispersal, or when potential mates are scarce due to low population density (Stebbins 1959; Baker 1953; Lefebvre 1970) and (2) the existence of an isolating barrier to gene flow between differently adapted populations which occupy closely adjacent but unlike habitats (Kannenberg and Allard 1967; Antonovics 1968). In this paper I wish to discuss still another feature of the ability to self-=fertilize that has important implications in evolution, namely, that regulation of the amount of inbreeding plays a major role in adjusting the manner in which genetic variability is organized in populations.