The Evolution of Clonal Diversity in Poeciliopsis

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Abstract

Despite the elegant body of theoretical literature on sexuality, recently reviewed by Williams (1975) and Maynard Smith (1978), very little empirical data exist to assess this “contest of ideas.” I will not attempt in this chapter to address the question, “Why is there sex?” Instead, I will examine a common assumption in most of these theoretical studies—that asexual populations lack genetic variation. It is commonly argued that asexual reproduction is an evolutionary dead end, that the absence of recombinational variability results in genetic inflexibility and sure extinction in a changing environment. The clonal genomes of asexual organisms are looked upon as rigid structures that can only change through mutation, and most mutations are deleterious (Muller, 1964). Despite the occasional success of some asexual populations, the long-term prospects appear grim (White, 1978). Yet, recent genetic studies have reported abundant clonal diversity in a number of asexually reproducing organisms [see reviews by Parker (1979a), Vepsalainen and Jarvinen (1979), and Vrijenhoek (1979a)]. What then is the source of this clonal diversity and how might it contribute to the ecological and evolutionary success of asexual populations?