Direction of Life History Evolution in Drosophila mojavensis

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Abstract

Studies of the genetic basis for life history evolution involving analysis of demographic change in response to patterns of environmental variability have yet to provide a general explanation for the diversity of life histories often observed among species. Part of this problem is due to the lack of information about the forces actually responsible for causing the genetic variation observed in natural populations, without which we cannot evaluate the significance of the variation measured or the precise outcome in long-term life history evolution. Adaptation to environmental variability can lead to different equilibrium life histories all with equivalent fitnesses (Schaffer and Rosenzweig, 1977). The form of life history expected will depend on the pattern of environmental variation and degree of correlation among life history traits (Tuljapurkar, 1988; Orzack and Tuljapurkar, 1989). Only when observed genetic variation and covariation in components of fitness can be associated with the causes in nature responsible for their maintenance will understanding of the microevolutionary processes directing life history evolution be possible (Istock et al., 1976; Reznick and Endler, 1982; Etges, 1989a).