Frank, S. A. 1983. A hierarchical view of sex-ratio patterns. The Florida Entomologist 66:42-75.

Most organisms have two sexes; thus it is reasonable to ask what is the ratio of the sexes, and does this ratio fluctuate in a predictable manner. Basic researchers have long recognized that the sex ratio is a phenotypic trait of an organism, and therefore may be subject to natural selection. In addition, it has been widely noted that (i) the relative fitness of a male versus a female ranges widely according to a variety of ecological factors (e.g., size of individual, local sex ratio, inbreeding), implying that the selection of sex-ratio traits should be strong; and (ii) relative to other traits studied by behavioral ecologists, sex ratios can often be measured with a high degree of precision. Hence, the subject of sex ratios is ideal for testing the efficacy of natural selection, and for testing our understanding of the selective process. Applied researchers also have a long history of interest in sex ratios. Efficiency of livestock breeding would be greatly enhanced by control over the sex ratio; mass-rearing of parasites as biological control agents is often improved by a female-biased sex ratio; and causing a male-biased sex ratio in a population of pests would aid in reducing the amount of damage.

This paper is an introduction to a way of viewing sex-ratio puzzles that has had some success—both theoretically and empirically—and points out some of the difficulties of sex-ratio problems. After a methodology has been developed, the following questions will be addressed: What sex-ratio patterns are observed in nature? What are the causes and what are the ecological correlates of the patterns? What sort of logic is required to explain each pattern? What general themes underlie the patterns? Some assumptions and extensions of the theory are discussed in the appendix.


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