Sex Allocation

Sex Allocation

Sex Allocation

Sex Allocation


Recent decades have witnessed an explosion of theoretical and empirical studies of sex allocation, transforming how we understand the allocation of resources to male and female reproduction in vertebrates, invertebrates, protozoa, and plants. In this landmark book, Stuart West synthesizes the vast literature on sex allocation, providing the conceptual framework the field has been lacking and demonstrating how sex-allocation studies can shed light on broader questions in evolutionary and behavioral biology.

West clarifies fundamental misconceptions in the application of theory to empirical data. He examines the field's successes and failures, and describes the research areas where much important work is yet to be done. West reveals how a shared underlying theoretical framework unites findings of sex-ratio variation across a huge range of life forms, from malarial parasites and hermaphroditic worms to sex-changing fish and mammals. He shows how research on sex allocation has been central to many critical questions and controversies in evolutionary and behavioral biology, and he argues that sex-allocation research serves as a key testing ground for different theoretical approaches and can help resolve debates about social evolution, parent-offspring conflict, genomic conflict, and levels of selection.

Certain to become the defining book on the subject for the next generation of researchers, Sex Allocation explains why the study of sex allocation provides an ideal model system for advancing our understanding of the constraints on adaptation among all living things in the natural world.


R. A. Fisher (1930) clearly was the pathbreaker in sex ratio

—Charnov 1982, p. 13

Fisher's theory of equal investment provides the basic null model for sex allocation theory, but it is also the foundation for all subsequent theoretical developments. This theory has firm theoretical foundations, established both before and after Fisher's influential work. However, attempts to test Fisher's prediction of equal investment in the sexes will usually be in vain, because the conditions required for this are likely to be extremely rare. Instead, it is more productive to test the frequency-dependent nature of Fisher's theory by perturbing the population sex ratio and then examining whether it evolves back toward equal investment. Some species with unusual life histories also provide useful opportunities for testing Fisher's theory.

2.1 introduction

Fisher (1930) provided an explanation for why males and females should be produced in approximately equal numbers, as is observed in many animal species. However, it has recently been shown that this theory was probably widely accepted at the time and had been developed previously by others (Edwards 1998, 2000). in particular, Darwin (1871) had provided a related verbal explanation, and Düsing (1883, 1884a, 1884b) had provided a formal mathematic model.

In the next section of this chapter, I describe the theory for equal investment in the sexes as presented by Fisher. Although Fisher may not have been the first to solve this problem, his treatment was, typically, extremely succinct and, perhaps atypically, very clear, grasping the importance of reproductive value, and it has been highly influential in the field of evolutionary biology in general. I then briefly consider the formal development of this theory, both before and . . .

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