Michael Wade

This book presents the first unified conceptual and statistical framework for understanding the evolution of reproductive strategies. Using the concept of the opportunity for sexual selection, the authors illustrate how and why sexual selection, though restricted to one sex and opposed in the other, is one of the strongest and fastest of all evolutionary forces. They offer a statistical framework for studying mating system evolution and apply it to patterns of alternative mating strategies. In doing so, they provide a method for quantifying how the strength of sexual selection is affected by the ecological and life history processes that influence females' spatial and temporal clustering and reproductive schedules. Directly challenging verbal evolutionary models that attempt to explain reproductive behavior without quantitative reference to evolutionary genetics, this book establishes a more solid theoretical foundation for the field. Among the weaknesses the authors find in the existing data is the apparent ubiquity of condition-dependent mating tactics. They identify factors likely to contribute to the evolution of alternative mating strategies--which they argue are more common than generally believed--and illustrate how to measure the strength of selection acting on them. Lastly, they offer predictions on the covariation of mating systems and strategies, consider the underlying developmental biology behind male polyphenism, and propose directions for future research. Informed by genetics, this is a comprehensive and rigorous new approach to explaining mating systems and strategies that will influence a wide swath of evolutionary biology.

1930; Haldane, 1954). Selection causes observable changes within a generation in the means, variances and covariances of phenotypic distributions. Thus selection can be described in purely phenotypic terms without recourse to the inheritance of characters. In contrast, evolutionary response to selection, for example, the change in phenotypic mean from one generation to the next, certainly does depend on inheritance. In the following sections we show how knowledge of inheritance can be combined with purely phenotypic measures of selection to predict evolutionary response to selection. By distinguishing between selection and response to selection we can measure selection on characters whose mode of inheritance may be unknown and make prediction of evolutionary response a separate issue. Thus knowledge of inheritance is essential for complete

In this paper, we use measures of selection developed by quantitative geneticists and some new results (Arnold and Wade, 1984) to analyze multiple episodes of selection in natural populations ofamphibians, reptiles, and insects. These examples show how different methods of data collection influence the potential for relating field observations to formal evolutionary theory.We adhere to the Darwinian tradition of distinguishing between natural and sexual selection (Darwin, 1859, 1871; Ghiselin, 1974). We viewsexualselection as selection arising from variance in mating success and natural selection as arising from variance in other components offitness. The justification for this formal distinction is developed by Wade (1979), Lande (1980), Wade and Arnold (1980), Arnold and Houck (1982) and Arnold

In this paper, we use a model by Slatkin (1977) to investigate the genetic effects of extinction and recolonization for a species whose population structure consists of an array of local demes with some migration among them. In particular, we consider the conditions under which extinction and recolonization might enhance or diminish gene flow and increase or decrease the rate of genetic differentiation relative to the static case with no extinctions. We explicitly take into account the age‐structure that is established within the array of populations by the extinction and colonization process. We also consider two different models of the colonization process, the so‐called “migrant pool” and “propagule pool” models. Our theoretical studies indicate that the genetic effects of extinction and colonization depend upon the relative magnitudes of K, the number of individuals founding new colonies, and 2Nm, twice the number of …

Indirect genetic effects (IGEs) are environmental influences on the phenotype of one individual that are due to the expression of genes in a different, conspecific, individual. Historically, work has focused on the influence of parents on offspring but recent advances have extended this perspective to interactions among other relatives and even unrelated individuals. IGEs lead to complicated pathways of inheritance, where environmental sources of variation can be transmitted across generations and therefore contribute to evolutionary change. The existence of IGEs alters the genotype-phenotype relationship, changing the evolutionary process in some dramatic and non-intuitive ways.

Group selection is defined as that process of genetic change which is caused by the differential extinction or proliferation of groups of organisms. A very large proportion of the literature pertaining to group selection consists of theoretical papers; the genetic problems of group selection have been addressed from many different mathematical viewpoints. The general conclusion has been that, although group selection is possible, it cannot override the effects of individual selection within populations except for a highly restricted set of parameter values. Since it is unlikely that conditions in natural populations would fall within the bounds imposed by the models, group selection, by and large, has been considered an insignificant force for evolutionary change. These theoretical conclusions and the assumptions from which they have been derived are reexamined in the light of recent empirical studies of group selection …

Over the last two decades, research into epistasis has seen explosive growth and has moved the focus of research in evolutionary genetics from a traditional additive approach. We now know the effects of genes are rarely independent, and to reach a fuller understanding of the process of evolution we need to look at gene interactions as well as gene-environment interactions. This book is an overview of non-additive evolutionary genetics, integrating all work to date on all levels of evolutionary investigation of the importance of epistasis in the evolutionary process in general. It includes a historical perspective on this emerging field, in-depth discussion of terminology, discussions of the effects of epistasis at several different levels of biological organization and combinations of theoretical and experimental approaches to analysis.

We discuss the necessary and sufficient conditions for identifying the cause of natural selection on a phenotypic trait. We reexamine the observational methods recently proposed for measuring selection in natural populations and illustrate why the multivariate analysis of selection is insufficient for identifying the causal agents of selection. We discuss how the observational approach of multivariate selection analysis can be complemented by experimental manipulations of the phenotypic distribution and the environment to identify not only how selection is operating on the phenotypic distribution but also why it operates in the observed manner. A significant point of departure of our work from recent discussions is in regard to the role of the environment in the study of natural selection. Instead of viewing the environment as a source of unwanted variation that obscures the relationship between phenotype and fitness, we …

In this paper we define sexual selection on males as the variance in numbers of mates per male and show how the intensity of this selection is affected by male sexual behaviour, female choice, sex ratio, and modes of sperm precedence. This definition coincides with Darwin's conception of sexual selection but differs from some post-Darwinian views. For systems of single-male paternity, we show that the intensity of total selection on male reproductive success equals the intensity of natural selection on female fertility, times the sex ratio, plus the intensity of sexual selection on males. The absolute intensity of sexual selection is unaffected by the system of sperm precedence. The application of the results to field studies is discussed.

Darwin (1878) suggested in The Origin of Species (p. 230-233) that selection between families or communities had given rise to sterile castes in the social insects. He argued that sterility could not be favored directly by selection among individuals but that parents or communities might benefit, in terms of reproductive success, from the presence of sterile individuals. It is clear from his arguments that Darwin believed that selection among groups could result in a change in the types of individuals within a species. It was much later that Wright (1931) perceived intergroup selection as one of the primary forces controlling evolutionary change. He stated that the only practicable method of bringing about a rapid and non-self-terminating evolutionary advance would be through the subdivision of populations into isolated and differentiating groups, among which selection could be practiced.Haldane (1932) and Wright (1945 …

In this paper I illustrate the theoretical relationship among several different models of selection in structured populations, soft selection, hard selection, kin selection, and group selection, by using the covariance formulations of Li (1967) and Price (1970, 1972) to partition the operation of selection into within-and between-group components. This partitioning of covariance can be directly extended from the single-locus population genetic models derived in this paper to the description of selection within and between groups for continuously distributed, quantitative traits of the type presently under investigation in several research programs of kin and group selection. In addition, because of the algebraic relationship between the covariance and the coefficient of linear regression, regression coefficients can be used to evaluate the relative importance of selection within and between groups in these models of subdivided …

Bateman (1948) in his early studies of intrasexual selection in Drosophila melanogaster concluded that the variance in the number of mates is" the only important cause of the sex difference in variance of fertility"(p. 363). He also suggested that"... a sex difference in variance in fertility is, therefore, a measure of the sex difference in intensity of selection"(p. 353). A more recent discussion of sexual selection (Trivers 1972) has emphasized the role of parental investment in offspring as the cause of sexual selection by means of competition for mates." What governs the operation of sexual selection is the relative parental investment of the sexes in their offspring. Competition for mates usually characterizes males because males usually invest almost nothing in their offspring"(p. 141). Trivers specifically excludes those energies expended in intrasexual competition when evaluating parental investment. Trivers furthermore …

We critically review the two major theories of adaptive evolution developed early in this century, Wright's shifting balance theory and Fisher's large population size theory, in light of novel findings from field observations, laboratory experiments, and theoretical research conducted over the past 15 years. Ecological studies of metapopulations have established that the processes of local extinction and colonization of demes are relatively common in natural populations of many species and theoretical population genetic models have shown that these ecological processes have genetic consequences within and among local demes. Within demes, random genetic drift converts nonadditive genetic variance into additive genetic variance, increasing, rather than limiting, the potential for adaptation to local environments. For this reason, the genetic differences that arise by drift among demes, can be augmented by local …

Maternal effects can play an important role in a diversity of ecological and evolutionary processes such as population dynamics, phenotypic plasticity, niche construction, life-history evolution and the evolutionary response to selection. However, although maternal effects were defined by quantitative geneticists well over half a century ago, there remains some confusion over exactly what phenomena should be characterized as maternal effects and, more importantly, why it matters and how they are defined. We suggest a definition of maternal effects as the causal influence of the maternal genotype or phenotype on the offspring phenotype. This definition differs from some definitions in that it treats maternal effects as a phenomenon, not as a statistical construct. The causal link to maternal genotype or phenotype is the critical component of this definition providing the link between maternal effects and evolutionary and …

THREE genetically discrete male morphs coexist in Paracerceis sculpta, a Gulf of California marine isopod 1–5. The large α males defend harems within intertidal sponges, the smaller β males mimic female behaviour and morphology, and the tiny γ males invade and sequester themselves within large harems. If selection is responsible for maintaining this polymorphism, then the mean fitness of each male morph must be equal over time 6–9. Here we report that average reproductive success is equivalent among the three male morphs in monthly population samples collected over two years. We have investigated the total opportunity for sexual selection within and among morphs, and find that< 0.10% of the total opportunity for sexual selection occurs among morphs. Furthermore, alleles responsible for the expression of this polymorphism conform to the Hardy-Weinberg equilibrium, indicating the absence of …