Sex, Size and Gender Roles

Abstract

This book is an edited compendium of twenty chapters addressing the evolution, adaptive significance, and genetic and developmental basis of differences between the sexes in body size and morphology. General concepts and methodologies are introduced in Chapter 1, which also includes an overview of variation in sexual size dimorphism (SSD) with emphasis on extreme dimorphisms (i.e., dwarf males) and taxa not covered in subsequent chapters. Chapters 2-7 present new, comprehensive, comparative analyses of broad-scale patterns of SSD in mammals, birds, reptiles, amphibians, spiders, and insects, respectively. Chapters 8-15 comprise case studies of SSD within species or groups of closely related species. Flowering plants, insects, lizards, birds, and mammals are represented in this section. Chapters 16-20 emphasize proximate mechanisms underlying SSD and include theoretical explorations of anisogamy, genomic conflict, genomic imprinting, sex-linkage, and sex-specific gene expression, as well as experimental studies of sex-specific patterns of growth and development. Throughout the book, the emphasis is on testing hypotheses concerning the evolution and adaptive significance of SSD, and the importance of sexual selection on male size emerges as a common theme. However, this adaptationist approach is balanced by studies of proximate genetic, developmental, and physiological processes.

The evolution of parental cooperation in birds

“…We then also calculated absolute SDI by taking absolute values of the original SDI. Greater values of absolute SDI thus mean greater difference in body masses between sexes, suggesting differential selection acting on males and females that may indicate sexual selection (15,43). Extrapair paternity (EPP) was expressed as % of broods containing at least one extrapair offspring, in accordance with recent studies (64).…”

“…S2). First, intense sexual selection as indicated by extensive sexual size dimorphism (43) and high rates of extrapair paternity are consistently associated with low parental cooperation (Figs. 2 and 3).…”

Female monopolization mediates the relationship between pre- and postcopulatory sexual traits

“…55), we used body size measured as body mass in all vertebrate taxa except minnows (standard length) and a measure of body length that is widely used for each of the invertebrate taxa except dung beetles (body mass). The use of mass and linear size indices had no effect on the main results (Supplementary Note 2).…”

Evolution of sexual dimorphism in bill size and shape of hermit hummingbirds (Phaethornithinae): a role for ecological causation

“…Although evolutionary ecologists currently recognize competition as a force that can drive the evolution of differences between species through character displacement, the role of competition in driving the evolution of differences between sexes within a species is poorly understood (Hedrick & Temeles 1989;Shine 1989;Fairbairn et al 2007), even though Darwin (1871) hypothesized that some sexual dimorphisms in animals resulted from ecological causes in the form of resource partitioning. A major problem is the lack of unambiguous evidence in support of his hypothesis, despite numerous examples of sexual differences in resource use (Temeles 1986;Shine 1989;Butler et al 2000;Pearson et al 2002).…”