Sexual Selection and Speciation

by

Janette W. Boughman, Jason Keagy, Emily Weigel

• LAST REVIEWED: 05 May 2023
• LAST MODIFIED: 28 February 2017
• DOI: 10.1093/obo/9780199941728-0086

Introduction

The widespread observation that for many closely related taxa, sexual traits differ more markedly than other traits, underpins the hypothesis that sexual selection is often a major cause of speciation. Quite a few empirical studies support this hypothesis, by demonstrating that the traits that are targets of sexual selection within species are also critical to premating reproductive isolation (sexual isolation) between species. Despite these convincing studies, the hypothesis remains controversial. Fueling the controversy, results from comparative analyses are equivocal, with some studies providing support, others failing to find any relationship between sexual selection and speciation metrics, and others actually suggesting that sexual selection is more likely to cause extinction than speciation. Theoretical work is likewise mixed. Because of these mixed results, we lack a general answer to this question: Does sexual selection cause speciation?

General Overviews of Speciation

Several books have done an excellent job in reviewing the recent progress and potential for future studies in speciation. Those works included in this section touch on the role of sexual selection, but no book yet addresses it as a primary focus. Coyne and Orr 2004 is the most general. Schluter 2000, which focuses on adaptive radiation and the role of ecology and selection, has influenced the burgeoning field of ecological speciation, which Nosil 2012 reviews. Although Price 2008 focuses on birds, the book also raises many generalities of importance to other taxa. Gavrilets 2004 presents a novel and influential theoretical framework that has brought heightened attention to using fitness landscapes to understand diversification.

• Coyne, J. A., and H. A. Orr. 2004. Speciation. Sunderland, MA: Sinauer.

  This book should be considered “canon” for anyone studying speciation. It reviews speciation through many mechanisms (not just sexual selection), and provides evidence across a wide array of taxa for the generalities of the speciation process. It is extremely valuable in consolidating and making clear the patterns and patches of knowledge in speciation research, and serves as an excellent guide, particularly for those beginning to study speciation.

• Gavrilets, S. 2004. Fitness landscapes and the origin of species. Princeton, NJ: Princeton Univ. Press.

  Gavrilets’s book provides important theoretical insight and synthesizes mathematical models of speciation, including those that explore sympatric speciation and sexual selection. Gavrilets develops a novel analytical approach to the highly dimensional nature of selection. His “holey landscape” framework recognizes that many genotypic and phenotypic combinations will have high fitness, flattening the fitness landscape and facilitating evolution. However, some combinations have low fitness, falling into fitness “holes.”

• Nosil, P. 2012. Ecological speciation. Oxford: Oxford Univ. Press.

  DOI: 10.1093/acprof:osobl/9780199587100.001.0001

  This book nicely reviews the available evidence on the ecological processes that form new species, and tackles several controversial topics. The focus is on natural selection, but there is some treatment of how assortative mating can evolve through sexual selection as well. Through examining findings from manipulative experiments, genomics, and theoretical literature on ecological speciation, this book synthesizes our current understanding and offers predictions for future research directions. Particularly useful are ideas for better integration of empirical and theoretical work.

• Price, T. D. 2008. Speciation in birds. Greenwood Village, CO: Roberts.

  Price’s approach is refreshing, as it advocates for integrating ecology, behavior, and genetics in understanding speciation. Although this book deals only with birds, its synthesis and insights are important for understanding general patterns of speciation, and the role for sexual and natural selection. Price embraces the social selection perspective of M. J. West-Eberhard (see West-Eberhard 1983, cited in the Early History of Sexual Selection and Speciation), and discusses how song learning affects the evolution of premating isolation.

• Schluter, D. 2000. The ecology of adaptive radiation. Oxford: Oxford Univ. Press.

  This book focuses on the ecological causes of diversification due to divergent natural selection among environments, and also considers situations in which sexual selection depends on environment (such as sensory drive). It systematically considers the causes of adaptive radiation due to ecological differences and provides many detailed natural examples, pointing out challenges, the state of current evidence, and unexplored theoretical territory. Its lucid presentation makes this an excellent entry to speciation research.