Genotype-by-Environment Interactions and Sexual Selection

John Hunt, David J. Hosken, John Hunt, David J. Hosken

• Publisher: Wiley-Blackwell
• Year: 2014
• Print ISBN: 9780470671795
• eBook ISBN: 9781118912621
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Evolution
• Index: Biological Sciences

Sexual selection is recognized as being responsible for some of the most extravagant morphologies and behaviors in the natural world, as well as a driver of some of the most rapid evolution. While Charles Darwin's theory is now a fundamental component of modern evolutionary biology, the impact of genotype-by-environment interactions on sexual selection has thus far received little attention.

This book represents the first comprehensive analysis of the role genotype-by-environment interactions play in sexual selection and the potential implications that they have for the evolutionary process. The Editors have identified 13 topics that currently define the field and shed light on the impacts of these interactions on sexual selection. This includes key topics, such as resolving the lek paradox and how genotype-by-environmental interactions can compromise the honesty of sexual signals. The volume also outlines key questions that remain unanswered and provides a comprehensive guide to analyzing genotype-by-environment interactions.

The mix of theory, empirical studies, and practical instructions from world leading experts make this book a particularly potent and definitive guide on the topic. It will be of interest to evolutionary biologists, spanning from genomicists to behaviorists.

"This is a very timely book, covering a topic that should change the way we think about sexual selection. The contributors are all leaders and the topics should provide guidance to many PhD projects in the years to come. GEI is increasingly shown to be important, and it seems likely that it is critical in species where sexual selection is operating. This book is likely to help revitalize the study of sexual selection." Professor Allen Moore, The University of Georgia

"GEIs fascinate evolutionary biologists, but the unique consequences for sexually selected traits have been neglected - until now. This multi-authored book comprehensively explains key theoretical concepts, handles practical 'how to' issues and uses classic case studies to illustrate the value of studying GEIs. It is a must read for everyone interested in sexual selection." Professor Michael Jennions, The Australian National University

Part I

Introduction and Theoretical Concepts

Chapter 1
Genotype-by-Environment Interactions and Sexual Selection: Female Choice in a Complex World

Michael J. Wade

Department of Biology, Indiana University, USA

1.1 Introduction

“When the males and females of any animal have the same general habits of life, but differ in structure, colour, or ornament, such differences have been mainly caused by sexual selection” (Darwin, 1859, p. 89). Female choice of mates and male–male reproductive competition were the two mechanisms causing sexual selection proposed by Darwin. Darwin proposed male–male reproductive competition as an explanation for the evolution of male-limited structures, like antlers, horns, fangs, and claws, which function in reproductive combat among males. But, he proposed female mate choice as the explanation for the evolution of exaggerated male traits, which have no apparent function in reproductive competition like plumage, color, and ornamentation. Darwinian sexual selection accounted for two patterns in nature: (1) males and females of the same species differ from one another; and, (2) males of closely related species tend to be much more different from one another in structure and behavior than the females.

In an insightful elaboration of Darwin's theory, Fisher (1930) gave formal expression to the “run-away” process of sexual selection, wherein the existence of a female mating preference by itself favors the evolutionary exaggeration of the favored male trait. When females differ from one another in mate preference and males vary from one another in the preferred trait, then males with the most extreme trait values have more mates as a result of satisfying the mating preferences of more females. Sons of these males inherit the father's more extreme trait value and their daughters inherit their mothers' preferences, making them more selective (Lande, 1981). It is this positive feedback between the female mating preference and the male preferred trait that results in run-away sexual selection, where the male trait mean is dragged off its natural selection optimum through its mating advantage.

Bateman (1948) found empirically that the variance in male relative fitness was greater than that of females owing to the variance among males in mate numbers. Wade (1979; 1995) derived the formal relationship between the variance in male relative fitness and that of females, generalizing Bateman's inference from observations. This finding is important because selecting for a gene in one sex but against it in the other averages to a fairly small change in a gene's frequency (Shuster & Wade, 2003). And, such weak selection is a poor candidate for the selective force behind the large differences in morphology and behavior between males of closely related species. However, when the strength of selection on males is several times that acting on females, sex-limited divergence among closely related species is to be expected.

The modern view of female choice, which emphasizes “good genes” and “sexual conflict,” differs somewhat from that of Fisher and Bateman. In a complex world, one with genotype-by-environment interactions (G × E) and gene-by-gene interactions (G × G or epistasis), it is very difficult for a female to choose her mates in order to obtain “good genes.” With G × E and G × G, a gene's effect on fitness is context-dependent; a gene can be good for fitness in one context but a bad for it in another. Furthermore, recent genomic studies of the determinants of feather quality, an often discussed target of female mate choice in birds, find that the quality of a male's feathers depends more on the genes in his neighbors' genomes than it does on the genes in his own (Biscarini et al., 2010). That is, the social environment of other males contains genes that affect feather quality. Such genetic indirect effects are often represented as G × E_G to emphasize the notion that “the environment contains genes.” And, G × E_G in evolutionary theory behaves somewhat like a hybrid of the concepts G × E and G × G. In the context of female mate choice, it is important to recognize not only that G × E_G plays a role in competitive interactions, including competition for mates, but also why it responds poorly or not at all to individual selection. In this chapter, I will discuss the difficulty in obtaining good genes by female choice in a complex world, where male traits are affect by G × E, G × G and G × E_G. First, however, I want to resurrect the history behind “good genes” theory in order that the arguments in its favor are clear.

1.2 Classical female choice

What do females gain by choosing mates? In their influential paper on female mate choice, Hamilton and Zuk (1982) answered in this way:

Whether mate choice could be based mainly on genetic quality of the potential mate has been a puzzle to evolutionary biologists…females of many species act as if they are choosing males for their genes; thus “good genes” versions of sexual selection have been frequently, albeit tentatively, suggested.

They went further, specifying how a female should select a mate:

The methods used should have much in common with those of a physician checking eligibility for life insuran...

Table of contents

• Cover
• Dedication
• Title Page
• Copyright
• List of Contributors
• Preface
• About the Companion Website
• Part I: Introduction and Theoretical Concepts
• Part II: Practical Issues for Measuring GEIs
• Part III: Empirical Studies on GEIs and Sexual Selection
• Conclusions and Final Thoughts
• Index
• End User License Agreement