Male-Male Competition

by

Christine W. Miller, Ummat S. Somjee

• LAST REVIEWED: 16 March 2022
• LAST MODIFIED: 13 January 2014
• DOI: 10.1093/obo/9780199941728-0042

Introduction

Sexual selection is among the most powerful of all evolutionary forces. It occurs when one sex competes for fertilization of the gametes of another sex. Sexual selection can be divided into two major forms: intrasexual selection and intersexual selection. Intrasexual selection occurs when members of one sex compete among each other for access to potential mates. Male–male competition is the most common form of intrasexual selection. Intersexual selection, or Oxford Bibliographies article Mate Choice (see the article by Kokko and Jennions). Most species, males compete for access to females, and females are the choosier sex. The difference between males and females rests on the factors that limit reproductive success for each sex. The reproductive success of individual males increases with the number of mates. Thus, males often achieve greater reproductive success by competing with other males to access as many females as possible. Females invest more in each individual offspring and thus cannot produce as many offspring as males. It therefore benefits females to be careful in their choice of mates. When roles are reversed and males invest relatively more in caring for offspring than do females, females often become the competing sex, and males become the choosier sex. Some examples of sex-role–reversed species are jacana birds, seahorses, and giant waterbugs. In monogamous species, both sexes may have intrasexual competitions for mates and be highly choosy. Importantly, the mechanisms of sexual selection do not operate in isolation; thus, it is important to consider both male–male competition and mate choice as well as their post-copulatory equivalents, sperm competition, and cryptic female choice.

General Overviews

Sexual selection, including male–male competition, has been a popular topic among the general public and those researching behavior and evolution. Darwin 1871 provides the genesis of sexual selection theory, explaining the evolution of many beautiful and elaborate traits, including the fan of peacocks and the horns of rhinoceros beetles. Andersson 1994 presents one of the most extensive and authoritative reviews of sexual selection. He emphasizes the importance of male–male competition and mate choice and provides numerous examples. Miller 2013 provides a concise and accessible review of the topic. Shuster and Wade 2003 presents a solid theoretical foundation for the field and illustrates why sexual selection is one of the fastest and strongest of all evolutionary forces. Thornhill and Alcock 1983 offers a classic work providing breadth, detail, and fascinating examples of sexual selection in insects that should be of interest to anyone intrigued by animal behavior.

• Andersson, M. 1994. Sexual selection. Princeton, NJ: Princeton Univ. Press.

  This outstanding book reviews theoretical and empirical advances in the very active field of sexual selection. It will be useful to anyone from undergraduate students to researchers in behavioral ecology and evolutionary biology.

• Darwin, C. R. 1871. The descent of man and selection in relation to sex. London: John Murray.

  Focuses on the evolution of humans as well as sexual selection; published after On the Origin of Species, one of history’s most influential books. Here, Darwin develops the theory of sexual selection, positing that many of the most striking morphological and behavioral traits of animals have arisen as a result of competition for mates through seductive displays and male–male combat.

• Miller, C. W. 2013. Sexual selection: Male–male competition. In The Princeton guide to evolution. Edited by J. Losos, 641–646. Princeton, NJ: Princeton Univ. Press.

  A brief and accessible review of male–male competition. Touches on topics including weapon evolution, alternative mating strategies, sperm competition, male–male competition in plants, and the importance of considering the context of male–male competition.

• Shuster, S. M., and M. J. Wade. 2003. Mating systems and strategies. Princeton, NJ: Princeton Univ. Press.

  This book provides a unified quantitative and conceptual framework for the evolution of reproductive strategies and is grounded in evolutionary genetics. It links sexual selection with ecology and life history. A focus of this book is the evolution of alternative mating strategies, and the authors provide direction on how these strategies can be used to measure sexual selection.

• Thornhill, R., and J. Alcock. 1983. The evolution of insect mating systems. Cambridge, MA: Harvard Univ. Press.

  A classic work that provides an excellent collection of invertebrate examples organized into a logical theoretical framework. It highlights the importance of insects for advancing understanding of sexual selection. This book provides one of the more important contributions to the fields of behavioral ecology and evolutionary biology.