Sexual Conflict

Abstract

Although females and males share a common interest in successful reproduction, the sexes often maximise their reproductive success (fitness) in mutually incompatible ways. Two basic forms of sexual conflict are recognised: Interlocus sexual conflict reflects a conflict of interest over the outcome of an interaction between sexes (e.g. to mate or not?), with some genetic loci evolving to enhance male fitness at females’ expense and other loci evolving to promote female fitness by mitigating male‐imposed harm. This conflict drives the evolution of sexually antagonistic male strategies such as coercive behaviours and morphologies, toxic ejaculates and infanticide, and female counter‐adaptations that confer resistance to such strategies. Intralocus sexual conflict reflects divergent selection on a shared trait whose expression is influenced by the same loci in both sexes, such that selection on one sex can displace the other sex from its phenotypic optimum. It selects for genomic adaptations that permit the evolution of sexual dimorphism.

Key Concepts:

  • Sexual conflict arises because strategies that maximise the fitness of one sex can reduce the fitness of the other sex.

  • Two basic forms of sexual conflict are recognised: interlocus (between genetic loci) and intralocus (within a genetic locus).

  • Interlocus sexual conflict is a conflict of interest over the outcome of some interaction (e.g. to mate or not?), mediated by different genetic loci in each sex.

  • Sexual conflict can lead to sexually antagonistic coevolution and sexual ‘arms races’, whereby adaptations that benefit males at females’ expense select for counter‐adaptations in females that mitigate male‐imposed harm.

  • Interlocus sexual conflict is manifested in a variety of traits that increase male reproductive success but harm females in the process, including behavioural harassment and coercion, morphological armaments such as genital spines and chemical manipulation via ejaculate components or pheromones.

  • Intralocus sexual conflict is a conflict of interest over the expression of a shared trait that is subject to sex‐specific patterns of selection but influenced by the same genetic loci in both sexes.

  • Intralocus sexual conflict selects for modifications to the genetic basis of trait expression that allow each sex to evolve towards its phenotypic optimum, resulting in sexual dimorphism.

  • Intralocus sexual conflict challenges the ‘good genes’ model of sexual selection because females that mate with high‐quality males may produce low‐quality daughters.

  • Sexual conflict may increase the costs of sexual reproduction, reduce mean fitness in populations and (in theory) even promote population extinction.

  • The study of sexual conflict has become one of the most important and dynamic areas in evolutionary biology.

Keywords: sexual selection; sexually antagonistic coevolution; sexual arms race; interlocus sexual conflict; intralocus sexual conflict; signaller–receiver coevolution; reproduction; mate choice; mating system; Red Queen

Figure 1.

A pair of Australian Soldier Beetles (family Cantharidae) engaged in copulation: the striking sexual dimorphism in body size reflects divergent reproductive strategies that generate sex‐specific selection on a host of morphological, behavioural, physiological and life‐history traits and engender sexual conflict. Copyright © 2010 R Bonduriansky.

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Bonduriansky, Russell(Sep 2010) Sexual Conflict. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003669.pub2]