Genomic Signatures of Sexual Conflict

Abstract

Sexual conflict is a specific class of intergenomic conflict that describes the reciprocal sex-specific fitness costs generated by antagonistic reproductive interactions. The potential for sexual conflict is an inherent property of having a shared genome between the sexes and, therefore, is an extreme form of an environment-dependent fitness effect. In this way, many of the predictions from environment-dependent selection can be used to formulate expected patterns of genome evolution under sexual conflict. However, the pleiotropic and transmission constraints inherent to having alleles move across sex-specific backgrounds from generation to generation further modulate the anticipated signatures of selection. We outline methods for detecting candidate sexual conflict loci both across and within populations. Additionally, we consider the ability of genome scans to identify sexually antagonistic loci by modeling allele frequency changes within males and females due to a single generation of selection. In particular, we highlight the need to integrate genotype, phenotype, and functional information to truly distinguish sexual conflict from other forms of sexual differentiation.

Keywords: genome evolution; interlocus sexual conflict; intersexual genetic covariance; intralocus sexual conflict; linkage disequilibrium; pleiotropy.

Figure 1.

The effects of sexual conflict on polymorphism and linkage and methods for their detection. Interlocus and intralocus sexual conflict represent specific instances of broader categories of selection. Trajectories of conflict-associated alleles are shown through time, with unique alleles shown in shades of gray. Representative shifts in the SFS surrounding conflict alleles are shown below their respective trajectories. Solid lines represent the neutral expectation based on Watterson (1975). Effects on linkage and methods for detection are summarized below and in the text.

Figure 2.

The change in the male-beneficial allele frequency with additive beneficial and conflict allele effects (h₁ = h₂ = 0.5) after a single generation of sexually antagonistic selection, where the cost of selection is equal between the sexes (s_m = s_f = s). (A) The difference between male and female allele frequencies (∆q) as a function of selection for different initial values of q. (B) Male-female F_ST as a function of selection for different values of q. For both response measures, the change in allele frequency increases as the cost of selection increases. The maximum change in allele frequency is seen when the male- and female-beneficial alleles start at the same frequency (q = 0.5).

Figure 3.

The change in the male-beneficial allele frequency due to a single generation of sexually antagonistic selection is dependent on the dominance relationships between the sexes. When there is conflict allele (h₁ = h₂ = 1) or beneficial allele (h₁ = h₂ = 0) dominance in both sexes, the difference in allele frequency is maximized when the male and female-beneficial alleles start at the same frequency (q = 0.5). Additionally, there is a diminishing response to selection, such that the difference in allele frequency between the sexes forms a concave surface. Sex-specific beneficial allele dominance changes the shape and magnitude of the selection response curve. For example, when the female-beneficial allele is dominant (h₁ = 1, h₂ = 0), the response surface is shifted and stretched. Here the cost of selection is equal between the sexes (s_m = s_f = 0.1).