On the logic of Fisherian sexual selection

Abstract

In Fisher's model of sexual selection, a female preference for a male trait spreads together with the trait because their genetic bases become correlated. This can be interpreted as a 'greenbeard' system: a preference gene, by inducing a female to mate with a trait-bearing male, favors itself because the male is disproportionately likely also to carry the preference gene. Here, we use this logic to argue that Fisherian sexual selection in diploids proceeds via two channels, corresponding to two reasons that trait-bearing males disproportionately carry preference genes: (i) trait-bearing males are disproportionately the product of matings between preference-bearing mothers and trait-bearing fathers, and thus trait and preference genes are correlated 'in trans'; (ii) trait and preference genes come into gametic phase disequilibrium, and thus are correlated 'in cis'. Gametic phase disequilibrium is generated by three distinct mechanisms: a 'recombination mechanism', a 'dominance mechanism', and a 'sexual admixture mechanism'. The trans channel does not operate when sexual selection is restricted to the haploid phase, and therefore represents a fundamental difference between haploid and diploid models of sexual selection. We use simulation experiments to artificially eliminate the cis channel, and show that a preference gene can spread in its absence in the diploid model, but not in the haploid model. We further show that the cis and trans channels contribute equally to the spread of the preference when recombination between the preference and trait loci is free, but that the trans channel becomes substantially more important when linkage is tight.

When do opposites attract? A model uncovering the evolution of disassortative mating

“…Once mate preferences are established in the population, they generate sexual selection on the traits exhibited by individuals during courtship, that may drive the evolution of extravagant traits in males, following a Fisherian runaway (Fisher, 1930; Gomulkiewicz and Hastings, 1990; Greenspoon and Otto, 2009; Kirkpatrick, 1982; Lande, 1981; O’Donald, 1980b; Otto, 1991; Veller et al, 2020). The evolution of mate preferences thus involves complex evolutionary processes where preferences co-evolve with the cues displayed by the chosen individuals.…”

Digest: Differentiating Fisherian sexual selection dynamics between haploids and diploids*

“…In this issue, Veller et al. (2020) studied a diploid version of Kirkpatrick's (1982) canonical two‐locus model of Fisherian sexual selection to investigate the fundamental differences between haploid and diploid models and identify important parameters that can influence diploid sexual selection.…”

“…Allele T is costly but preferred by females carrying allele P. At the beginning of each non-overlapping generation, individuals that survive viability selection mate preferentially according to their genotype. Veller et al (2020) show that cis-linkage disequilibrium (c-LD) between the P and T alleles is generated by three mechanisms: recombination, dominance, and syngamic admixture. The last two mechanisms, dominance and syngamic admixture, have not been previously investigated.…”

“…The diploid model that Veller et al. (2020) studied is a two‐locus model consisting of a population with two autosomal loci, where T is the male‐specific trait locus and P is the female preference locus. Allele T is costly but preferred by females carrying allele P .…”

“…Veller et al. (2020) show that cis ‐linkage disequilibrium (c‐LD) between the P and T alleles is generated by three mechanisms: recombination, dominance, and syngamic admixture. The last two mechanisms, dominance and syngamic admixture, have not been previously investigated.…”