# Looking for the right mate in diploid species: how dominance relationships affect population differentiation in sexual trait?

## TL;DR

This study investigates how dominance relationships in diploid species influence population differentiation driven by natural and sexual selection, revealing that heterozygote behavior significantly impacts divergence outcomes.

## Contribution

The paper introduces a diploid model analyzing how dominance affects population differentiation, emphasizing the importance of heterozygote behavior in speciation processes.

## Key findings

- Differentiation is limited in diploids compared to haploids.
- Co-dominance requires low migration for differentiation.
- Strict dominance reduces dependence on migration for differentiation.

## Abstract

Divergence between populations for a given trait can be driven by natural or sexual selection, interacting with migration behaviour. Mating preference for different phenotypes can lead to the emergence and persistence of differentiated populations. Dominance between alleles encoding for divergent phenotypes can interfere in such processes. Using a diploid model of trait determining both mating success and migration rate, we explored differentiation between two connected populations, assuming either co-dominance or strict dominance between alleles. The model assumes that individuals prefer mating with partners displaying the same phenotype and therefore tend to move to the other population when their own phenotype is rare. We show that the emergence of differentiated populations in this diploid model is limited as compared to results obtained with the same model assuming haploidy. When assuming co-dominance, differentiation arises only when migration is limited as compared to preference. Such differentiation is less dependent on migration when assuming strict dominance between haplotypes. Dominant alleles frequently invade populations because their phenotype is more frequently expressed, resulting in higher mating success and rapid decrease in migration. However, depending on the initial distribution of alleles, this advantage associated with dominance (i.e. Haldane's sieve) may lead to fixation of the dominant allele throughout both populations. Depending on the initial distribution of heterozygotes, persistence of polymorphisms within populations can also occur because heterozygotes displaying the predominant phenotype benefit from mating preferences. Altogether, our results highlight that heterozygotes' behaviour has a strong impact on population differentiation and stress out the need of diploid models of differentiation and speciation driven by natural and sexual selection.