Evolutionary consequences of assortativeness in haploid genotypes

TL;DR

This paper investigates how non-random mating based on incompatibility at two loci influences allele frequencies in haploid populations, leading to reduced diversity and specific equilibrium states, with implications for understanding speciation.

Contribution

It introduces a model of haploid evolution with incompatibility, revealing how it causes allele loss, correlation between loci, and provides a geometric and dynamical analysis of equilibrium states.

Findings

One allele disappears, reducing diversity.

Certain allele combinations remain constant during evolution.

Equilibrium depends only on initial allele frequencies.

Abstract

We study the evolution of allele frequencies in a large population where random mating is violated in a particular way that is related to recent works on speciation. Specifically, we consider non-random encounters in haploid organisms described by biallelic genes at two loci and assume that individuals whose alleles differ at both loci are incompatible. We show that evolution under these conditions leads to the disappearance of one of the alleles and substantially reduces the diversity of the population. The allele that disappears, and the other allele frequencies at equilibrium, depend only on their initial values, and so does the time to equilibration. However, certain combinations of allele frequencies remain constant during the process, revealing the emergence of strong correlation between the two loci promoted by the epistatic mechanism of incompatibility. We determine the geometrical structure of the haplotype frequency space and solve the dynamical equations, obtaining a simple rule to determine equilibrium solution from the initial conditions. We show that our results are equivalent to selection against double heterozigotes for a population of diploid individuals and discuss the relevance of our findings to speciation.