Hybrid zone dynamics under weak Haldane's rule

TL;DR

This paper investigates how weak hybrid incompatibilities under Haldane's rule influence gene flow and allele distribution in hybrid zones, revealing that even minor incompatibilities can significantly impact speciation processes.

Contribution

It provides a mechanistic model showing how weak heterogametic hybrid incompatibilities can create barriers to gene flow and affect clinal structures in hybrid zones.

Findings

Weak hybrid incompatibilities can reduce gene flow.

Differential gene flow is amplified by density-dependent regulation.

Allele clines can become discordant due to incompatibilities.

Abstract

The ability of genetic isolation to block gene flow plays a key role in the speciation of sexually reproducing organisms. This paper analyses the hybrid zone dynamics affected by "weak" Haldane's rule, namely the incomplete hybrids inferiority (sterility/inviability) against the heterogametic (XY or ZW) sex caused by a Dobzhansky-Muller incompatibility. Different strengths of incompatibility, dispersal and density-dependent regulation are considered; and the gene flow and clinal structures of allele frequencies in the presence of short-range dispersal (the stepping-stone model) are examined. I show that a weak heterogametic hybrid incompatibility could constitute a substantial barrier that could reduce gene flow and result in non-coincident and discordant clines of alleles. It is found that the differential gene flow is more pronounced under a stronger density-dependent regulation. This study provides a mechanistic explanation for how an adaptive mutation, which may only have a marginal fitness effect, could set a gene up as an evolutionary hot-spot.