Abstract
Genetic incompatibilities are supposed to play an important role in speciation. A general (theoretical) problem is to explain the persistence of genetic diversity after secondary contact. Previous theoretical work has pointed out that Dobzhansky-Muller incompatibilities (DMI) are not stable in the face of migration unless local selection acts on the alleles involved in incompatibility. With local selection, genetic variability exists up to a critical migration rate but is lost when migration exceeds this threshold value. Here, we investigate the effect of intracellular bacteria Wolbachia on the stability of hybrid zones formed after the Dobzhansky Muller model. Wolbachia are known to cause a cytoplasmic incompatibility (CI) within and between species. Incorporating intracellular bacteria Wolbachia can lead to a significant increase of critical migration rates and maintenance of divergence, primarily because Wolbachia-induced incompatibility acts to reduce frequencies of F1 hybrids. Wolbachia infect up to two-thirds of all insect species and it is therefore likely that CI co-occurs with DMI in nature. The results indicate that both isolating mechanisms strengthen each other and under some circumstances act synergistically. Thus they can drive speciation processes more forcefully than either when acting alone.
Highlights
The Dobzhansky-Muller model has been used to study speciation in a variety of contexts [1,2,3,4]
Before elaborating on the dynamics of this extended model, we first analyze the Dobzhansky-Muller model in the absence of cytoplasmic incompatibility (CI)-bacteria and examine the conditions under which genetic diversity is maintained
Whether resident alleles can coexist with migrant alleles Am and Bm or Ai and Bi become extinct depends on the migration rate (m), the selection coefficient (s), and on the degree and architecture of reproductive isolation
Summary
The Dobzhansky-Muller model has been used to study speciation in a variety of contexts [1,2,3,4]. In the present study we investigate the effects of Wolbachia on the stability of Dobzhansky-Muller incompatibilities in a diploid genetic system, allowing for variable levels of dominance. These results suggest that a high degree of reproductive isolation as well as local positive selection on incompatibility alleles lead to a higher stability of hybrid zones and that the stabilizing effect of Wolbachia increases with increasing strength of CI.
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