Genotype-by-environment interaction and the Dobzhansky-Muller model of postzygotic isolation

The Dobzhansky-Muller (D-M) model of reproductive isolation (RI) posits tha t hybrid sterility and inviability result from negative epistatic interacti ons between alleles at a minimum of two genes. This standard model makes se veral implicit assumptions, including a lack of environmental effects and g enotype-by-environment interactions (GEI) involving hybrid sterility and hy brid inviability loci. Here we relax this assumption of the standard D-M mo del. By doing so, several patterns of the genetic architecture of RI change . First, a novel single-locus model of postzygotic RI emerges. Several indi rect lines of evidence are discussed in support of the model, but we conclu de that this new single-locus model is currently no more supported than pre vious ones. Second, when multilocus D-M models incorporating GEI are consid ered, we find that the number of potential negative epistatic interactions increases dramatically over the number predicted by the standard D-M model, even when only the most simple case of two-allele interactions are conside red. Third, these multilocus models suggest that some previous generalizati ons about the evolutionary genetics of postzygotic RI may not necessarily h old. Our findings also suggest that the evolution of postzygotic RI may be more likely when the expression of traits driving speciation is affected by the environment, since there appears to be a greater spectrum of potential hybrid incompatibilities under the D-M model incorporating GEI.