Two Dobzhansky-Muller genes interact to cause hybrid lethality in Drosophila

The Dobzhansky-Muller model proposes that hybrid incompatibilities are caused by the interaction between genes that have functionally diverged in the respective hybridizing species. Here, we show that Lethal hybrid rescue ( Lhr ) has functionally diverged in Drosophila simulans and interacts with Hybrid male rescue ( Hmr ), which has functionally diverged in D. melanogaster , to cause lethality in F1 hybrid males. LHR localizes to heterochromatic regions of the genome and has diverged extensively in sequence between these species in a manner consistent with positive selection. Rapidly evolving heterochromatic DNA sequences may be driving the evolution of this incompatibility gene.