Functional conservation of the Drosophila hybrid incompatibility gene Lhr

Background: Hybrid incompatibilities such as sterility and lethality are commonly modeled as being caused by interactions between two genes, each of which has diverged separately in one of the hybridizing lineages. The gene Lethal hybrid rescue (Lhr) encodes a rapidly evolving heterochromatin protein that causes lethality of hybrid males in crosses between Drosophila melanogaster females and D. simulans males. Previous genetic analyses showed that hybrid lethality is caused by D. simulans Lhr but not by D. melanogaster Lhr, confirming a critical prediction of asymmetry in the evolution of a hybrid incompatibility gene. Results: Here we have examined the functional properties of Lhr orthologs from multiple Drosophila species, including interactions with other heterochromatin proteins, localization to heterochromatin, and ability to complement hybrid rescue in D. melanogaster/D. simulans hybrids. We find that these properties are conserved among most Lhr orthologs, including Lhr from D. melanogaster, D. simulans and the outgroup species D. yakuba. Conclusions: We conclude that evolution of the hybrid lethality properties of Lhr between D. melanogaster and D. simulans did not involve extensive loss or gain of functions associated with protein interactions or localization to heterochromatin.