The impact of shared ancestral variation on hybrid male lethality--a 16 codon indel in the Drosophila simulans Lhr gene.

The Lethal hybrid rescue (Lhr) gene causes hybrid male lethality in crosses between Drosophila simulans and D. melanogaster. Lhr(2) is a D. simulans allele,which rescues hybrid males. It has been recently proposed that a 16 codon insertion, which distinguishes the D. melanogaster and the canonical D. simulansallele, and is lacking in Lhr(2), may be responsible for the functional divergence of D. melanogaster and D. simulans Lhr alleles. Here, we show that the Lhr(2) allele lacking the insertion represents an ancestral polymorphism segregating at a moderate frequency in D. simulans. Crosses of D. melanogaster females to males from two D. simulans strains carrying this deletion showed a severe deficiency of viable hybrid males. Our results suggest that the absence of this insertion alone is not sufficient to explain functional differences betweenD. melanogaster and D. simulans Lhr alleles.