Nup96-Dependent Hybrid Lethality Occurs in a Subset of Species From the simulans Clade of Drosophila

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Abstract
The cross of Drosophila melanogaster females to D. simulans males typically produces lethal F1 hybrid males. F1 male lethality is suppressed when the D. simulans Lhr1 hybrid rescue strain is used. Viability of these F1 males carrying Lhr1 is in turn substantially reduced when the hybrids are heterozygous for some mutant alleles of the D. melanogaster Nup96 gene. I show here that similar patterns of Nup96-dependent lethality occur when other hybrid rescue mutations are used to create F1 males, demonstrating that Nup96 does not reduce hybrid viability by suppressing the Lhr1 rescue effect. The penetrance of this Nup96-dependent lethality does not correlate with the penetrance of the F1 hybrid rescue, arguing that these two phenomena reflect genetically independent processes. D. simulans, together with two additional sister species, forms a clade that speciated after the divergence of their common ancestor from D. melanogaster. I report here that Nup96− reduces F1 viability in D. melanogaster hybrids with one of these sister species, D. sechellia, but not with the other, D. mauritiana. These results suggest that Nup96-dependent lethality evolved after the speciation of D. melanogaster from the common ancestor of the simulans clade and is caused by an interaction among Nup96, unknown gene(s) on the D. melanogaster X chromosome, and unknown autosomal gene(s), at least some of which have diverged in D. simulans and D. sechellia but not in D. mauritiana. The genetic properties of Nup96 are also discussed relative to other hybrid lethal genes.