Drosophila melanogaster and D. simulans rescue strains produce fit offspring, despite divergent centromere-specific histone alleles

Abstract

The interaction between rapidly evolving centromere sequences and conserved kinetochore machinery appears to be mediated by centromere-binding proteins. A recent theory proposes that the independent evolution of centromerebinding proteins in isolated populations may be a universal cause of speciation among eukaryotes. In Drosophila the centromere-specific histone, Cid (centromere identifier), shows extensive sequence divergence between D. melanogaster and the D. simulans clade, indicating that centromere machinery incompatibilities may indeed be involved in reproductive isolation and speciation. However, it is presently unclear whether the adaptive evolution of Cid was a cause of the divergence between these species, or merely a product of postspeciation adaptation in the separate lineages. Furthermore, the extent to which divergent centromere identifier proteins provide a barrier to reproduction remains unknown. Interestingly, a small number of rescue lines from both D. melanogaster and D. simulans can restore hybrid fitness. Through comparisons of cid sequence between nonrescue and rescue strains, we show that cid is not involved in restoring hybrid viability or female fertility. Further, we demonstrate that divergent cid alleles are not sufficient to cause inviability or female sterility in hybrid crosses. Our data do not dispute the rapid divergence of cid or the coevolution of centromeric components in Drosophila; however, they do suggest that cid underwent adaptive evolution after D. melanogaster and D. simulans diverged and, consequently, is not a speciation gene.

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“…Centromere drive provides a mechanism for the tendency of karyotypes to be either mostly metacentric or mostly acrocentric [59] and for the karyotype-specific accumulation of selfish B chromosomes in mammals [60]. Our finding that CENP-Cs, like CenH3s, evolve adaptively addresses a perceived shortcoming of the centromere drive model for post-zygotic reproductive isolation: mutations that rescued hybrid sterility did not map to the Drosophila CenH3 gene [61,62]. The fact that CenH3 is not the only adaptively evolving centromere protein indicates that there are multiple candidate drive suppressors that might rescue hybrid sterility when in a mutant form.…”

Natural Variation of the Amino-Terminal Glutamine-Rich Domain in Drosophila Argonaute2 Is Not Associated with Developmental Defects

“…D. melanogaster strains Tai255.1 , w-14 melbourne and Oregon R** as well as D. simulans strains Oxnard , Tsimbazaza , vermilion , maz1 , maz6 and C167.4 were a gift from H. Hollocher. These strains are described in Sainz et al [53]. Additional strains were obtained from the Tucson Drosophila Stock Center: three D. simulans strains ( sim1  =  #14021-0251.48, sim2  =  #14021-0251.047, sim3  =  #14021-0251.004), one D. mauritiana strain (#14021-0241.46) and two D. sechellia strains (#14021-0248.08, #14021-0248.25).…”

Eggshells of Drosophila melanogaster and D. simulans: Ultrastructure, Measurement and Analyses

“…When D. melanogaster 'rescue' strain, In(1) AB, was used to generate the viable and fertile F 1 [In(1) AB, w/X sim] females and these females were further backcrossed with In(1)AB, w males, a small number of eggs were generated at 18-25°C ( Table 2). The eggs of F 1 hybrid females were [95 % fertile at 25°C [41,42]. The ultrastructure of the chorion of hybrid eggs provide evidence that, as it was noted above, both paternal genomes are involved in regulating the chorionic patterns.…”