| Description |
The chromosomal inversions of D. persimilis and D. pseudoobscura have deeply influenced our understanding of the evolutionary forces that shape natural variation, speciation, and selfish chromosome dynamics. Here, we perform a comprehensive reconstruction of the evolutionary histories of the chromosomal inversions in these species and provide a solution to the puzzling origins of the selfish Sex-Ratio chromosome in D. persimilis. We show that this Sex-Ratio chromosome directly descends from an ancestrally-arranged chromosome, suggesting that unsuppressed selfish chromosomes may remain polymorphic within populations for long periods of time. We further show that all fixed inversions between D. persimilis and D. pseudoobscura were segregating in the ancestral population long before speciation, and that the genes contributing to reproductive barriers must have evolved within them afterwards. We propose a new model for the role of chromosomal inversions in speciation and suggest that higher levels of divergence and an over-abundance of hybrid incompatibilities are emergent properties of ancestrally segregating inversions. Our findings force a reconsideration of the role of chromosomal inversions in speciation, not as a protector of existing hybrid incompatibility alleles, but as fertile ground for their formation. |
