The origin of chromosomal inversions as a source of segmental duplications in the Sophophora subgenus of Drosophila.

Chromosomal inversions can contribute to the adaptation of organisms to their environment by capturing particular advantageous allelic combinations of a set of genes included in the inverted fragment and also by advantageous functional changes due to the inversion process itself that might affect not only the expression of flanking genes but also their dose and structure. Of the two mechanisms originating inversions -ectopic recombination, and staggered double-strand breaks and subsequent repair- only the latter confers the inversion the potential to have dosage effects and/or to generate advantageous chimeric genes. In Drosophila subobscura, there is ample evidence for the adaptive character of its chromosomal polymorphism, with an important contribution of some warm-climate arrangements such as E1+2+9+12. Here, we have characterized the breakpoints of inversion E12 and established that it originated through the staggered-break mechanism like four of the five inversions of D. subobscura previously studied. This mechanism that also predominates in the D. melanogaster lineage might be prevalent in the Sophophora subgenus and contribute to the adaptive character of the polymorphic and fixed inversions of its species. Finally, we have shown that the D. subobscura inversion breakpoint regions have generally been disrupted by additional structural changes occurred at different time scales.