Shared selective pressure and local genomic landscape lead to repeatable patterns of genomic divergence in sunflowers

The repeated evolution of traits in organisms facing similar environmental conditions is considered to be fundamental evidence for the role of natural selection in moulding phenotypes. Yet, aside from case studies of parallel evolution and its genetic basis, the repeatability of evolution at the level of the whole genome remains poorly characterized. Here, through the use of transcriptome sequencing, we examined genomic divergence for three pairs of sister species of sunflowers. Two of the pairs (Helianthus petiolaris – H. debilis and H. annuus – H. argophyllus) have diverged along a similar latitudinal gradient and presumably experienced similar selective pressure. In contrast, a third species pair (H. exilis – H. bolanderi) diverged along a longitudinal gradient. Analyses of divergence, as measured in terms of FST, indicated little repeatability across the three pairs of species for individual genetic markers (SNPs), modest repeatability at the level of individual genes and the highes...