| Summary: | While parallel evolution, the repeated evolution of similar traits in related taxa, provides important insights into the mechanisms and constraints underlying evolution, whether parallel traits originate from the same genomic regions is unclear. To investigate the genomic basis of parallel evolution, I examined populations of the band-rumped and Leach’s storm-petrel species complexes (Hydrobates spp). Many colonies of these highly pelagic seabirds contain sympatric populations that independently diverged in breeding season – an example of parallel allochronic divergence. I used low-coverage whole-genome sequences of 115 birds, representing all colonies with allochronic populations. For each colony, I identified genomic outliers differentiating seasonal populations using PCAdapt and windowed FST scans and examined whether the same outliers were detected in multiple colonies – i.e. genetic parallelism. I complemented the outlier analyses with tests of introgression – D and fdM statistics – between colonies to further clarify the likely genomic mechanism underlying allochrony. Despite some shared outliers, genetic parallelism was low among archipelagos. Moreover, evidence of introgression between colonies were generally not consistent with the patterns of seasonal population divergence. However, signals of introgression around outliers for some North Atlantic archipelagos suggest that introgression may have influenced allochronic divergence in those colonies. Combined, these patterns potentially indicate that allochronic divergence in storm-petrels occurred mainly through independent adaptations in each archipelago, with contributions from standing genetic variation and introgression. M.Sc.
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