Mate-pair data to detect structural variants in Timema cristinae

Theory predicts that structural genomic variants such as inversions can promote adaptive diversification and speciation. Despite increasing empirical evidence that adaptive divergence can be triggered by one or a few large inversions, the degree to which widespread genomic regions under divergent selection are associated with structural variants remains unclear. Here we test for an association between structural variants and genomic regions that underlie parallel host-plant associated ecotype formation in Timema cristinae stick insects. Using mate-pair re- sequencing of 20 new whole genomes we find that modest-sized structural variants such as inversions, deletions, and duplications are widespread across the genome, being retained as standing variation within and among populations. Using 160 previously published, standard- orientation whole genome sequences we find little to no evidence that the DNA sequences within inversions exhibit accentuated differentiation between ecotypes. In contrast, a formerly described large region of reduced recombination that harbors genes controlling color-pattern exhibits evidence for accentuated differentiation between ecotypes, which is consistent with differences in the frequency of color-pattern morphs between host-associated ecotypes. Our results suggest that some types of structural variants (e.g., large inversions) are more likely to underlie adaptive divergence than others, and that structural variants are not required for subtle yet genome-wide genetic differentiation with gene flow.