Journal
EVOLUTION
Volume 62, Issue 5, Pages 1162-1181Publisher
WILEY
DOI: 10.1111/j.1558-5646.2008.00352.x
Keywords
AFLPs; divergent natural selection; herbivorous insects; population divergence; reproductive isolation; speciation genetics
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This study uses a comparative genome scan to evaluate the contributions of host plant related divergent selection to genetic differentiation and ecological speciation in maple- and willow-associated populations of Neochlamisus bebbianae leaf beetles. For each of 15 pairwise population comparisons, we identified outlier loci whose strong differentiation putatively reflects divergent selection. Of 447 AFLP loci, 15% were outliers across multiple population comparisons, and low linkage disequilibrium indicated that these outliers derived from multiple regions of the genome. Outliers were further classified as host-specific if repeatedly observed in different-host population comparisons but never in same-host comparisons. Outliers exhibiting the opposite pattern were analogously classified as host-independent. Host-specific outliers represented 5% of all loci and were more frequent than host-independent outliers, thus revealing a large role for host-adaptation in population genomic differentiation. Evidence that host-related selection can promote divergence despite gene flow was provided by population trees. These were structured by host-association when datasets included host-specific outliers, but not when based on neutral loci, which united sympatric populations. Lastly, three host-specific outliers were highly differentiated in all nine different-host comparisons. Because host-adaptation promotes reproductive isolation in these beetles, these loci provide promising candidate gene regions for future molecular studies of ecological speciation.
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