Genomics of an adaptive radiation in Heliconius butterflies

Understanding how adaptive phenotypes arise is vital for understanding the origins of biodiversity and for predicting how organisms will respond to novel selective pressures. Despite this importance, there are still only a handful of examples where the specific genetic changes underlying adaptive phenotypic variation in nature have been identified. The adaptive radiation of wing color patterns in Heliconius butterflies is one of these few examples that the natural diversity and genomic resources are available. For example, Heliconius erato has undergone a remarkable adaptive radiation, diversifying into 23 distinctively different color-pattern races and we have mapped and sequenced the three major loci responsible for this diversity. Full genome re-sequencing of individuals from natural hybrid zones has allowed us to identify narrow genomic regions controlling each of these three color pattern loci. One of the loci (D), we have narrowed to a 65kb region containing the regulatory change responsible for the red pattern variation. We have narrowed the functional site to ~74 polymorphic sites that have fixed allelic differences between differently patterned individuals. Using this region, we reconstructed the evolutionary history of red wing patterns, which revealed that distant races and species sharing similar red patterns, likely share a common origin of their red patterns. The wing patterns of Heliconius offer a direct connection between adaptive variations in phenotype and genotype in a well-studied system, which can provide an unprecedented integrative understanding of the general nature of adaptive change.