Genetic analysis of wing pattern and pheromone composition in two sister species of Heliconius butterflies.

The problem of sympatric speciation and speciation with gene flow has been of great interest to evolutionary biologists for years. While both concepts were highly debated in the past, it is now known that both events are possible. Ecological factors can come into play to encourage species divergence in sympatry, with different selective pressures giving rise to different adaptive phenotypes within the same territory, thereby forming separate races within a population that can eventually evolve into fully separate species. When this happens, gene flow may be partially retained between the incipient species as they diverge. But gene flow and divergent selection do not affect all parts of the genome equally: novel adaptations that promote speciation tend to accumulate in specific regions known as islands of divergence, that can act as reproductive barriers between the diverging taxa. Understanding the genetics of traits that are leading speciation is thus of great importance in the study of evolution, and Heliconius butterflies offer a great model system for researching this phenomenon. In this study, hybrid individuals are used to characterize the genetic structure of two traits that are likely to have this role, the colour pattern and the pheromone blend, in two sister species of Heliconius butterflies, H. pardalinus butleri and H. elevatus. Several putative colour pattern loci were found, potentially arranged into 2-3 linkage groups, consistent with the arrangement observed in other Heliconius species. The biosynthetic machinery underlying pheromone production in Heliconius was also partially characterized for the first time by investigating correlations between compounds within the F2 hybrids, which also offered insight into the genetic organization of pheromone genes.