Exchange of genetic material among species played a major role in the wide diversity of Heliconius butterflies, according to a new study, results of which inform a centuries-long debate about the value of hybridization to species evolution. The work "documents the importance of hybridization on genomic evolution in unprecedented detail," writes Loren Rieseberg in a related Perspective. The study also offers a new genomic approach to disentangle the genetic contributions of hybridization from other genetic change processes, showing how the former can provide the genetic material necessary for rapid, adaptive divergence and radiation in species. The importance of hybridization in evolution has been a highly debated topic. Heliconius, a diverse genus of butterfly comprised of at least 40 species, is known for its colorful and highly unique wing patterns. Because of this diversity, the species have been useful in studying gene exchange among species. However, given the difficulty in distinguishing DNA as derived from other lineages throughout time from genetic change processes like incomplete lineage sorting, the role of hybridization Heliconius diversity remains questioned. Nathaniel Edelman and colleagues generated 20 genome assemblies for species of Heliconius that hadn't been well-studied, and for related genera. Using a new method they designed to specifically detect genetic variation introduced through hybridization, Edelman et al. uncovered a significant influence of hybridization on the evolutionary history of Heliconius across the genomes they sampled. Hybridization's impact, they say, varies with factors like gene density and genome architecture. The authors also reported on a new chromosomal structure likely shaped by hybridization that includes the cortex locus, which has been shown to underlie the evolution of wing coloration patterns and mimicry in another Heliconius species. This suggests hybridization had a beneficial consequence in the evolution and adaption of Heliconius. "This study adds to a growing literature indicating that the footprints of hybridization are a common feature of plant and animal genomes and that hybridization can provide the fuel for adaptive diversification," writes Rieseberg.
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Journal
Science