Hybridization fuelled diversification in Spialia butterflies

The importance of hybridization and introgression is well documented in the evolution of plants but, in insects, their role is not fully understood. Given the fact that insects are the most diverse group of organisms, assessing the impact of reticulation events on their evolution may be key to comprehend the emergence of such remarkable diversity. Here, we used an insect model, the Spialia butterflies, to gather genomic evidence of hybridization as a promoter of novel diversity. By using double-digest RADseq (ddRADseq), we explored the phylogenetic relationships between Spialia orbifer, S. rosae and S. sertorius, and documented two independent events of interspecific gene flow. Our data support that the Iberian endemism S. rosae probably received genetic material from S. orbifer in both mitochondrial and nuclear DNA, which could have contributed to a shift in the ecological preferences of S. rosae. We also show that admixture between S. sertorius and S. orbifer probably occurred in Italy. As a result, the admixed Sicilian populations of S. orbifer are differentiated from the rest of populations both genetically and morphologically, and display signatures of reproductive character displacement in the male genitalia. Additionally, our analyses indicated that genetic material from S. orbifer is present in S. sertorius along the Italian Peninsula. Our findings add to the view that hybridization is a pervasive phenomenon in nature and in butterflies in particular, with important consequences for evolution due to the emergence of novel phenotypes.