Patterns of speciation in a parapatric pair of Saturnia moths as revealed by Target Capture

The focus of this study is to understand the evolutionary relationships and taxonomy of widely distributed parapatric species pair of wild silk moths, Saturnia pavonia and Saturnia pavoniella (Lepidoptera: Saturniidae) in Europe. To address species delimitation challenges associated with many parapatric taxa, target enrichment and mtDNA sequencing was employed alongside phylogenetic, species delimitation, admixture and introgression analyses. The dataset included individuals from both species, two hybrids generated in the lab, as well as individuals from outside the contact zone. Nuclear markers strongly supported both S. pavonia and S. pavoniella as two distinct species, with the hybrids grouping together as intermediate and separate from both species. However, the maximum likelihood (ML) tree generated from mtDNA sequencing data presented a different picture, showing both taxa to be phylogenetically intermixed. This inconsistency may be attributed to mitonuclear discordance, which can arise from biological factors (e.g., introgressive hybridization or incomplete lineage sorting) or alternatively operational factors (e.g., incorrect species delimitation). We further provide the evidence of past introgression to have taken place, but no evidence of current admixture between the two species. Finally, we discuss our results from evolutionary point of view taking into consideration the past climatic oscillations that has likely shaped the present dynamics between the species. Overall, this study demonstrated the effectiveness of the target enrichment approach in resolving the phylogenetic relationships between closely related parapatric species and providing insights into their taxonomic delimitation.