Conclusion
Our study shows that using a population genomic approach to studying sibling species can identify both species-level divergence as well as fine-scale genetic structuring. Tracing the level of gene flow within and between these species enables the detection of geographic isolation, hybridization, and cryptic species to offer a more accurate depiction of the current species dynamics. Radiation within the C. variipenniscomplex occurred despite the long-range dispersal capabilities of biting midges as well as hybridization between sympatric species. Because of this, we believe that behavioral and ecological isolation may have shaped evolution within this group or is at least maintaining the existing species boundaries. Significant geographic isolation was only found between populations of C. occidentalis , but more work is needed to determine if the lack of gene flow between California and the other populations represents an incipient speciation event. Delimiting the species in the C . variipennis complex will not only aid in vector surveillance efforts, but continued study of the speciation of closely related vector and non-vector species could produce valuable evolutionary insights into vector competency.