Discussion
Our study provides valuable insights into the population genetics of theC . variipennis species complex and highlights the presence
of potential cryptic species. For most of the species examined, minimal
genetic divergence was observed across populations, suggesting the
maintenance of gene flow even over large geographic distances. The only
exception was C. occidentalis , which showed a high level of
geographic isolation, as well as two distinct genetic clusters. We
confirmed that mitochondrial data is not reliable to properly
differentiate three out of five species, due to the lack of segregation
between the mitochondrial haplotypes of C. albertensis , C.
sonorensis , and C. variipennis . This stands in stark contrast to
their clear differentiation and high level of divergence inferred from
the SNP data. Though a substantial amount of divergence exists between
all five species, hybridization and introgression are present at low
levels in sympatry suggesting that post-zygotic isolation barriers have
not evolved in this group. Thus, pre-zygotic isolation through either
ecological or behavioral segregation is likely responsible for
divergence within this complex. With a considerable amount of overlap
between some species (Fig. 1), each sympatric population is potentially
experiencing a set of unique selective pressures to maintain species
boundaries.