Evolutionary implications of spatial variation in sexual traits in the Satyrium fuliginosa/semiluna complex (Lycaenidae)

Secondary contact between partially divergent lineages can either reinforce or reduce pre-zygotic reproductive barriers. Satyrium semiluna and S. fuliginosa (Lycaenidae: Theclinae) are cryptic sexually-monomorphic hairstreaks found in isolated subalpine and steppe habitats of the western North America. Delimitation of the taxa is largely based on the relative presence and absence of the male androconial patch (the “stigma”). Androconial scales are believed to produce pheromones critical to courtship, and therefore should be phylogenetically conserved. Phylogenetic evidence suggests that the absence of the stigma in S. fuliginosa represents a derived loss. Using sequence data and AFLPs, I have documented a narrow hybrid zone in the California Sierra Nevada that also corresponds with populations with polymorphic wing phenotypes. This introgression appears unidirectional, with S. semiluna alleles being introduced into S. fuliginosa. All males from populations with signs of hybridization lack the stigma (“S. fuliginosa”), but most of these are roughly 2:1 genomic admixtures of S. fuliginosa and S. semiluna, and the majority (to near fixation in one population) possess the mitochondrial signatures of stigma-bearing S. semiluna. Individuals from all pairwise combinations of populations from this contact zone will mate in captivity, but wild males from most populations (regardless of taxon) generally prefer to court females from S. semiluna populations under wild conditions. The combination of genomic data and field behaviors suggests that S. fuliginosa and S. semiluna are not reproductively isolated and S. fuliginosa may retain preferences for S. semiluna characteristics.