Demography‐driven and adaptive introgression in a hybrid zone of theArmeriasyngameon

Abstract

AbstractSyngameons represent networks of otherwise distinct species connected by limited gene exchange. Although most studies have focused on how species maintain their cohesiveness despite gene flow, there are additional relevant questions regarding the evolutionary dynamics of syngameons and their drivers, as well as the success of their members and the network as a whole. Using a ddRADseq approach, we analysed the genetic structure, genomic clines and demographic history of a coastal hybrid zone involving two species of theArmeria(Plumbaginaceae) syngameon in southern Spain. We inferred that a peripheral population of the sand dune‐adaptedA. pungensdiverged from the rest of the conspecific populations and subsequently hybridized with a locally more abundant pinewood congener,A. macrophylla. Both species display extensive plastid DNA haplotype sharing. Genomic cline analysis identified bidirectional introgression, but more outlier loci with excessA. pungensthanA. macrophyllaancestry, suggesting the possibility of selection forA. pungensalleles. This is consistent with the finding that theA. pungensphenotype is selected for in open habitats, and with the strong correlation found between ancestry and phenotype. Taken together, our analyses suggest an intriguing scenario in which bidirectional introgression may, on the one hand, help to avoid reduced levels of genetic diversity due to the small size and isolated location of theA. pungensrange‐edge population, thereby minimizing demographic risks of stochastic extinction. On the other hand, the data also suggest that introgression intoA. macrophyllamay allow individuals to grow in open, highly irradiated, deep sandy, salt‐exposed habitats.