Comparative analysis of multiple hybrid zones of Rhododendron × duclouxii uncovered different potential evolutionary outcomes

The study of natural hybridization facilitates our understanding of potential adaptive mechanisms in evolution and the process involved in speciation. In this study, we used multiple data types, including morphological traits, ddRAD-seq and ecological niche data, to investigate the differences among Rhododendron × duclouxii hybrid zones and the mechanisms underlying natural hybridization and possible future evolutionary pathways. Our results show that the origins of each hybrid zone are independent, with variations in hybrid formation, structural characteristics, and patterns of genetic components and morphological trait differentiation. There were no significant differences in morphological traits or genetic variation between the F1 and F2 generations; however, the range of variation of the F2 generation was broader than that of the F1 generation. The distribution and ecological characteristics of R. × duclouxii did not significantly differ from those of the two parental species, indicating weak ecological niche preferences between the hybrid and parental taxa. These results imply that the hybrid zones of R. × duclouxii are characterized by considerable variability, with the magnitude of hybridization in each case likely influenced by unique combinations of biological and ecological factors specific to each hybrid zone. We predict that R. × duclouxii hybrid zones will persist and give rise to complex hybrid swarms, each potentially leading to different evolutionary outcomes.