A genome-wide AFLP replacement in a hybrid population derived from two closely related Viola species from contrasting habitats

Hybrid zones formed from genetically and ecologically differentiated species provide an opportunity to examine how genetics and ecology interact to determine species boundaries. In this study, we examined a hybrid zone generated by invasion of shade-loving Viola eizanensis into habitat occupied by its close relative, V. chaerophylloides var. sieboldiana, which prefers more open areas. We used 339 AFLP loci to estimate genomic composition and generation of hybrids, and confirmed maternal inheritance through sequencing of the cpDNA atpI–atpH intergenic spacer region. Phenotypic variation was assessed using leaf thickness (leaf mass/area) and leaf dissection (leaf perimeter/area), which were diversified between species. Genetic analyses showed that the AFLP of hybrid individuals in having maternal origin from V. chaerophylloides var. sieboldiana were replaced by V. eizanensis in response to habitat. Significant correlations were observed between hybrid indices and the two leaf traits. These results suggest that genes of V. eizanensis that are adaptive to shaded habitats are fixed in the hybrids, and that the degree of leaf thickness and dissection is important in adaptation of the hybrids to their light environments.