Multimarker Analysis Reveals Ecological Islands in Hybrid Complexes: The Case of Quercus castanea × Q. crassipes Complex (Fagaceae) in Central Mexico

Hybridization is frequent in oaks and may drive various evolutionary and ecological effects on involved plant populations and their associated species. Quercus castanea is a species of Mexican red oak that has served as a valuable model for examining the effects of hybridization events. We used a multimarker approach to characterize the morphological expression patterns and chemical production in parental and hybrid genotypes of the Q. castanea × Q. crassipes complex in a hybrid zone in central Mexico. Leaf macro- and micro-morphological (stomata) characters were measured in 27 trees previously recognized as Q. castanea, Q. crassipes, and hybrids (nine trees/taxon). The expression of foliar shape and the production of secondary metabolites and nutritional chemicals between hybrids and parental species were also evaluated. We found that hybrids exhibit a mosaic of macro- and micro-morphological characters, including the expression of intermediate, parental, and transgressive attributes. Parental species were well differentiated based on foliar shapes, with hybrids overlapping in both species, having a greater affinity with Q. crassipes. Chemical analysis also supports three chemical groups, with hybrids producing new metabolites. This multimarker approach evidences the formation of ecological islands in this hybrid oak complex in which Q. castanea is involved, a fact that has consequences at higher levels of organization in ecology.