Morphological and genetic differentiation in isolated populations of Mexican beech Fagus grandifolia subsp. mexicana

Abstract

Mexican beech [Fagus grandifolia subsp. mexicana (Martinez) A.E.Murray] is a subspecies endemic to the Sierra Madre Oriental Mountains and considered endangered due to the low density of its populations and high degree of habitat fragmentation and environmental specificity. Because its morphological and genetic variation is associated with its ability to adapt to changes in environmental conditions, the objective of this study was to determine whether phenotypic and genotypic variation exist, and it relationships with population reduction events. In four beech populations in the states of Hidalgo and Veracruz, we analyzed 11 morphological variables for leaves and 6 microsatellite markers. The morphological variables that to discriminate between populations were related to the size of the leaf, but a robust differentiation pattern was not found, given that independent groups of leaves were identified. The populations located closest to each other, had greater genetic variation and less genetic distance; populations in the extreme north and south had the lowest genetic variation. Genetic differentiation among populations was associated with reduction in population size. In the 3 localities in Hidalgo, recent bottlenecks were identified, and in Veracruz, an old bottleneck was found. Variation in leaf morphology and genetic structure of Mexican beech populations could be the result of a combination of various geographical, climate and ecological factors.