Abstract: Differentiation among populations, sometimes despite ongoing gene exchange, is a key step in speciation. Therefore, comparison of intra- and interspecific differentiation patterns is of great significance to understanding speciation. The genus Quercus is an interesting system to test speciation models in the presence of gene flow, due to its weak interspecific reproductive barriers. The aim of the present study was to characterize the degree and pattern of morphological and genetic differentiation among different morphotypes in the white oak Quercus laeta, some corresponding to the previously described species Quercus centralis, Q. laeta, Quercus prinopsis, and Quercus transmontana, as well as geographically structured variation within Q. transmontana not described previously. Our goal was to evaluate if some of these can be considered distinct specific entities or are rather part of a continuum of variation. Nine microsatellite loci and two intergenic regions of chloroplast DNA were analyzed. Morphological differences were evaluated using geometric morphometrics. Chloroplast DNA showed low differentiation, suggesting introgression or sharing of ancestral haplotypes among the Q. laeta morphotypes. Nuclear microsatellites indicated differentiation into two distinct main genetic groups, which were congruent with morphological differentiation. In conclusion, nuclear markers and morphological variations suggest the existence of at least two different entities within Q. laeta.

Key words: gene flow, genetic differentiation, leaf morphometrics, microsatellite loci, morphotype, population assignment, species delimitation