Antonecchia G., Fortini P., Lepais O., Gerber S., Legér P., Scippa G.S., Viscosi V., 2015. Genetic structure of a natural oak community in central Italy: Evidence of gene flow between three sympatric white oak species (Quercus, Fagaceae). Ann. For. Res. 58(2): 205-216.Abstract. Incomplete reproductive barriers between species, especially in sympatric areas where several species coexist, may result in hybridization and an increase in genetic diversity. Here we assessed the amount of genetic diversity in a community of three interfertile and sympatric European oaks (Quercus frainetto Ten., Q. petraea Liebl. Matt. and Q. pubescens Willd.) situated in central Italy. We used 11 microsatellite markers derived from Expressed Sequence Tag (EST-SSRs) and we implemented a Bayesian clustering analysis to assign individuals to species or hybrids. All genotyped loci were polymorphic for all the species and three genetic clusters corresponding to each species were detected. Significant differences and a higher level of gene flow were observed between the three oak species. Occurrence of hybrids varied markedly within the studied area: hybrids between Q. petraea and Q, pubescens were the most frequent, while hybrids between Q. petraea and Q. frainetto were particularly rare. Q. pubescens and Q. petraea showed the highest number of alleles compared to Q. frainetto, which was characterized by a low number of private, but highly frequent, alleles. However, Q. frainetto showed a lower genetic diversity and a stronger reproductive isolation from the other two oak species.
Quercus pubescens s.l. is a group of taxonomically intricate and highly debated deciduous white oaks widely distributed in southern Europe. The Apulia Region occupies the south-easternmost part of the Italian peninsula; the land-use pattern is based on extensive agricultural systems and only 10% is covered by forests that are mainly composed of oak woods. It is the region in Italy showing the highest number of oak species, among which four putative species of the Quercus pubescens group, have been reported in floras and checklists with uncertain taxonomic value because of the overlapping of diagnostic characters. In this paper, we carried out a molecular analysis on natural populations of Q. pubescens s.l. distributed throughout the Apulian region. Individuals from 24 pubescent oak populations were sampled and each tree was genotyped at 11 polymorphic microsatellite markers. Overall, the average expected heterozygosity (He) was 0.629, and the allelic richness (Ar) ranged between 2.130 and 7.187. No differentiation was observed among the populations investigated, and the genetic differentiation coefficient (FST) was 0.036. Gene flow among populations was found to be relatively high (Nm = 6.664). From a taxonomic point of view, the possibility of the coexistence of more than one species among the Apulian pubescent oaks reported in the taxonomic and syntaxonomic literature is not supported by the results of this molecular analysis.
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