Preliminary characterization of the Quercus pubescens complex in southern Italy using molecular markers

Abstract

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.

A multivariate morphometric analysis of diagnostic traits in southern Italy and Sicily pubescent oaks

“…However, as underlined in Denk et al (2017), the major challenge for future studies is to establish the molecular and morphological circumscription at species rank and their biogeographic and ecological characterization. In the last two decades important results have been achieved in identifying the occurrence (or the absence) of species boundaries between taxonomically critical groups of sympatric Southern-European white oaks using molecular markers (Bruschi et al 2000;Jedináková-Schmidtová et al 2004;Franjic et al 2006;Fortini et al 2009;Curtu et al 2011;Enescu et al 2013;Crăciunescu et al 2015;Di Pietro et al 2020). In our opinion, the necessary further step should be to link discontinuities highlighted at the genomic level to a well-defined and unambiguous set of diagnostic morphological, ecological and coenological characters to circumscribe oak species.…”

Does the genetic diversity among pubescent white oaks in southern Italy, Sicily and Sardinia islands support the current taxonomic classification?

“…As already mentioned in the introduction, some authors consider these taxa as valid species while others consider them as morphotypes included in the natural morphological variability of Q. pubescens Willd. The morphological characters used to distinguish these taxa are for the most part quantitative characters (Di Pietro et al 2020) with overlapping values between species in the identification keys. For this reason, and to ensure that both the choice of collection sites and the interpretation of the results of the genetic analysis were subject to the lowest possible degree of subjectivity, we have preferred to maintain a neutral position regarding the name of the species, avoiding to provide our a priori identification.…”

“…This set of EST-SSR markers (PIE) was chosen according to other recent studies on European white oaks (Lepais et al 2009;Guichoux et al 2011a, b;Neophytou et al 2010;Curtu et al 2015;Antonecchia et al 2015;Di Pietro et al 2020). The primer pairs were combined into three different Table 2).…”

“…In fact, the debate on the taxonomic value of all these pubescent oak species is very heated throughout Europe. Nonetheless there are very few studies that addressed the problem of oak taxonomy using a multidisciplinary approach where molecular analyses are carried out in support of previous morphological analyses (Franjic et al 2006;Di Pietro et al 2016, 2020Musarella et al 2018). While it is true that cpDNA markers can be useful to establish the conformity of a given material to the populations of its origin and to trace possible routes of migration at a broad geographic scale, cpDNA provides limited taxonomic information on the systematic status of interfertile, sympatric species (see Curtu et al 2007a, b;Neophytou and Michiels 2013;Blanc-Jolivet and Liesebach 2015).…”

“…In contrast, co-dominant markers, such as microsatellites, have successfully been tested to study genetic structures and distinguish oak species at regional or local scale (Degen et al 1999;Gomory 2000;Gugerli et al 2007;Guicoux et al 2011b;Hoeltken et al 2012). Only recently, population genetic studies based on co-dominant nuclear markers have been carried out in white oak populations from restricted areas of southern Italy (Antonecchia et al 2015;Fortini et al 2015;Di Pietro et al 2016, 2020. These studies were based on sampling protocols, which provided a high number of reference samples per population and a high number of populations per unit area.…”