Interfertile oaks in an island environment. II. Limited hybridization between Quercus alnifolia Poech and Q. coccifera L. in a mixed stand

Abstract

Hybridization and introgression betweenQuercus alnifolia Poech and Q. coccifera L. is studied by analyzing morphological traits, nuclear and chloroplast DNA markers. The study site is a mixed stand on Troodos Mountains (Cyprus), and the analyzed material includes both adult trees and progenies of specific mother trees. Multivariate analysis of morphological traits shows that the two species can be well distinguished using simple leaf morphometric parameters. A lower genetic diversity in Q. alnifolia than in Q. coccifera and a high interspecific differentiation between the two species are supported by an analysis of nuclear and chloroplast microsatellites. The intermediacy of the four designated hybrids is verified by both leaf morphometric and genetic data. Analysis of progeny arrays provides evidence that interspecific crossings are rare. This finding is further supported by limited introgression of chloroplast genomes. Reproductive barriers (e.g. asynchronous phenology, postzygotic incompatibilities) might account for this result. A directionality of interspecific gene flow is indicated by a genetic assignment analysis of effective pollen clouds with Q. alnifolia acting as pollen donor. Differences in flowering phenology and species distribution in the stand may have influenced the direction of gene flow and the genetic differentiation among effective pollen clouds of different mother trees within species.

Differences in growth, survival and phenology in Quercus rubra and Q. ellipsoidalis seedlings

“…Significantly later bud burst in Q. ellipsoidalis seedlings when compared with seedlings from the Q. rubra populations including the neighboring population FC-B suggest differences in the timing of bud burst as a mechanism of pre-zygotic isolation between species. Thus, analyses in European white oaks showed a strong association between the timing of vegetative bud burst and flowering time (Chesnoiu et al 2009;Franjic et al 2011;Neophytou et al 2011). Likewise, autumn senescence occurred significantly later in Q. ellipsoidalis than in Q. rubra seedling populations reflecting genetic differences in phenology traits between seedlings of both species.…”

An updated infrageneric classification of the oaks: review of previous taxonomic schemes and synthesis of evolutionary patterns

“…This is mainly because the plastid genealogy is largely decoupled from taxonomy and substantially affected by geography (e.g. Neophytou et al 2010;Neophytou et al 2011;Simeone et al 2016;Pham et al 2017). Using genus-to family-level plastid data sets, even when combined with nuclear data, oaks are consistently recognised as a diphyletic group.…”

Fine-scale spatial genetic structure in a multi-oak-species (Quercus spp.) forest

“…Ten highly polymorphic microsatellite markers were used: QrZAG112, QrZAG96, QrZAG11, Qr-ZAG20, QrZAG7, QrZAG87 (Kampfer et al 1998), QpZAG110, QpZAG9 (Steinkellner et al 1997) PIE215 and PIE223 (Durand et al 2010). These microsatellite markers are among those selected to genotype European oak species in recent studies (Lepais et al 2009, Guichoux et al 2011, Neophytou et al 2011. Several other markers were tested (e.g., QrZAG39 and QrZAG5b), but they were removed from the population screening due to the presence of null alleles or because the genotypes could not be reliably scored.…”