Detecting interspecific and geographic differentiation patterns in two interfertile oak species (Quercus petraea (Matt.) Liebl. and Q. robur L.) using small sets of microsatellite markers

Genetic analysis was carried out in order to provide insights into differentiation among populations of two interfertile oak species, Quercus petraea and Quercus robur. Gene flow between the two species, local adaptation and speciation processes in general, may leave differential molecular signatures across the genome. Three interspecific pairs of natural populations from three ecologically different regions, one in central Europe (SW Germany) and two in the Balkan Peninsula (Greece and Bulgaria) were sampled. Grouping of highly informative SSR loci was made according to the component of variation they express—interspecific or provenance specific. ‘Species’ and ‘provenance discriminant’ loci were characterized based on F_STs. Locus specific F_STs were tested for deviation from the neutral expectation both within and between species. Data were then treated separately in a Bayesian analysis of genetic structure. By using three ‘species discriminant’ loci, high membership probability to inferred species groups was achieved. On the other hand, analysis of genetic structure based on five ‘provenance discriminant’ loci was correlated with geographic region and revealed shared genetic variation between neighbouring Q. petraea and Q. robur. Small sets of highly variable nuclear SSRs were sufficient to discriminate, either between species or between provenances. Thus, an effective tool is provided for molecular identification of both species and provenances. Furthermore, data suggest that a combination of gene flow and natural selection forms these diversity patterns. ‘Species discriminant’ loci might represent genome regions affected by directional selection, which maintains species identity. ‘Provenance specific’ loci might represent genome regions with high interspecific gene flow and common adaptive patterns to local environmental factors.     

Differences in Species Composition and Stand Characteristics of Mixed Upland Hardwood Forests of North Alabama as Reflected by the Presence of Eastern Redcedar (Juniperus virginiana L.)

The mixed hardwood forests of North Alabama and adjacent states contain stands of varied specks composition and stand structure, with much variation associated with the presence of Eastern redcedar (Juniperus viginiana L.) within the stands. This study quantified the composition of 44 stands within these forests with discriminate analysis, cluster analysis and tree area ratio modeling. Little variation in the presence of specific species was found on plots with Eastern redcedar when compared to plots without this species, but the number of individuals and their portion of the total stand structure did vary between the two types of stands. Twenty-seven species were grouped into six clusters, with associated species differing between plots with and without eastern redcedar. Eastern redcedar sites did appear to reflect lower productivity, with the trees smaller in diameter and shorter in height. Additional stand structure information is also discussed.