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

TITLE: 1 Detecting interspecific and geographic differentiation patterns in two interfertile oak 2 species (Quercus petraea (Matt.) Liebl. and Q. robur L.) using small sets of 3 microsatellite markers 4 5 AUTHORS: 40 2 1 2 ABSTRACT 3 4 Genetic analysis was carried out in order to provide insights into differentiation 5 among populations of two interfertile oak species, Quercus petraea and Quercus 6 robur. Gene flow between the two species, local adaptations and speciation 7 processes in general, may leave differential molecular signatures across the genome. 8 Three interspecific pairs of natural populations from three ecologically different 9 regions, one in central Europe (SW Germany) and two in the Balkan Peninsula 10 (Greece and Bulgaria) were sampled. Grouping of highly informative SSR loci was 11 made according to the component of variation they express – interspecific or 12 provenance specific. 'Species' and 'provenance discriminant' loci were characterized 13 based on F ST s. Locus specific F ST s were tested for deviation from the neutral 14 expectation both within and between species. Data were then treated separately in 15 a Bayesian analysis of genetic structure. By using three 'species discriminant' loci, 16 high membership probability to inferred species groups was achieved. On the other 17 hand, analysis of genetic structure based on five 'provenance discriminant' loci was 18 correlated with geographic region and revealed shared genetic variation between 19 neighbouring Q. petraea and Q. robur. Small sets of highly variable nuclear SSRs were 20 sufficient to discriminate, either between species or between provenances. Thus, an 21 effective tool is provided for molecular identification of both species and 22 provenances. Furthermore, data suggest that a combination of gene flow and natural 23 selection forms these diversity patterns. 'Species discriminant' loci might represent 24 genome regions affected by directional selection, which maintains species identity. 25 'Provenance specific' loci might represent genome regions with high interspecific 26 gene flow and common adaptive patterns to local environmental factors. 27 28 29 KEY WORDS: Microsatellites, genetic differentiation, genetic structure, genetic 30 introgression, 'species discriminant loci', 'provenance discriminant loci'. 31 32 3 1. INTRODUCTION 1 2 Since Darwinian times, oaks have served as a model genus for studying evolutionary 3 processes and speciation. High adaptability and high levels of interspecific gene flow 4 were among the features which significantly contributed to the genesis of several 5 Species identification and characterization have often been a 7 …