Coincidence of Small-scale Spatial Discontinuities in Leaf Morphology and Nuclear Microsatellite Variation of Quercus petraea and Q. robur in a Mixed Forest

Abstract

The spatial-genetic analyses and the available literature led to the assumption that reproductive barriers, assortative mating, limited seed dispersal and microsite-induced selection in favour of the locally adapted taxon at the juvenile stage may reinforce taxon-specific spatial aggregation that fosters species separation. Thus, the results tend to support the hypothesis that Q. petraea and Q. robur are distinct taxa which share a recent common ancestry. Occasional hybrids are rarely found in adults owing to selection during establishment of juveniles.

Genetic evidence of reproductive isolation in a remote enclave of Quercus pubescens in the presence of cross-fertile species

“…In general, sharp genetic delineation between sympatric species is not very new for the European white oak complex. Several authors have recently found strong genetic separation of species in mixed stands across the main range of coexistence of different oak species (Gugerli et al 2007;Curtu et al 2007;Lepais et al 2009). However, our results provide new evidence for strong reproductive barriers and/or selection mechanisms among European oak species that shape their ecology and evolution at the Northern range margin.…”

“…Given the strong introgression pressure suggested above, the question remains how then the apparent separation of the gene pool of Q. pubescens in Bielinek can be explained. Three mutually non-exclusive possibilities could occur: (1) reproductive barriers, (2) microsite selection and (3) assortative mating (Bruschi et al 2000;Curtu et al 2007;Gugerli et al 2007;Varela et al 2008;Lepais et al 2009). Controlled pollination experiments revealed that oaks in the studied species complex are potentially interfertile (Steinhoff 1993;Orlik and Kjaer 2007).…”

“…The three oaks differ substantially in their ecological optima, causing usually spatial species separation within mixed oak populations (e.g. Bacilieri et al 1996;Curtu et al 2007;Gugerli et al 2007). Because the study site is characterised by shallow soils, a steep slope and southern exposition, Q. pubescens may outcompete both common oak species due to relatively high tolerance to drought.…”

“…To strengthen the power of multilocus clustering analysis (see below), we included the loci that appeared to be highly discriminative in the earlier studies on European white oaks (e.g. Curtu et al 2007;Gugerli et al 2007;Lepais et al 2009). PCR products were sized using an ABI 3130XL sequencer (Applied Biosystems, Foster City, CA, USA) and the attached software (Genemapper 4.0).…”

“…Related oak species can hybridise relatively easily, and hybrids are usually fertile (Whittemore and Schaal 1991;Rushton 1993;Tovar-Sánchez and Oyama 2004;Curtu et al 2007;Peñaloza-Ramírez et al 2010). Furthermore, related oak species can differ in ecological optima (Whittemore and Schaal 1991;Timbal and Aussenac 1996;Petit et al 2004;Sánchez de Dios et al 2006;Gugerli et al 2007), so that they often occupy different niches and can reveal variable adaptation to local environments, making room for exogenous selection (Barton and Hewitt 1985).…”