Abstract
Dehydryn genes are involved in plant response to environmental stress and may be useful to examine functional diversity in relation to adaptive variation. Recently, a dehydrin gene (DHN3) was isolated in Quercus petraea and showed little differentiation between populations of the same species in an altitudinal transect. In the present study, inter- and intraspecific differentiation patterns in closely related and interfertile oaks were investigated for the first time at the DHN3 locus. A four-oak-species stand (Quercus frainetto Ten., Q. petraea (Matt.) Liebl., Q. pubescens Willd., Q. robur L.) and two populations for each of five white oak species (Q. frainetto Ten., Q. petraea (Matt.) Liebl., Q. pubescens Willd., Q. robur L. and Q. pedunculiflora K. Koch) were analyzed. Three alleles shared by all five oak species were observed. However, only two alleles were present in each population, but with different frequencies according to the species. At population level, all interspecific pairs of populations showed significant differentiation, except for pure Q. robur and Q. pedunculiflora populations. In contrast, no significant differentiation (p > 0.05) was found among conspecific populations. The DHN3 locus proved to be very useful to differentiate Q. frainetto and Q. pubescens from Q. pedunculiflora (FST = 0.914 and 0.660, respectively) and Q. robur (FST = 0.858 and 0.633, respectively). As expected, the lowest level of differentiation was detected between the most closely related species, Q. robur and Q. pedunculiflora (FST = 0.020). Our results suggest that DHN3 can be an important genetic marker for differentiating among European white oak species.
Highlights
The genus Quercus L. comprises roughly 500 species (Aldrich and Cavender-Bares, 2011) subdivided into several distinct monophyletic groups (Manos et al, 1999; Manos and Stanford 2001)
Our results suggest that DHN3 can be an important genetic marker for differentiating among European white oak species
Similar results were reported in a gene coding for a non-specific NAD-dependent dehydrogenase (Gömöry, 2000), where the interspecific component of variation accounted for 54.3% of the total gene diversity and 43.5% of total variation was distributed within populations
Summary
The genus Quercus L. comprises roughly 500 species (Aldrich and Cavender-Bares, 2011) subdivided into several distinct monophyletic groups (Manos et al, 1999; Manos and Stanford 2001). While the permeable ones share introgressed genes that decrease interspecific differentiation, the impermeable regions are responsible for the maintenance of species integrity because they accumulate divergence in response to selection This theory is supported by several studies in interfertile plant and animal species (Barton and Gale, 1993; Via and West, 2008), as well as in the Quercus spp. complex (Scotti-Saintagne et al, 2004). From this point of view, one can better understand the antagonistic effects of interspecific gene flow and divergent selection which causes the low genetic differentiation between hybridizing oak species at most genomic regions and the high interspecific differentiation at several ‘islands’ (outlier regions), respectively. This pattern is consistent with the expected spatial clustering of outlier markers due to ecological speciation (Via, 2009)
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