Population differentiation of sessile oak at the altitudinal front of migration in the French Pyrenees

Abstract

To assess the effects of altitude on the level and structure of genetic diversity, a genetic survey was conducted in 12 populations of sessile oak (Quercus petraea) located between 130 and 1660 m in two parallel valleys on the northern side of the Pyrenees Mountains. Genetic diversity was monitored at 16 nuclear microsatellite loci and 5 chloroplast DNA (cpDNA) markers. The cpDNA survey suggested that extant populations in both valleys shared the same source populations from the plain. There was no visible trend of nuclear genetic diversity along altitude, even if indirect estimates of effective population sizes revealed a consistent reduction at higher altitudes. Population differentiation, although low, was mostly present among populations of the same valleys and reached similar levels than differentiation across the range of distribution of sessile oak. Contribution to the overall differentiation in the valleys was mostly due to the genetic divergence of the highest populations and the altitudinal variation of allelic frequencies at a few loci. Bayesian inference of migration between groups of populations showed that gene flow is preferentially unidirectional from lower altitudes in one valley to other groups of populations. Finally, we found evidence of clonal reproduction in high altitude populations. The introgression of Quercus robur and Quercus pubescens was also more frequent at the altitudinal margin suggesting that this mechanism may have contributed to the present migration and adaptation of Q. petraea and may also facilitate its future upslope shift in the context of climate change.

Long prereproductive selection and divergence by depth in a Caribbean candelabrum coral

“…The long period between when a larva settles and when it becomes a colony that contributes genetically to the next generation thus decreases gene flow between depth-adapted lineages and enhances the opportunity for habitat-specific selection and divergent adaptation. Such immigrant inviability may be common in slowly maturing sessile species with broad dispersal [like some scrubs and trees (53,54)]. In contrast, when adults are the primary dispersers, immigrant inviability would have to be exceptionally strong to have such an effect, as migrants can reproduce as soon as they settle, allowing locally adapted genotypes to mix with maladapted foreign ones.…”

Imprints of Natural Selection Along Environmental Gradients in Phenology-Related Genes ofQuercus petraea

“…To account for false positives resulting from these historical and demographic mechanisms we checked for isolation by distance by calculating pairwise comparisons of population differentiation with the geographic distance (Alti or Lati) separating populations. We showed previously that all populations along a single valley stem from a unique source population and that secondary contact can be excluded (Alberto et al 2010). The comparison of clinal variation between two biological replicates (two valleys) can be used to determine the surfing effect.…”

“…We performed 50,000 coalescent simulations of 50 groups, with 100 demes per group. The populations from the latitudinal gradient formed three groups on the basis of chloroplast haplotypes, but we did not analyze the populations of the altitudinal gradients as they were known to belong, essentially, to a single chloroplast lineage (Alberto et al 2010; Table 1). The detection of F ST outlier SNPs was therefore based on BayeScan results for the altitudinal gradient and BayeScan and Arlequin results for the latitudinal gradient.…”

“…Five randomized complete blocks were set up in a 3.5-to 1.5-m density plantation (see Alberto et al 2011 for details). Two additional populations (L4 and L14) were also used for the detection of molecular signatures of selection, resulting in the sample of 12 populations in total for molecular analyses (see Alberto et al 2010 for details). Petit et al (2002), Kremer et al (2002), and Alberto et al (2010).…”

“…For the altitudinal gradient, buds or leaves were harvested from 9-43 adult trees from each population in situ (see Alberto et al 2010 for details), for the female parents of the offspring installed in the combined provenance and progeny tests.…”