Patterns of polymorphism resulting from long‐range colonization in the Mediterranean conifer Aleppo pine

Abstract

Summary• The evolutionary outcomes of range expansion ⁄ contraction depend on the biological system considered and the interactions among the evolutionary forces in place. In this study, we examined the demographic history and the local polymorphism patterns of candidate genes linked to drought tolerance of a widespread Mediterranean conifer (Pinus halepensis).• To that end, we used cpSSRs and coalescence modelling of nuclear genes to infer the demographic history of natural populations covering the species range. Ten drought-response candidate genes were then examined for their patterns of polymorphism and tested for selection considering plausible demographic scenarios.• Our results revealed a marked loss of genetic diversity from the relictual Greek population towards the western range of the species, as well as molecular signatures of intense bottlenecks. Moreover, we found an excess of derived polymorphisms in several genes sampled in the western part of the range -a potential result of the action of natural selection on populations confronted with new environments following long-range colonization.• Wide-range expansions-contractions of forest trees are accompanied by strong selective pressures, resulting in distinct evolutionary units. This knowledge is of crucial importance for the conservation and management of forests in the face of climate change.

High genetic diversity at the extreme range edge: nucleotide variation at nuclear loci in Scots pine (Pinus sylvestris L.) in Scotland

“…In our data, coalescent simulation of various demographic scenarios supported the conclusion that bottlenecking had occurred, but suggested more recent timing. A similar signal, suggesting bottlenecking on a timescale related to the most recent glaciation, was detected in Italian populations of Aleppo pine (Grivet et al, 2009). Furthermore, the severity of the bottleneck experienced by Scottish populations appears to have been strong enough to account for the observed discrepancy in allelic frequency distributions and decay of LD, in contrast to continental European tree populations (Lascoux et al, 2008).…”

“…Reduced decay of LD has also been observed in populations of American P. taeda that had probably experienced bottlenecks (Brown et al, 2004;González-Martínez et al, 2006a) and contrasting allele frequency distributions were observed between northern populations and recently bottlenecked southern populations of Quercus crispula in Japan (where the latter showed positive Tajima's D, Quang et al, 2008). Although there are exceptions (Grivet et al, 2009), it is expected that bottlenecks should have a stronger impact on the allele frequency distribution spectrum and LD than on the overall level of diversity . Long-lived, wind-pollinated tree species should be capable of maintaining genetic diversity even during range shifts; that is, they are buffered against rapid changes in genetic variation due to fluctuations in population size (Austerlitz et al, 2000).…”

Population at the edge: increased divergence but not inbreeding towards northern range limit in Acer campestre

“…This kind of spatial pattern is generally found in tree species (e.g. Tollefsrud et al 2009;Grivet et al 2009), although such studies often require large spatial scales (Comps et al 2001;Coart et al 2005). This is because trees are often characterised by wide distribution, high potential for gene flow and strong human impact, including forest management and translocation of seed material (Petit and Hampe 2006).…”

“…For example, in many European trees the geographic distribution of genetic diversity reflects the process of postglacial recolonisation (Comps et al 2001;Coart et al 2005;Tollefsrud et al 2009;Grivet et al 2009). In consequence, genetic diversity tends to decrease with the distance from refugia (generally northwards), even if no sharp differences in a species' current density can be found.…”

Variation of early reproductive allocation in multi-site genetic trials of Maritime pine and Aleppo pine

“…Three different main gene pools have been differentiated (Bucci et al, 2007). On the other hand, Aleppo pine has a circunmediterranean distribution with genetically diverse populations in Greece and Turkey but more genetically uniform populations towards the west of the basin following a proposed colonization route (Grivet et al, 2009).…”