Contrasting patterns of historical colonization in white oaks (Quercusspp.) in California and Europe

Abstract

Phylogeography allows the inference of evolutionary processes that have shaped the current distribution of genealogical lineages across a landscape. In this perspective, comparative phylogeographical analyses are useful in detecting common historical patterns by either comparing different species within the same area within a continent or by comparing similar species in different areas. Here, we analyse one taxon (the white oak, genus Quercus, subgenus Quercus, section Quercus) that is widespread worldwide, and we evaluate its phylogeographical pattern on two different continents: western North America and Western Europe. The goals of the present study are: (i) to compare the chloroplast genetic diversity found in one California oak species vs. that found in the extensively studied European oak species (in France and the Iberian Peninsula); (ii) to contrast the geographical structure of haplotypes between these two taxa and test for a phylogeographical structure for the California species. For this purpose, we used the same six maternally inherited chloroplast microsatellite markers and a similar sampling strategy. The haplotype diversity within site as well as the differentiation among sites was alike in both taxa, but the Californian species has higher allelic richness with a greater number of haplotypes (39 vs. 11 in the European white oak complex). Furthermore, in California these 39 haplotypes are distributed locally in patches while in the European oaks haplotypes are distributed into lineages partitioned longitudinally. These contrasted patterns could indicate that gene movement in California oak populations have been more stable in response to past climatic and geological events, in contrast to their European counterparts.

Population-level genetic variation and climate change in a biodiversity hotspot

“…The Mediterranean climate that became established by the mid-Pliocene in west central California and continued through the Pleistocene glaciations affected distributions of Quercus and associated species (Griffin, 1988). Genetic data support strong geographic structuring of populations within the species, determined to be about 200 km (Grivet et al, 2006); however, the genetic connectivity of current populations supports long-distance colonization (Sork et al, 2010). Combined with palynological data, these results suggest the Neogene was an important period for Quercus woodlands as they expanded and contracted with glaciations.…”

Phylogeography and climate-associated morphological variation in the endemic white oakQuercus deserticola(Fagaceae) along the Trans-Mexican Volcanic Belt

“…Most previous studies of oak species using cpDNA markers have found similar high differentiation levels and a clear geographic segregation of haplotypes lineages, which are usually explained by the historical migration patterns of the populations and the very low dispersal capacity of acorns (Magni et al 2005;Grivet et al 2006;Magri et al 2007;Marsico et al 2009). However, in Q. deserticola the distribution of haplotypes was rather patchy, displaying strong local genetic structure but without obvious phylogeographic breaks, contrasting with some previous studies in the TMVB that have found a west-east LGM, and the MIROC model suggested a modest eastwards expansion from the LGM to the present along the TMVB.…”

Population genetics of lichen-forming fungi – a review

“…For instance, most of California was not glaciated during the Pleistocene glacial and interglacial cycles. Accordingly, a recent phylogeographic study found much higher genetic variation in Californian than in European populations of white oaks, pointing towards California acting as a regional refugial area (Grivet et al 2006). Therefore, for European Letharia vulpina, at least one alternative hypothesis other than recent intercontinental dispersal seems plausible; old populations in Europe may have gone through profound genetic bottlenecks during the Pleistocene climatic oscillations, leading to their genetic depauperation.…”