Genetic Structure in the Northern Range Margins of Common Ash, Fraxinus excelsior L.

Abstract

During post glacial colonization, loss of genetic diversity due to leading edge effects may be attenuated in forest trees because of their prolonged juvenile phase, allowing many migrants to reach the colonizing front before populations become reproductive. The northern range margins of temperate tree taxa in Europe are particularly suitable to study the genetic processes that follow colonization because they have been little affected by northern refugia. Here we examined how post glacial range dynamics have shaped the genetic structure of common ash (Fraxinus excelsior L.) in its northern range compared to its central range in Europe. We used four chloroplast and six nuclear microsatellites to screen 42 populations (1099 trees), half of which corresponded to newly sampled populations in the northern range and half of which represented reference populations from the central range obtained from previously studies. We found that northern range populations of common ash have the same chloroplast haplotypes as south-eastern European populations, suggesting that colonization of the northern range took place along a single migration route, a result confirmed by the structure at the nuclear microsatellites. Along this route, diversity strongly decreased only in the northern range, concomitantly with increasing population differentiation and complex population substructures, a pattern consistent with a leading edge colonization model. Our study highlights that while diversity is maintained in the central range of common ash due to broad colonizing fronts and high levels of gene flow, it profoundly decreases in the northern range, where colonization was unidirectional and probably involved repeated founder events and population fluctuations. Currently, common ash is threatened by ash dieback, and our results on northern populations will be valuable for developing gene conservation strategies.

Analysis of DNA profiles of ash (Fraxinus excelsior L.) to provide evidence of illegal logging

“…The mean heterozygosity level obtained for 287 Polish ash trees for the nuclear markers (H E = 0.857) was similar to 0.871 reported by Tollefsrud et al (2016) for the same set of markers used to assess 1099 ashes sampled across Europe. Further, Ruņģis et al (2016) reported similar genetic variation for Lithuanian ash trees examined with five Femsatl4, Femsatl10, Femsatl16, Femsatl19 and M2-30 loci.…”

“…Those samples were preselected based on mechanoscopy hint (very likely match). The molecular marker set applied to this case study has previously been proven to be highly polymorphic in population-level study of F. excelsior in Europe (Sutherland et al 2010;Tollefsrud et al 2016).…”

Demographic, Taxonomic, and Genetic Characterization of the Snook Species Complex (Centropomus spp.) along the Leading Edge of Its Range in the Northwestern Gulf of Mexico

“…; Tollefsrud et al. ). Second, the demographic data reported here suggest persistent expansion and contraction of snook in Texas, and these pulses of abundance at the edge of the species’ range can be expected to be coupled with complementary pulses of gene flow.…”

“…The patchiness pattern observed in microsatellite data could be further reinforced by multiple factors associated with the distribution of snook species at the edge of their population ranges. First, Texas represents the leading northern edge of the snook species' range in the western Gulf of Mexico, and previous studies on population leading edges have also observed patterns of disorganized but significant genetic divergence over small spatial scales (Eschbach et al 2014;Shirk et al 2014;Hagen et al 2015;Tollefsrud et al 2016). Second, the demographic data reported here suggest persistent expansion and contraction of snook in Texas, and these pulses of abundance at the edge of the species' range can be expected to be coupled with complementary pulses of gene flow.…”

Effect of fungal pathogens and climatic factors on production, biodiversity and health status of ash mountain forests

“…European ash (Fraxinus excelsior L.) is an important tree species in Europe and a great part of Asia (Kerr & Cahalan, 2004;Fraxigen, 2005;Tollefsrud et al, 2016). Fraxinus is a flexible genus which can be found over a wide range of growing conditionsfrom coastal to mountainous regions, especially on steep slopes (Stöhr & Lösch, 2004), from pioneer to mature woodland, from nutrient-rich to poorer soils (Ferrazzini et al, 2007;Dufour & Piégay, 2008).…”