Novel Insights Into Refugia at the Southern Margin of the Distribution Range of the Endangered Species Ulmus laevis.

Sara Torre,Alberto Selvaggi,Alessia L Pepori,Francesco Pecori,Iacopo Passeri,Alberto Santini,Luisa Ghelardini,Federico Sebastiani,Guia Burbui

doi:10.3389/fpls.2022.826158

Abstract

Riparian ecosystems, in long-time developed regions, are among the most heavily impacted by human activities; therefore, the distribution of tree riparian species, such as Ulmus laevis, is highly affected. This phenomenon is particularly relevant at the margins of the natural habitat of the species, where populations are small and rare. In these cases, it is difficult to distinguish between relics or introductions, but it is relevant for the restoration of natural habitats and conservation strategies. The aim of this study was to study the phylogeography of the southern distribution of the species. We sequenced the entire chloroplast (cp) genomes of 54 individuals from five sampled populations across different European regions to highlight polymorphisms and analyze their distribution. Thirty-two haplotypes were identified. All the sampled populations showed private haplotypes that can be considered an indicator of long-term residency, given the low mutation rate of organellar DNA. The network of all haplotypes showed a star-like topology, and Serbian haplotypes were present in all branches. The Balkan population showed the highest level of nucleotide and genetic diversity. Low genetic differentiation between populations was observed but we found a significant differentiation among Serbia vs. other provenances. Our estimates of divergent time of U. laevis samples highlight the early split of above all Serbian individuals from other populations, emphasizing the reservoir role of white elm genetic diversity of Serbian population.

Highlights

Modern biodiversity conservation strategies rely, or at least should, on the knowledge of genetic resources (Gepts, 2006; Hoban et al, 2021)
The cpDNA had a size of 159,086 bp, had a guanine-cytosine (GC) content of 35.6%, and its map had the typical quadripartite structure of angiosperms, including two inverted repeats (IRs) of 26,424 bp separated by a large single copy (LSC) of 87,594 bp and a small single copy (SSC) of 18,644 bp (Figure 1)
The dataset was reduced to 54 cp genomes: samples U29 and U35 (Supplementary Table 1) were the same sample sequenced twice as well as sample U42 was sequenced twice as control for the sequencing process, as expected we obtained the same haplotypes from replicated samples

Summary

Introduction

Modern biodiversity conservation strategies rely, or at least should, on the knowledge of genetic resources (Gepts, 2006; Hoban et al, 2021). Porth and El-Kassaby, 2014), exploring the geographical distribution and structure of genetic diversity and describing the patterns of reduction and expansion of populations mainly related to glaciation and recolonization, respectively (Petit et al, 2003; Heuertz et al, 2004; Mona et al, 2010; Lanier et al, 2015). The picture that came out progressively gained complexity by considering the effect of preglacial variation distribution (Magri, 2008) and the existence of extra-Mediterranean refugia (Pedreschi et al, 2019). Despite these huge efforts, there are still species that are highly impacted by anthropogenic activity and by pests whose distribution is poorly investigated and that could represent a priority for habitat restoration

Objectives

Methods

Results

Conclusion