High Genetic Diversity and Distinctiveness of Rear-Edge Climate Relicts Maintained by Ancient Tetraploidisation for Alnus glutinosa

Abstract

Populations located at the rear-edge of a species’ distribution may have disproportionate ecological and evolutionary importance for biodiversity conservation in a changing global environment. Yet genetic studies of such populations remain rare. This study investigates the evolutionary history of North-African low latitude marginal populations of Alnus glutinosa Gaertn., a European tree species that plays a significant ecological role as a keystone of riparian ecosystems. We genotyped 551 adults from 19 populations located across North Africa at 12 microsatellite loci and applied a coalescent-based simulation approach to reconstruct the demographic and evolutionary history of these populations. Surprisingly, Moroccan trees were tetraploids demonstrating a strong distinctiveness of these populations within a species otherwise known as diploid. Best-fitting models of demographic reconstruction revealed the relict nature of Moroccan populations that were found to have withstood past climate change events and to be much older than Algerian and Tunisian populations. This study highlights the complex demographic history that can be encountered in rear-edge distribution margins that here consist of both old stable climate relict and more recent populations, distinctively diverse genetically both quantitatively and qualitatively. We emphasize the high evolutionary and conservation value of marginal rear-edge populations of a keystone riparian species in the context of on-going climate change in the Mediterranean region.

Genetic diversity and genetic structure of black alder (Alnus glutinosa [L.] Gaertn) in the Belgium-Luxembourg-France cross-border area

“…This model has recently been challenged by a continentwide population genetic study (Havrdová et al 2015), suggesting that multiple refugia served as sources for the postglacial colonization of Europe by A. glutinosa, central Europe being an area of genetic admixture between western and eastern lineages originating from the northern part of the Iberian Peninsula and the Carpathians, respectively. Using SSR markers, Lepais et al (2013) showed a strong distinctiveness of Moroccan populations of A. glutinosa in the rear-edge distribution margins of the species. Recently, two studies using SSR markers have shown high levels of genetic diversity and very little differentiation between Irish A. glutinosa populations (Beatty et al 2015;Cubry et al 2015).…”

Landscape genomics and a common garden trial reveal adaptive differentiation to temperature across Europe in the tree species Alnus glutinosa

“…Moreover, ancient tetraploidization probably allowed the species to maintain high genetic diversity and adaptability in the rear‐edge climate relicts of northern Africa, by increasing the effective population size, which further corroborates the adaptive potential of the species (Lepais et al . ). A previous landscape genetic study based on 163 AFLP markers already suggested a signal of adaptation to climate conditions in Europe (Cox et al .…”

Alder and the Golden Fleece: high diversity of Frankia and ectomycorrhizal fungi revealed from Alnus glutinosa subsp. barbata roots close to a Tertiary and glacial refugium

“…More recently, the existence of both refugia in Belarus and western Russia has been demonstrated; they were important sources for northward post-glacial expansion of alders (Douda et al, 2014). Today, A. glutinosa populations are still marked by recent isolation in glacial refugia (King & Ferris, 1998), and several unique chloroplast haplotypes have been detected in relict populations from Morocco (Lepais et al, 2013) and Turkey (King & Ferris, 1998; Havrdová et al, 2015). Of interest, the high genetic diversity detected in Turkey concurs with the observed morphological variations of A. glutinosa in this region.…”