European phylogeography of the epiphytic lichen fungusLobaria pulmonariaand its green algal symbiont

Abstract

In lichen symbiosis, fungal and algal partners form close associations, often codispersed by vegetative propagules. Due to the particular interdependence, processes such as colonization, dispersal or genetic drift are expected to result in congruent patterns of genetic structure in the symbionts. To study the population structure of an obligate symbiotic system in Europe, we genotyped the fungal and algal symbionts of the epiphytic lichen Lobaria pulmonaria at eight and seven microsatellite loci, respectively, and analysed about 4300 L. pulmonaria thalli from 142 populations from the species' European distribution range. Based on a centroid approach, which localizes centres of genetic differentiation with a high frequency of geographically restricted alleles, we identified the South Italy-Balkan region as the primary glacial refugial area of the lichen symbiosis. Procrustean rotation analysis and a distance congruence test between the fungal and algal population graphs indicated general concordance between the phylogeographies of the symbionts. The incongruent patterns found in areas of postglacial recolonization may show the presence of an additional refugial area for the fungal symbiont, and the impact that horizontal photobiont transmission and different mutation rates of the symbionts have on their genotypic associations at a continental scale.

Genetic diversity of sterile culturedTrebouxiaphotobionts associated with the lichen-forming fungusXanthoria parietinavisualized with RAPD-PCR fingerprinting techniques

“…species of Trebouxia and clades of T. decolorans) and within a given algal lineage, and there was substantial differentiation between geographically distant sampling sites. Similar large-scale geographic trends have been found in various photobionts of lichen-forming ascomycetes (Yahr et al 2006;Wornik & Grube 2010;Fernández-Mendoza et al 2011;Widmer et al 2012).…”

Phylogeography of Alpine populations of Rhytidium rugosum (Bryophyta) in a European context

“…Extensive work exists for the lichenized fungus Lobaria pulmonaria (L.) Hoffm. and suggests immigration from glacial refugia in Southern Italy-Balkan, and potentially from additional refugia for the fungal component (Widmer et al 2012). Within the Alps, the presence of sexual reproduction in a specific L. pulmonaria population appears important to explain its genetic diversity (Zoller et al 1999).…”

High-Throughput Sequencing in Studies of Lichen Population Biology

“…On a landscape scale, climatic associations of fungal and algal gene pools have also been found for L. pulmonaria in the largest continuous primeval forest of Europe (Nadyeina et al 2014b). At the largest spatial scale, genetic differentiation of populations of L. pulmonaria mycobionts and photobionts has been shown within Europe and between continents Walser et al 2005;Widmer et al 2012).…”

“…Microsatellites are most useful for comparing closely related individuals and populations, although they have also in some cases been used to study populations situated on different continents, on a phylogeographic scale. The first microsatellite markers reported for lichens were developed for the mycobiont of Lobaria pulmonaria ; more recently, this method was also adopted for investigation of its green algal photobiont, Dictyochloropsis reticulata (Dal Grande et al 2009, 2012Widmer et al 2012). They offered a significant advantage over previous markers in providing a means by which a large number of individuals could be genotyped at a moderate cost per individual and have been employed successfully in studying genetic differentiation between populations and small-scale geographic variability within populations.…”