title: Fungal specificity and selectivity for algae play a major role in determining lichen partnerships across diverse ecogeographic regions in the lichen-forming family Parmeliaceae (Ascomycota).
abstract: Microbial symbionts are instrumental to the ecological and long-term evolutionary success of their hosts, and the central role of symbiotic interactions is increasingly recognized across the vast majority of life. Lichens provide an iconic group for investigating patterns in species interactions; however, relationships among lichen symbionts are often masked by uncertain species boundaries or an inability to reliably identify symbionts. The species-rich lichen-forming fungal family Parmeliaceae provides a diverse group for assessing patterns of interactions of algal symbionts, and our study addresses patterns of lichen symbiont interactions at the largest geographic and taxonomic scales attempted to date. We analysed a total of 2356 algal internal transcribed spacer (ITS) region sequences collected from lichens representing ten mycobiont genera in Parmeliaceae, two genera in Lecanoraceae and 26 cultured Trebouxia strains. Algal ITS sequences were grouped into operational taxonomic units (OTUs); we attempted to validate the evolutionary independence of a subset of the inferred OTUs using chloroplast and mitochondrial loci. We explored the patterns of symbiont interactions in these lichens based on ecogeographic distributions and mycobiont taxonomy. We found high levels of undescribed diversity in Trebouxia, broad distributions across distinct ecoregions for many photobiont OTUs and varying levels of mycobiont selectivity and specificity towards the photobiont. Based on these results, we conclude that fungal specificity and selectivity for algal partners play a major role in determining lichen partnerships, potentially superseding ecology, at least at the ecogeographic scale investigated here. To facilitate effective communication and consistency across future studies, we propose a provisional naming system for Trebouxia photobionts and provide representative sequences for each OTU circumscribed in this study.
authors.affiliation: Committee on Evolutionary Biology, University of Chicago, Chicago, IL, USA.|Science & Education, The Field Museum, Chicago, IL, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Leavitt
authors.affiliation: Science & Education, The Field Museum, Chicago, IL, USA.|Department of Botany, Faculty of Science, Kasetsart University, Bangkok, Thailand.
authors.forename: Ekaphan
authors.initials: E
authors.lastname: Kraichak
authors.affiliation: Geological and Environmental Sciences, Stanford University, Stanford, CA, USA.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Nelsen
authors.affiliation: Biology Department, Whitman College, Walla Walla, WA, USA.
authors.forename: Susanne
authors.initials: S
authors.lastname: Altermann
authors.affiliation: Departamento de Biología Vegetal II, Facultad de Farmacia, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Divakar
authors.affiliation: Departamento de Biología Vegetal II, Facultad de Farmacia, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Alors
authors.affiliation: Department of Biological Sciences, North Dakota State University, Fargo, ND, USA.
authors.forename: Theodore L
authors.initials: TL
authors.lastname: Esslinger
authors.affiliation: Departamento de Biología Vegetal II, Facultad de Farmacia, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Crespo
authors.affiliation: Science & Education, The Field Museum, Chicago, IL, USA.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Lumbsch
mesh_terms: D005075:Biological Evolution; D000460:Chlorophyta / Q000145:classification* / Q000235:genetics; D048028:DNA, Algal / Q000235:genetics; D018742:DNA, Chloroplast / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D017753:Ecosystem; D005658:Fungi / Q000235:genetics; D005843:Geography; D008011:Lichens / Q000382:microbiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013559:Symbiosis
chemical_list: D048028:DNA, Algal; D018742:DNA, Chloroplast; D004272:DNA, Mitochondrial; D021903:DNA, Ribosomal Spacer
keywords: Trebouxia; co-evolution; ecology; ecoregion; mycobiont; photobiont