Abstract
All fungi in the class Lichinomycetes are lichen-forming and exclusively associate with cyanobacteria. Two closely related maritime species of the genus Lichina (L. confinis and L. pygmaea) show similar distribution ranges in the Northeast Atlantic, commonly co-occurring at the same rocky shores but occupying different littoral zones. By means of 16S rRNA and phycocyanin operon markers we studied a) the phylogenetic relationships of cyanobionts associated with these species, b) the match of divergence times between both symbionts, and c) whether Lichina species differ in photobiont association and in how geography and ecology affect selectivity. The cyanobionts studied are closely related to both marine and freshwater strains of the genus Rivularia. We found evidence of a high specificity to particular cyanobiont lineages in both species: Lichina pygmaea and L. confinis incorporate specific lineages of Rivularia that do not overlap at the haplotype nor the OTU levels. Dating divergences of the fungal and cyanobacterial partners revealed an asynchronous origin of both lineages. Within each fungal species, selectivity varied across the studied area, influenced by environmental conditions (both atmospheric and marine), although patterns were highly correlated between both lichen taxa. Ecological speciation due to the differential association of photobionts to each littoral zone is suspected to have occurred in marine Lichina.
Highlights
Cyanobacteria are key components of ecosystems across Earth since the great oxygenation event (2.45–2.32 billion years ago) [1]
The specimens of L. pygmaea collected in the Canary Islands are not congruent with the other specimens both morphologically and genetically, suggesting the presence of an undescribed taxon in the region which we will tentatively address here as Lichina ‘canariensis’ pending a complete taxonomic treatment of the taxon to be further developed in a later article
The final dataset of the phycocyanin operon comprises 205 specimens, 91 of which were sequenced from L. pygmaea, 94 from L. confinis, 18 from L. ‘canariensis’, and two from free-living cyanobacterial colonies
Summary
Cyanobacteria are key components of ecosystems across Earth since the great oxygenation event (2.45–2.32 billion years ago) [1]. In addition to playing an important role in basic ecosystem processes, such as nutrient cycling and nitrogen fixation [2], they have contributed to the development and diversification of eukaryotic life. Ecological Specialization in Two Closely Related Cyanolichens. Biosfera Consultoría Medioambiental provided support in the form of a salary for author ATB, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of all authors are articulated in the ‘author contributions’ section
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