Evolution of cyanobacterial symbioses in Ascomycota

Two-fifths of the species in Ascomycota are lichen-forming, of which 10% and 3-4% have cyanobacteria as the primary and secondary photobionts respectively. To study the evolution of cyanobacterial symbioses, the phylogenetic relationships within the Ascomycota have been reconstructed. Phylogenetic analyses were made using direct optimization of nuclear SSU and LSU rDNA sequences under the parsimony optimality criterion. Our results indicate repeated evolution of the mutualistic assemblages between fungi and cyanobacteria. The stability of the cyanobacterial symbioses and the effects of photobiont alteration on the evolution of ascomycetes are discussed, as is the taxonomy of some cyanobacterial lichen taxa and some future perspectives on the evolution of these ecologically important assemblages.