Major fungal lineages are derived from lichen symbiotic ancestors

Abstract

About one-fifth of all known extant fungal species form obligate symbiotic associations with green algae, cyanobacteria or with both photobionts. These symbioses, known as lichens, are one way for fungi to meet their requirement for carbohydrates. Lichens are widely believed to have arisen independently on several occasions, accounting for the high diversity and mixed occurrence of lichenized and non-lichenized (42 and 58%, respectively) fungal species within the Ascomycota. Depending on the taxonomic classification chosen, 15-18 orders of the Ascomycota include lichen-forming taxa, and 8-11 of these orders (representing about 60% of the Ascomycota species) contain both lichenized and non-lichenized species. Here we report a phylogenetic comparative analysis of the Ascomycota, a phylum that includes greater than 98% of known lichenized fungal species. Using a Bayesian phylogenetic tree sampling methodology combined with a statistical model of trait evolution, we take into account uncertainty about the phylogenetic tree and ancestral state reconstructions. Our results show that lichens evolved earlier than believed, and that gains of lichenization have been infrequent during Ascomycota evolution, but have been followed by multiple independent losses of the lichen symbiosis. As a consequence, major Ascomycota lineages of exclusively non-lichen-forming species are derived from lichen-forming ancestors. These species include taxa with important benefits and detriments to humans, such as Penicillium and Aspergillus.

Nephromyces, a beneficial apicomplexan symbiont in marine animals

“…Phylogenetic relatedness between pathogenic and mutualistic endosymbionts has been documented in several microbial clades. Among eukaryotic examples, ascomycete and basidiomycete fungi and dinoflagellates contain both mutualistic and parasitic symbionts, as well as freeliving species (34)(35)(36)(37). Bacteria provide several well-documented examples of especially close relatedness of mutualists and pathogens, including mutualistic and pathogenic members in Rhizobiaceae (38,39) and epsilonproteobacteria (40), and pathogenic and mutualistic species of the genera Burkholderia and Vibrio (41,42).…”

Negative feedback within a mutualism: host–specific growth of mycorrhizal fungi reduces plant benefit

“…These questions are of importance beyond the plant-AM fungal interaction, as they are equally relevant to the dynamics of other mutualisms (Bronstein 1994). Moreover, as the bene t that Plantago receives from its AM fungal community degrades over time, a microevolutionary process of this type could lead to the dissolution of the mutualism, as has been found to occur within several mutualisms over evolutionary time (Fitter & Moyersoen 1996;Hibbett et al 2000;Lutzoni et al 2001). Therefore, identifying what conditions lead to positive versus negative feedback represents an important step towards understanding the evolutionary maintenance of mutualism.…”

Primary biological aerosol particles in the atmosphere: a review

“…Nearly 20% of all known fungi species are lichenised (Lutzoni et al, 2001) and more than 98% of the lichenised fungi belong to Ascomycota and a few to Basidiomycota (Hawksworth et al, 1995;Tehler, 1996). Most of the lichenised fungi form symbioses with Chlorophyta, whereas only about 10% lichenise with cyanobacteria and 3% with both (Tschermal-Woess, 1988;Lewis and McCourt, 2004).…”