Parallel evolution and phenotypic divergence in lichenized fungi: A case study in the lichen-forming fungal family Graphidaceae (Ascomycota: Lecanoromycetes: Ostropales)

Abstract

A molecular phylogeny of combined mtSSU, nuLSU, and RPB2 data revealed previously unrecognized levels of parallel evolution and phenotypic divergence in the lichen family Graphidaceae. Five clades were supported within the family: the Fissurina, Ocellularia, Graphis, Topeliopsis, and Thelotrema clades, containing 33 of the 42 currently accepted genera within the family. The results for the first time provide a fully resolved phylogeny of this family and confirm the synonymy of Graphidaceae and Thelotremataceae. Ancestral character state reconstruction using likelihood, Bayesian, and parsimony approaches indicate that lirellate ascomata evolved independently in each of the five clades. Carbonized ascomata evolved independently in at least four of the five clades. An unexpected result was the independent evolution of columella structures in the Fissurina and Ocellularia clades. Besides these more general findings, we document several cases in which evolution of several traits in parallel resulted in striking look-alikes within unrelated lineages, such as Topeliopsismuscigena and Chapsameridensis in the Topeliopsis and Thelotrema clades, Leptotremawightii, Myriotremalaeviusculum, and Leucodectonphaeosporum in the Ocellularia and Thelotrema clades, Ocellulariastylothecia and Melanotremameiosporum in the Fissurina and Ocellularia clades, and Myriotremapycnoporellum, Myriotremaclandestinum and Wirthiotremaglaucopallens in the Fissurina, Ocellularia, and Topeliopsis clades. Pagel’s test of independent character evolution suggested that at least for some of the traits involved in these cases, ecological constraints may have caused their evolution in parallel. The most intriguing find is the correlation between gall-forming thalli and vertical columns of calcium oxalate crystals, suggesting that these crystals do not function as light distributors, as previously assumed, but instead stabilize the thalli which are usually hollow beneath, similar to a dome-shaped structure. Ancestral character state reconstruction together with an approach to visualize the phenotype of putative ancestral lineages suggested the alpha-Graphidaceae to resemble some of the extant species currently classified in Myriotrema s.lat., with pore-like ascomata, and non-amyloid ascospores with lens-shaped lumina.