Phylogeny and Ecology of Trebouxia Photobionts From Bolivian Lichens

High Andean Steppes of Southern Chile Contain Little-Explored Peltigera Lichen Symbionts

Peltigera lichens can colonize extreme habitats, such as high-elevation ecosystems, but their biodiversity is still largely unknown in these environments, especially in the southern hemi- sphere. We assessed the genetic diversity of mycobionts and cyanobionts of 60 Peltigera lichens collected in three high Andean steppes of southern Chile using LSU, β-tubulin, COR3 and ITS loci for mycobionts, and SSU and rbcLX loci for cyanobionts. We obtained 240 sequences for the different mycobiont markers and 118 for the cyanobiont markers, including the first report of β-tubulin sequences of P. patagonica through modifying a previously designed primer. Phylogenetic analyses, ITS scrutiny and variability of haplotypes were used to compare the sequences with those previously reported. We found seven mycobiont species and eleven cyanobiont haplotypes, including considerable novel symbionts. This was reflected by ~30% of mycobionts and ~20% of cyanobionts haplotypes that yielded less than 99% BLASTn sequence identity, 15 new sequences of the ITS1-HR, and a putative new Peltigera species associated with 3 Nostoc haplotypes not previously reported. Our results suggest that high Andean steppe ecosystems are habitats of unknown or little-explored lichen species and thus valuable environments to enhance our understanding of global Peltigera biodiversity.

Phylogeography of Ramalina farinacea (Lichenized Fungi, Ascomycota) in the Mediterranean Basin, Europe, and Macaronesia

Ramalina farinacea is an epiphytic lichen-forming fungus with a broad geographic distribution, especially in the Northern Hemisphere. In the eighties of the last century, it was hypothesized that R. farinacea had originated in the Macaronesian–Mediterranean region, with the Canary Islands as its probable southernmost limit, and thereafter it would have increased its distribution area. In order to explore the phylogeography of this emblematic lichen, we analyzed 120 thalli of R. farinacea collected in 38 localities distributed in temperate and boreal Europe, the Western Mediterranean Basin, and several Macaronesian archipelagos in the Atlantic Ocean. Data from two nuclear markers (nrITS and uid70) of the mycobiont were obtained to calculate genetic diversity indices to infer the phylogenies and haplotype networks and to investigate population structure. In addition, dating analysis was conducted to provide a valuable hypothesis of the timing of the origin and diversification of R. farinacea and its close allies. Our results highlight that phylogenetic species circumscription in the “Ramalina farinacea group” is complex and suggests that incomplete lineage sorting is at the base of conflicting phylogenetic signals. The existence of a high number of haplotypes restricted to the Macaronesian region, together with the diversification of R. farinacea in the Pleistocene, suggests that this species and its closest relatives originated during relatively recent geological times and then expanded its range to higher latitudes. However, our data cannot rule out whether the species originated from the Macaronesian archipelagos exclusively or also from the Mediterranean Basin. In conclusion, the present work provides a valuable biogeographical hypothesis for disentangling the evolution of this epiphytic lichen in space and time.

Trebouxia lynnae sp. nov. (Former Trebouxia sp. TR9): Biology and Biogeography of an Epitome Lichen Symbiotic Microalga

Two microalgal species, Trebouxia jamesii and Trebouxia sp. TR9, were detected as the main photobionts coexisting in the thalli of the lichen Ramalina farinacea. Trebouxia sp. TR9 emerged as a new taxon in lichen symbioses and was successfully isolated and propagated in in vitro culture and thoroughly investigated. Several years of research have confirmed the taxon Trebouxia sp. TR9 to be a model/reference organism for studying mycobiont−photobiont association patterns in lichen symbioses. Trebouxia sp. TR9 is the first symbiotic, lichen-forming microalga for which an exhaustive characterization of cellular ultrastructure, physiological traits, genetic and genomic diversity is available. The cellular ultrastructure was studied by light, electron and confocal microscopy; physiological traits were studied as responses to different abiotic stresses. The genetic diversity was previously analyzed at both the nuclear and organelle levels by using chloroplast, mitochondrial, and nuclear genome data, and a multiplicity of phylogenetic analyses were carried out to study its intraspecific diversity at a biogeographical level and its specificity association patterns with the mycobiont. Here, Trebouxia sp. TR9 is formally described by applying an integrative taxonomic approach and is presented to science as Trebouxia lynnae, in honor of Lynn Margulis, who was the primary modern proponent for the significance of symbiosis in evolution. The complete set of analyses that were carried out for its characterization is provided.