Amphitropical variation of the algal partners of Pseudephebe (Parmeliaceae, lichenized fungi)

Abstract

Lichens are present in most terrestrial ecosystems on Earth and colonize extreme habitats, where vascular plants are unable to thrive, due to unique properties of the fungal-algal symbiosis. Here, we explored the phylogeographic structure of green algae engaged in symbiosis with species in the genus Pseudephebe (Parmeliaceae). These often form deep brown to blackish fruticose thalli on acidic rocks, and have partially overlapping distributions: P. minuscula is bipolar and co-occurs with P. pubescens in Europe. Based on a broad sampling, including the Arctic and Antarctica, we focused on photobionts (1) to identify genetic lineages and their phylogenetic assignment, (2) to infer the haplotype distribution in relation with geography and the mycobiont's identity, and (3) to evaluate spatial genetic structure and polymorphism. Results revealed three Trebouxia clade S lineages (Trebouxia S02, T. suecica and T. angustilobata) associated to Pseudephebe species, with predominant haplotypes distributed throughout the entire geographic distribution, and some, less frequent, shared between widely distant localities. Photobiont switching was evident in the Mediterranean region, and algal co-occurrence was frequent in both mycobionts, which shared the same set of photobionts; this could explain, at least partially, their overlapping distribution. Furthermore, genetic structure was influenced by geography given the substantial percentages of genetic variation (ca. 25-50%) explained by the different delimited eco−/biogeographic regions. In Continental Antarctica, mycobionts showed a high specialization towards the photobionts, which are probably endemic of this climatically extreme region. Taken together, our findings provide further insight about the processes shaping lichen biogeography.

Photobiont Diversity in Lichen Symbioses From Extreme Environments

“…Of these, only two thalli came from a mountain massif in Spain, while all the other samples were collected on the Italian Alps. Trebouxia belonging to clade “S” and more specifically to the T. simplex and Trebouxia “S02” lineages have already been documented in Alpine lichens ( Blaha et al, 2006 ; Garrido-Benavent et al, 2020 ) and have been previously reported for T. atra as well ( Muggia et al, 2010 , 2014a ). Although not restricted to the Alps, both T. simplex and Trebouxia “S02” have been reported from lichen symbioses from cold and rather humid areas, and our survey seems to confirm once again their ecological preferences.…”

Unravelling the Symbiotic Microalgal Diversity in Buellia zoharyi (Lichenized Ascomycota) from the Iberian Peninsula and Balearic Islands Using DNA Metabarcoding

“…Furthermore, the association with a wide range of symbionts, including locally adapted photobiont strains, has been hypothesized as a driver of lichenized fungal evolution [25,26]. Although the photobiont adaptive hypothesis has only been occasionally experimentally tested in lichens [24,27], several studies have shown a strong correlation between the photobiont genotype and the geographical and ecological distribution of the lichen [23,[28][29][30][31][32].…”

Phylogeny and Ecology of Trebouxia Photobionts From Bolivian Lichens

“…Interestingly, the exception in clade S is Trebouxia sp. S10, which is known to occur also in the Mediterranean ( Sadowska-Deś et al, 2013 ) and the Neotropical climate (Costa Rica— Nelsen and Gargas, 2009 ; Bolivia— Garrido-Benavent et al, 2020 ).…”

“…To reveal the structure of the Bolivian photobiont pattern, we analyzed its relationship with the lichen genus or family and assessed the comparative effects of climate, altitude, geographical distances, substrate, and habitat type, as well as thallus type, propagation mode, and secondary metabolites composition. Variation partitioning analysis was carried on the ITS database separately for all Bolivian data obtained in this study ( N = 408 and additional four from Garrido-Benavent et al, 2020 ). Additionally, using all Trebouxia sequences available in GenBank, we applied several variation partitioning analyses on different datasets: all available data ( N = 2,880), Clade A ( N = 1,080), Clade C ( N = 347), Clade I ( N = 381), and Clade S ( N = 1,072).…”