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

Abstract

Buellia zoharyi is a crustose placodioid lichen, usually occurring on biocrusts of semiarid ecosystems in circum-Mediterranean/Macaronesian areas. In previous work, we found that this lichenized fungus was flexible in its phycobiont choice in the Canary Islands. Here we test whether geography and habitat influence phycobiont diversity in populations of this lichen from the Iberian Peninsula and Balearic Islands using Sanger and high throughput sequencing (HTS). Additionally, three thallus section categories (central, middle and periphery) were analyzed to explore diversity of microalgal communities in each part. We found that B. zoharyi populations hosted at least three different Trebouxia spp., and this lichen can associate with distinct phycobiont strains in different habitats and geographic regions. This study also revealed that the Trebouxia composition of this lichen showed significant differences when comparing the Iberian Peninsula with the Balearics thalli. No support for differences in microalgal communities was found among thallus sections; however, several thalli showed different predominant Trebouxia spp. at each section. This result corroborate that thallus parts selected for DNA extraction in metabarcoding analyses are key to not bias the total phycobiont diversity detected. This study highlights that inclusion of HTS analysis is crucial to understand lichen symbiotic microalgal diversity.

Biodiversity Patterns and Ecological Preferences of the Photobionts Associated With the Lichen-Forming Genus Parmelia

“…As mentioned in the introduction, Trebouxia spp. tended to form five well-supported monophyletic clades: A, C, I, S, and D. According to this accepted Trebouxia clade code (Leavitt et al, 2015;Moya et al, 2017Moya et al, , 2021Muggia et al, 2020;Xu et al, 2020), all sequences generated in this study belong exclusively to clades S and I. LSU rDNA phylogeny corroborated the Trebouxia assignment at clade level (S and I), but showed less resolution at a species level (Supplementary Figure 2).…”

“…In general, it has been shown that species with worldwide distributions associate with a wide phycobiont range (Blaha et al, 2006;Muggia et al, 2014;Moya et al, 2017), while species growing in restricted areas are more specific (Otálora et al, 2010(Otálora et al, , 2013Leavitt et al, 2016;Magain et al, 2017). However, there are exceptions to this rule, such as gypsum lichen species which colonized very restricted areas, but showed high flexibility in their phycobiont choice (Moya et al, 2021). Some species of Parmelia included in this study have broad geographical and ecological distribution ranges.…”

“…Piercey-Normore (2004) pointed out these factors to explain the association myco/phycobiont patterns in Cladonia. More recently, Moya et al (2017Moya et al ( , 2021 and Molins et al (2021) underlined that different thallus parts of crustose or fruticulose lichen species could harbor different microalgal compositions. Also, Leavitt et al (2015) highlighted evidence of the correlation between thalli growth forms and selectivity in Parmeliaceae mycobionts.…”

“…Lichen thalli were processed as described in Moya et al (2021), in brief: specimens were examined under a stereo microscope to remove surface contamination (mainly tree bark). Selected fragments from different parts of each thallus were randomly excised and pooled together.…”

“…8% of the surface of the planet (Nash, 2008). However, phycobiont distribution patterns seem to show their own ecological preferences, independently of the lichen forming fungus (Peksa and Škaloud, 2011;Řídká et al, 2014;Rolshausen et al, 2020;Moya et al, 2021). In fact, both restricted and globally distributed phycobionts have been recorded (Muggia et al, 2014;Vančurová et al, 2018;Garrido-Benavent et al, 2021).…”