Abstract
Thamnolia is a lichenized fungus with an extremely wide distribution, being encountered in arctic and alpine environments in most continents. In this study, we used molecular markers to investigate the population structure of the fungal symbiont and the associated photosynthetic partner of Thamnolia. By analyzing molecular, morphological, and chemical variation among 253 specimens covering the species distribution range, we revealed the existence of three mycobiont lineages. One lineage (Lineage A) is confined to the tundra region of Siberia and the Aleutian Islands, a second (Lineage B) is found in the high alpine region of the Alps and the Carpathians Mountains, and a third (Lineage C) has a worldwide distribution and covers both the aforementioned ecosystems. Molecular dating analysis indicated that the split of the three lineages is older than the last glacial maximum, but the distribution ranges and the population genetic analyses suggest an influence of last glacial period on the present‐day population structure of each lineage. We found a very low diversity of Lineage B, but a higher and similar one in Lineages A and C. Demographic analyses suggested that Lineage C has its origin in the Northern Hemisphere, possibly Scandinavia, and that it has passed through a bottleneck followed by a recent population expansion. While all three lineages reproduce clonally, recombination tests suggest rare or past recombination in both Lineages A and C. Moreover, our data showed that Lineage C has a comparatively low photobiont specificity, being found associated with four widespread Trebouxia lineages (three of them also shared with other lichens), while Lineages A and B exclusively harbor T. simplex s. lat. Finally, we did not find support for the recognition of taxa in Thamnolia based on either morphological or chemical characters.
Highlights
Our understanding of how lichens colonize new habitats is still in its infancy, and studies including analyses of both main symbiotic partners are necessary to further understand their dispersal and ecological success
For the majority of the samples used in our investigation, we investigated field-collected thallus material, but for three of them axenic fungal cultures obtained from the Akita Prefectural University, Japan, or the Institute of Plant Sciences, University of Graz, Austria (Table S2), were used
Based on the genetic diversity estimates, we found that Lineage C and Lineage B contained the highest proportion of clones, while Lineage A exhibited a relatively low number of identical sequences (Table 1, Gdiv measurements)
Summary
Thallus fragmentation by lateral branches and longitudinal strips, containing an established, successful symbiotic partnership, has been assumed to be the main reproduction mode of Thamnolia (Andrei, Iacob, & Pascale, 2006– 2007; Lord et al, 2013). It is unknown whether the fragments travel long distances by wind alone, but it has been suggested that birds or grazing animals enable long-distance dispersal (Wright, 1992). The clonality of Thamnolia was supported when microsatellite (a)
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