Abstract
In this study, we explored the diversity of green algal symbionts (photobionts) in sympatric populations of the cosmopolitan lichen-forming fungi Thamnolia and Cetraria. We sequenced with both Sanger and Ion Torrent High-Throughput Sequencing technologies the photobiont ITS-region of 30 lichen thalli from two islands: Iceland and Öland. While Sanger recovered just one photobiont genotype from each thallus, the Ion Torrent data recovered 10–18 OTUs for each pool of 5 lichen thalli, suggesting that individual lichens can contain heterogeneous photobiont populations. Both methods showed evidence for photobiont sharing between Thamnolia and Cetraria on Iceland. In contrast, our data suggest that on Öland the two mycobionts associate with distinct photobiont communities, with few shared OTUs revealed by Ion Torrent sequencing. Furthermore, by comparing our sequences with public data, we identified closely related photobionts from geographically distant localities. Taken together, we suggest that the photobiont composition in Thamnolia and Cetraria results from both photobiont-mycobiont codispersal and local acquisition during mycobiont establishment and/or lichen growth. We hypothesize that this is a successful strategy for lichens to be flexible in the use of the most adapted photobiont for the environment.
Highlights
Symbiosis is any type of close and long-term biological interaction between at least two different organisms
We investigated the diversity of photobionts in sympatric populations of Thamnolia and Cetraria from two geographic localities (Iceland and Öland)
We investigated whether the retrieved local photobiont genotypes can be encountered in Thamnolia and Cetraria individuals from other parts of the world
Summary
Symbiosis is any type of close and long-term biological interaction between at least two different organisms. Across the Tree of Life, there are numerous examples of independently arisen symbiotic interactions with similar ecological and/or morphological outcomes[1] among which lichens and reef corals being representative examples These long-lived symbiotic entities are formed by heterotrophic organisms, fungi or animals, which acquire their carbon from the autotrophic microbes. It was shown that photobiont genotypes can be shared by diverse mycobionts at the same location[17,19,20,21,22,23,24,25,26,27,28,29,30] All of these findings advocate that lichen forming fungi associate with local adapted photobiont strains that will be selected and increase in frequency within population[19]. This study increases our understanding of the nature of symbioses formed by heterotrophs and autotrophs, and may spur other researchers to use HTS methodology to examine the photobiont community of lichens
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