Data from: Fungal specificity and selectivity for algae play a major role in determining lichen partnerships across diverse ecogeographic regions in the lichen-forming family Parmeliaceae

Microbial symbionts are instrumental to the ecological and long-term evolutionary success of their hosts, and the central role of symbiotic interactions is increasingly recognized across the vast majority of life. Lichens provide an iconic model for investigating patterns in species interactions, although relationships among lichen symbionts are often masked by uncertain species boundaries or inability to reliably identify symbionts. The species-rich lichen-forming fungal family Parmeliaceae provides a valuable system for assessing patterns of interactions of algal symbionts at various scales, and our study addresses patterns of lichen symbiont interactions at the largest geographical and taxonomical scales ever attempted. We analyzed a total of 2356 algal ITS sequences collected from lichens representing ten mycobiont genera in Parmeliaceae, two genera in Lecanoraceae, and 20 cultured Trebouxia strains. Algal sequences were grouped into operational taxonomic units (OTUs), and we explored patterns of symbiont interactions in these lichens based on ecogeographic distributions and mycobiont taxonomy. We found high levels of undescribed diversity in Trebouxia, broad distributions across distinct ecoregions for many photobiont OTUs, and varying levels of mycobiont selectivity and specificity towards the photobiont. Based on these results, we conclude that fungal specificity and selectivity for algal partners play a major role in determining lichen partnerships, potentially superseding ecology, at least at the ecogeographical scale investigated here. In order to facilitate effective communication and consistency across future studies, we propose a provisional naming system for Trebouxia photobionts and provide representative sequences for each OTU circumscribed in this study.