Insights into the ecology and genetics of lichens with a cyanobacterial photobiont
Abstract: Nature conservation requires an in-depth understanding of the ecological processes that influence species persistence in the different phases of a species life. In lichens, these phases comprise dispersal, establishment, and growth. This thesis aimed at increasing the knowledge on epiphytic cyanolichens by studying different aspects linked to these life stages, including species colonization extinction dynamics, survival and vitality of lichen transplants, and the genetic symbiont diversity in the genus Nephroma. Paper I reveals that local colonizations, stochastic, and deterministic extinctions occur in several epiphytic macrolichens. Species habitat-tracking metapopulation dynamics could partly be explained by habitat quality and size, spatial connectivity, and possibly facilitation by photobiont sharing. Simulations of species future persistence suggest stand-level extinction risk for some infrequent sexually dispersed species, especially when assuming low tree numbers and observed tree fall rates. Forestry practices influence the natural occurrence of species, and retention of trees at logging is one measure to maintain biodiversity. However, their long-term benefit for biodiversity is still discussed. The results of a 14-year transplantation study with the epiphytic Lobaria pulmonaria (paper IV) support the suitability of retention trees for species survival, especially if lichen thalli occur on north-facing sides. Lichens symbiotic nature requires the dispersal of both mycobiont and photobiont, which often occurs separately. Re-lichenization and symbiont selectivity are hence essential parts for lichen persistence. Using genetic markers, two papers (II & III) indicate that the 'choice' of the symbiotic partners in the genus Nephroma is not random, and that selectivity patterns vary between tree, local, and global scales. Particular symbiont associations are linked to geographical areas, and several lichen-forming fungi in Nephroma share tRNALeu (UAA) sequence-identical photobionts over a global scale. Relatively higher selectivity locally compared to globally indicated habitat preferences of particular symbiont combinations, but also a possible founder effect. While it still needs to be identified how and where lichen symbionts acquire their symbiotic partners, papers II and III support the idea that species form photobiont-sharing guilds, which possibly benefits their colonization success.
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