Ecological and evolutionary role of photobiont-mediated guilds in lichens

Lichens have arisen independently on several occasions and there have also been multiple losses of the lichen symbiosis in different fungal lineages. This pluralistic evolutionary history explains major patterns in the current diversity of lichens and the mixed occurrences of lichenized and non-lichenized species in many fungal groups. However, we still have an insufficient understanding of factors that induce re- and de-lichenization events and. promote phylogenetic change in lichen symbionts over evolutionary time. While lichens are often cited as one classic example of coevolution, reciprocal evolutionary change between symbionts has been difficult to demonstrate. The apparent lack of phylogenetic tracking in many lichen groups indicates that a broader context is needed in which to interpret coevolution. This article provides some elements for such a framework and argues that the present diversity of lichen symbionts has evolved within an ecological kaleidoscope of photobiont-mediated guilds.