So you've got your fungus and your algae (or cyanobacteria) (and the multitude of other variations and additions to this two-species symbiosis that lichens present). Do the species that comprise the lichen communicate with each other via chemical or electrical signalling? For instance, could an algal cell "tell" the fungus that it's diseased, thus triggering the allocation of more resources toward pathogen resistance?
And if there is no communication, how have lichens been so successful?