Genotype variability of Nostoc symbionts associated with three epiphytic Nephroma species in a boreal forest landscape

We studied lichen photobiont diversity patterns of three epiphytic Nephroma species in a 900-ha boreal forest landscape using cyanobacterial tRNA(Leu) (UAA) intron sequences. Our aim was to investigate if there was a link between lichen species identity, reproductive strategy, and photobiont selectivity. We show high photobiont specificity and selectivity within the forest landscape: only five closely related tRNA(Leu) (UAA) intron genotypes were found from 232 Nephroma thalli. Two Nostoc genotypes were shared by N. bellum and N. resupinaturn, while N. parile associated with two different genotypes. One genotype was only found from some specimens of N. resupinaturn. On a single tree trunk all thalli of an individual lichen species usually housed the same photobiont strain, and the lichen species that mainly dispersed with fungal diaspores (N. bellum and N. resupinaturn) usually shared identical photobionts. Both patterns were attributed to a founder effect presumably caused by relatively low colonization rates between trees. The photobiont spectrum of the symbiotically dispersing N. parile indicates that it maintained its own cyanobacterial symbionts. Our study shows that mycobionts of the diverse Nephroma guild do not exchange their cyanobacterial photobionts at random, and that reproductive strategy is reflected in species photobiont choice.