Spatial patterns of photobiont diversity in some Nostoc-containing lichens

Patterns of photobiont diversity were examined in some Nostoc-containing li chens using the nucleotide sequence of the cyanobacterial tRNA(Leu)(UAA) in tron. Lichen specimens collected in northwestern USA were analysed and the sequence data were compared with tRNA(Leu)(UAA) intron sequences previously obtained from lichens in northern Europe. Generally, it is the species ide ntity of a lichen rather than the geographical origin of the specimen that determines the identity of the cyanobiont. Identical intron sequences were found in Peltigera membranacea specimens collected in Oregon (USA) and in S weden, and very similar sequences were also found in Nephroma resupinatum t halli collected in Oregon and Finland. Furthermore, in mixed assemblages wh ere two Peltigera species grew in physical contact with each other, the dif ferent lichen species housed different photobiont strains. There is however not a one-to-one relation between mycobiont and photobiont as some intron sequences were found in more than one lichen species, and different intron sequences were found in different samples of some lichen taxa. Peltigera ve nosa exhibited a higher level of photobiont diversity than any other lichen species studied, and several intron sequences could for the first time be obtained from a single thallus. It is not clear whether this is evidence of lower cyanobiont specificity, or reflects an ability to exhibit different degrees of lichenization with different Nostoc strains. In one specimen of P. venosa, which contained bipartite cyanosymbiodemes and tripartite, cepha lodiate thalli, both thallus types contained the same intron sequence.