Message - 7th IAL Symposium

The 7 th International Association for Lichenology Symposium 2012
SYMBIOTIC DISPERSAL AND LICHEN DIVERSITY – NEW INSIGHTS
FROM CENOZOIC FOSSILS AND EXTANT CYANOLICHENS
Rikkinen J. 1
1 Department of Biosciences, University of Helsinki, Helsinki, Finland
Some Paleozoic fossils may represent lichens, but their assignment to extant lineages is not
possible due to their incomplete preservation, and the morphological homoplasy seen in extant lichen
lineages. In contrast, during the Cenozoic numerous lichens were preserved as inclusions in amber.
Some of these fossils are in excellent condition, and allow detailed comparisons with extant genera and
species. Such fossils can be used for minimum age assessment of modern lichen lineages, but also
offer unique evidence of evolutionary stasis in some morphological attributes, including structures that
facilitate symbiotic dispersal in extant lichens. The first part of this presentation summarizes recent,
previously unpublished findings from lichen fossils preserved in Baltic, Bitterfeld, and Dominican amber.
Cyanobacteria participate in many types of symbioses, either serving as a source of fixed carbon and
nitrogen, as in cyanolichens, or solely as a source of nitrogen, as in plant symbioses. Some strains of
Nostoc are common symbionts in lichens and related genotypes are also found in thalloid bryophytes,
cycads, and in the angiosperm Gunnera. Attempts to determine the strain identity of the cyanobacterial
symbiont have only been made for a small fraction of all cyanolichen species. Tropical cyanolichens,
in particular, have so far received very little attention. The second part of the presentation summarizes
findings from ongoing studies on the genetic diversity of cyanobacterial symbionts in lichens and
bryophytes. The topics touched include tripartite lichens, free-living lichen symbionts, and various
community level diversity patterns in arctic, temperate and tropical environments. One unifying theme
in both lines of research is the role of symbiotic dispersal in generating and maintaining biological
diversity among lichen symbionts. The surprising level of genetic variation in modern lichen-symbiotic
Nostoc may be partly explained by genetic drift in small, vertically transmitted symbiont populations.
The Cenozoic lichen fossils show that such processes have had the opportunity to shape the genetic
structure of lichen symbionts over tens of millions of years.
xxvii