LUTZONIĘ, FRANCOIS*, MARK PAGELę, AND VALERIE REEBĘ„. ĘDepartment of Botany, The Field Museum, Chicago, IL 60605 USA. ęSchool of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading RG6 6AJ UK. „Department of Biological Sciences, University of Illinois at Chicago (M/C 066), Chicago, IL 60607 USA. - Contribution of the lichen symbiosis to the diversification of ascomycetes: A new approach to determining confidence levels for ancestral character states.
The acceptance by the mycological and lichenological communities, more
than 12 years ago, that basidiomycetes tightly associated with green
algae or cyanobacteria are lichens, simultaneously established, for
the first time, that lichens (including both asco- and basidiolichens)
are derived from multiple independent origins. Because approximately
one-fifth of all known fungi are lichenized and more than 98% of the
diversity of lichens is within the ascomycetes, one crucial question
remains to be answered: How many independent origins of lichens took
place during the evolution of the ascomycetes? To address this
question we have sequenced a 1 kb and a 1.4 kb fragment at the 5' end
of the small and large subunits of the nuclear ribosomal DNA,
respectively, for 54 species representing 31 orders of ascomycetes.
The combined maximum parsimony analysis revealed two equally most
parsimonious trees. The ancestral character states (lichenized versus
non-lichenized) were reconstructed for every node using maximum
likelihood. The confidence levels for each of the ancestral character
states were estimated by reconstructing the evolution of lichenization
on a large number of trees randomly sampled within the confidence
envelope surrounding the best trees.
Key words: ancestral character state reconstruction, comparative methods, lichens, macroevolution, phylogenetics, symbiosis