Evolution of lichen symbioses
Lutzoni et al. studied the evolution of lichen symbioses, using a dataset of nuclear large and small subunit rDNA sequences from 56 Ascomycota
Phylogenetic trees were inferred, and switches between lichenized and free-living lifestyles were mapped onto the phylogeny using maximum likelihood methods
Results suggest that there may have been only a single origin of lichenization in the Ascomycota, but that there have been several reversals
Lutzoni et al’s results contradict those of an ealrier study by Gargas et al., which suggested several independent origins of lichenization in the Ascomycota, and no reversals
The conflict among these studies reflects the difficulty of reconstructing patterns of evolution using phylogenetic trees—incomplete or biased sampling is a source of error, but even with complete and correct trees, it can be difficult to “map” characters onto a phylogeny
Gargas, A., P. T. DePriest, M. Grube, and A. Tehler. 1995. Multiple origins of lichen symbiosis suggested by ssu rDNA phylogeny. Science 268: 1492-1495.
Lutzoni, F., M. Pagel, and V. Reeb. 2001. Major fungal lineages are derived from lichen symbiotic ancestors. Nature 411:937-940.