© 2006 Society of Systematic Biologists
Evolutionary History of Vegetative Reproduction in Porpidia s.l. (Lichen-Forming Ascomycota)
1 University of Chicago, Committee on Evolutionary Biology Culver Hall, Rm. 402, 1025 E. 57th St., Chicago, IL, 60637, USA
2 Field Museum of Natural History, Botany Department 1400 S. Lake Shore Drive, Chicago, IL, 60605, USA
3 School of Animal and Microbial Sciences University of Reading Whiteknights, Reading, RG6 6AJ, UK
4 Sir Harold Mitchell Building, School of Biology, University of St Andrews St Andrews, Fife, KY16 9TH, UK
Edited by Todd Oakley: Associate Editor
Corresponding address: Institute for Forest Genetics and Forest Tree Breeding, Sieker Landstraße 2, 22927 Großhansdorf, FRG. Phone: ++49 (0) 4102/696–145; Fax: ++49 (0) 4102/696–200; j.buschbom{at}holz.uni-hamburg.de
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Abstract |
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The evolutionary history of gains and losses of vegetative reproductive propagules (soredia) in Porpidia s.l., a group of lichen-forming ascomycetes, was clarified using Bayesian Markov chain Monte Carlo (MCMC) approaches to monophyly tests and a combined MCMC and maximum likelihood approach to ancestral character state reconstructions. The MCMC framework provided confidence estimates for the reconstructions of relationships and ancestral character states, which formed the basis for tests of evolutionary hypotheses. Monophyly tests rejected all hypotheses that predicted any clustering of reproductive modes in extant taxa. In addition, a nearest-neighbor statistic could not reject the hypothesis that the vegetative reproductive mode is randomly distributed throughout the group. These results show that transitions between presence and absence of the vegetative reproductive mode within Porpidia s.l. occurred several times and independently of each other. Likelihood reconstructions of ancestral character states at selected nodes suggest that—contrary to previous thought—the ancestor to Porpidia s.l. already possessed the vegetative reproductive mode. Furthermore, transition rates are reconstructed asymmetrically with the vegetative reproductive mode being gained at a much lower rate than it is lost. A cautious note has to be added, because a simulation study showed that the ancestral character state reconstructions were highly dependent on taxon sampling. However, our central conclusions, particularly the higher rate of change from vegetative reproductive mode present to absent than vice versa within Porpidia s.l., were found to be broadly independent of taxon sampling.
Keywords: Ancestral character state reconstructions; Ascomycota, Bayesian inference; hypothesis testing; likelihood; MCMC; Porpidia; reproductive systems
Received November 14, 2004; Revised March 3, 2005; Accepted January 10, 2006
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