The Impact of Reconstruction Methods, Phylogenetic Uncertainty and Branch Lengths on Inference of Chromosome Number Evolution in American Daisies (Melampodium, Asteraceae).
Chromosome number change (polyploidy and dysploidy) plays an important role in plant diversification and speciation. Investigating chromosome number evolution commonly entails ancestral state reconstruction performed within a phylogenetic framework, which is, however, prone to uncertainty, whose effects on evolutionary inferences are insufficiently understood. Using the chromosomally diverse plant genus Melampodium (Asteraceae) as model group, we assess the impact of reconstruction method (maximum parsimony, maximum likelihood, Bayesian methods), branch length model (phylograms versus chronograms) and phylogenetic uncertainty (topological and branch length uncertainty) on the inference of chromosome number evolution. We also address the suitability of the maximum clade credibility (MCC) tree as single representative topology for chromosome number reconstruction. Each of the listed factors causes considerable incongruence among chromosome number reconstructions. Discrepancies between inferences on the MCC tree from those made by integrating over a set of trees are moderate for ancestral chromosome numbers, but severe for the difference of chromosome gains and losses, a measure of the directionality of dysploidy. Therefore, reliance on single trees, such as the MCC tree, is strongly discouraged and model averaging, taking both phylogenetic and model uncertainty into account, is recommended. For studying chromosome number evolution, dedicated models implemented in the program ChromEvol and ordered maximum parsimony may be most appropriate. Chromosome number evolution in Melampodium follows a pattern of bidirectional dysploidy (starting from x = 11 to x = 9 and x = 14, respectively) with no prevailing direction.
Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria.
Jamie
J
McCann
Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria.
Gerald M
http://orcid.org/0000-0003-2811-3317
GM
Schneeweiss
Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria.|Herbarium, Department of Evolution, Ecology, and Organismal Biology, Ohio State University, 318 W. 12th Ave., 43210 Columbus, Ohio, United States of America.
Tod F
TF
Stuessy
Instituto de Biologia, Departamento de Botánica, Universidad Nacional Autónoma de México, Tercer Circuito s/n Ciudad Universitaria Delegación Coyoacán Apartado Postal 70-233, 04510 México, D.F., México.
Jose L
JL
Villaseñor
Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria.
Hanna
H
Weiss-Schneeweiss
D019659:Asteraceae / Q000145:classification / Q000235:genetics*; D001499:Bayes Theorem; D032461:Chromosomes, Plant; D019143:Evolution, Molecular; D016013:Likelihood Functions; D008957:Models, Genetic; D015233:Models, Statistical; D010802:Phylogeny; D011003:Ploidies