title: Ancient polymorphism reveals unidirectional breeding system shifts.
abstract: Loss of complex characters is thought to be irreversible (Dollo's law). However, hypotheses of irreversible evolution are remarkably difficult to test, especially when character transitions are frequent. In such cases, inference of ancestral states, in the absence of fossil evidence, is uncertain and represents the single greatest constraint for reconstructing the evolutionary history of characters. Breeding system character transitions are of particular interest because they affect the amount and distribution of genetic variation within species. Transitions from obligate outcrossing to partial or predominant self-fertilization are thought to represent one of the most common trends in flowering plants. We use the unique molecular genetic properties (manifested as deep persistent polymorphisms) of the locus that enforces outcrossing to demonstrate that its loss is irreversible in the plant family Solanaceae. We argue that current phylogenetic methods of reconstruction are potentially inadequate in cases where ancestral state information is inferred by using only the phylogeny and the distribution of character states in extant taxa. This study shows in a statistical framework that a particular character transition is irreversible, consistent with Dollo's law.
authors.affiliation: Section of Ecology, Behavior, and Evolution, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, USA. bigic@ucsd.edu
authors.forename: Boris
authors.initials: B
authors.lastname: Igic
authors.forename: Lynn
authors.initials: L
authors.lastname: Bohs
authors.forename: Joshua R
authors.initials: JR
authors.lastname: Kohn
mesh_terms: D000483:Alleles; D005075:Biological Evolution; D003433:Crosses, Genetic; D019143:Evolution, Molecular; D035264:Flowers; D017343:Genes, Plant; D014644:Genetic Variation; D016013:Likelihood Functions; D008390:Markov Chains; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry*; D011058:Pollen; D011110:Polymorphism, Genetic; D019657:Solanaceae / Q000235:genetics; D013997:Time Factors
chemical_list: D010940:Plant Proteins