title: Transitions between self-compatibility and self-incompatibility and the evolution of reproductive isolation in the large and diverse tropical genus Dendrobium (Orchidaceae).
abstract: OBJECTIVE
  The evolution of interspecific reproductive barriers is crucial to understanding species evolution. This study examines the contribution of transitions between self-compatibility (SC) and self-incompatibility (SI) and genetic divergence in the evolution of reproductive barriers in Dendrobium, one of the largest orchid genera. Specifically, it investigates the evolution of pre- and postzygotic isolation and the effects of transitions between compatibility states on interspecific reproductive isolation within the genus.
  
  
  METHODS
  The role of SC and SI changes in reproductive compatibility among species was examined using fruit set and seed viability data available in the literature from 86 species and ∼2500 hand pollinations. The evolution of SC and SI in Dendrobium species was investigated within a phylogenetic framework using internal transcribed spacer sequences available in GenBank.
  
  
  RESULTS
  Based on data from crossing experiments, estimations of genetic distance and the results of a literature survey, it was found that changes in SC and SI significantly influenced the compatibility between species in interspecific crosses. The number of fruits produced was significantly higher in crosses in which self-incompatible species acted as pollen donor for self-compatible species, following the SI × SC rule. Maximum likelihood and Bayesian tests did not reject transitions from SI to SC and from SC to SI across the Dendrobium phylogeny. In addition, postzygotic isolation (embryo mortality) was found to evolve gradually with genetic divergence, in agreement with previous results observed for other plant species, including orchids.
  
  
  CONCLUSIONS
  Transitions between SC and SI and the gradual accumulation of genetic incompatibilities affecting postzygotic isolation are important mechanisms preventing gene flow among Dendrobium species, and may constitute important evolutionary processes contributing to the high levels of species diversity in this tropical orchid group.
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade Estadual Paulista, 13506-900, Rio Claro, SP, Brazil, biopinheiro@yahoo.com.br.
authors.forename: Fabio
authors.initials: F
authors.lastname: Pinheiro
authors.affiliation: Università degli Studi di Napoli Federico II, Department of Biology, via Cinthia, I-80126, Naples, Italy and.
authors.forename: Donata
authors.initials: D
authors.lastname: Cafasso
authors.affiliation: Università degli Studi di Napoli Federico II, Department of Biology, via Cinthia, I-80126, Naples, Italy and.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Cozzolino
authors.affiliation: Università degli Studi di Napoli Federico II, Department of Biology, via Cinthia, I-80126, Naples, Italy and Institute for Plant Protection, Consiglio Nazionale delle Ricerche, Via Madonna del Piano, 10, I-50019, Sesto Fiorentino (FI), Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Scopece
mesh_terms: D005075:Biological Evolution; D031667:Dendrobium / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics; D012098:Reproduction; D060047:Reproductive Isolation; D017422:Sequence Analysis, DNA
chemical_list: D010940:Plant Proteins
keywords: Character reconstruction; Dendrobium; Orchidaceae; evolution; post-mating barriers; reproductive isolation; self-compatibility; self-incompatibility; speciation