title: Evolutionary history of the Afro-Madagascan Ixora species (Rubiaceae): species diversification and distribution of key morphological traits inferred from dated molecular phylogenetic trees.
abstract: OBJECTIVE
  Previous work on the pantropical genus Ixora has revealed an Afro-Madagascan clade, but as yet no study has focused in detail on the evolutionary history and morphological trends in this group. Here the evolutionary history of Afro-Madagascan Ixora spp. (a clade of approx. 80 taxa) is investigated and the phylogenetic trees compared with several key morphological traits in taxa occurring in Madagascar.
  
  
  METHODS
  Phylogenetic relationships of Afro-Madagascan Ixora are assessed using sequence data from four plastid regions (petD, rps16, rpoB-trnC and trnL-trnF) and nuclear ribosomal external transcribed spacer (ETS) and internal transcribed spacer (ITS) regions. The phylogenetic distribution of key morphological characters is assessed. Bayesian inference (implemented in BEAST) is used to estimate the temporal origin of Ixora based on fossil evidence.
  
  
  RESULTS
  Two separate lineages of Madagascan taxa are recovered, one of which is nested in a group of East African taxa. Divergence in Ixora is estimated to have commenced during the mid Miocene, with extensive cladogenesis occurring in the Afro-Madagascan clade during the Pliocene onwards.
  
  
  CONCLUSIONS
  Both lineages of Madagascan Ixora exhibit morphological innovations that are rare throughout the rest of the genus, including a trend towards pauciflorous inflorescences and a trend towards extreme corolla tube length, suggesting that the same ecological and selective pressures are acting upon taxa from both Madagascan lineages. Novel ecological opportunities resulting from climate-induced habitat fragmentation and corolla tube length diversification are likely to have facilitated species radiation on Madagascar.
authors.affiliation: Laboratory of Plant Systematics, KU Leuven, Kasteelpark Arenberg 31, PO Box 2437, BE-3001 Leuven, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Tosh
authors.forename: S
authors.initials: S
authors.lastname: Dessein
authors.forename: S
authors.initials: S
authors.lastname: Buerki
authors.forename: I
authors.initials: I
authors.lastname: Groeninckx
authors.forename: A
authors.initials: A
authors.lastname: Mouly
authors.forename: B
authors.initials: B
authors.lastname: Bremer
authors.forename: E F
authors.initials: EF
authors.lastname: Smets
authors.forename: P
authors.initials: P
authors.lastname: De Block
mesh_terms: D000349:Africa; D005075:Biological Evolution; D018744:DNA, Plant / Q000737:chemistry*; D008270:Madagascar; D019666:Rubiaceae / Q000235:genetics*
chemical_list: D018744:DNA, Plant
keywords: Afro-Madagascan; ETS; ITS; Ixora; Rubiaceae; biogeography; molecular dating; molecular phylogenetics; petD; rpoB-trnC; rps16; trnL-trnF