title: Combining FISH and model-based predictions to understand chromosome evolution in Typhonium (Araceae).
abstract: OBJECTIVE
  Since the advent of molecular phylogenetics, numerous attempts have been made to infer the evolutionary trajectories of chromosome numbers on DNA phylogenies. Ideally, such inferences should be evaluated against cytogenetic data. Towards this goal, we carried out phylogenetic modelling of chromosome number change and fluorescence in situ hybridization (FISH) in a medium sized genus of Araceae to elucidate if data from chromosomal markers would support maximum likelihood-inferred changes in chromosome numbers among close relatives. Typhonium, the focal genus, includes species with 2n = 65 and 2n = 8, the lowest known count in the family.
  
  
  METHODS
  A phylogeny from nuclear and plastid sequences (96 taxa, 4252 nucleotides) and counts for all included species (15 of them first reported here) were used to model chromosome number evolution, assuming discrete events, such as polyploidization and descending or ascending dysploidy, occurring at different rates. FISH with three probes (5S rDNA, 45S rDNA and Arabidopsis-like telomeres) was performed on ten species with 2n = 8 to 2n = 24.
  
  
  RESULTS
  The best-fitting models assume numerous past chromosome number reductions. Of the species analysed with FISH, the two with the lowest chromosome numbers contained interstitial telomeric signals (Its), which together with the phylogeny and modelling indicates decreasing dysploidy as an explanation for the low numbers. A model-inferred polyploidization in another species is matched by an increase in rDNA sites.
  
  
  CONCLUSIONS
  The combination of a densely sampled phylogeny, ancestral state modelling and FISH revealed that the species with n = 4 is highly derived, with the FISH data pointing to a Robertsonian fusion-like chromosome rearrangement in the ancestor of this species.
authors: Department of Biology, University of Munich (LMU), D-80638 Munich, Germany.
authors: Aretuza
authors: A
authors: Sousa
authors: Natalie
authors: N
authors: Cusimano
authors: Susanne S
authors: SS
authors: Renner
mesh_terms: D000782:Aneuploidy; D029064:Araceae / Q000166:cytology / Q000235:genetics*; D001483:Base Sequence; D032461:Chromosomes, Plant / Q000235:genetics*; D020732:Cytogenetic Analysis; D018744:DNA, Plant / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D019143:Evolution, Molecular; D005819:Genetic Markers / Q000235:genetics; D017404:In Situ Hybridization, Fluorescence; D016013:Likelihood Functions; D010802:Phylogeny; D018087:Plastids / Q000235:genetics; D013045:Species Specificity; D016615:Telomere
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal; D005819:Genetic Markers
keywords: 45S rDNA; 5S rDNA; Ancestral trait reconstruction; Araceae; Bayesian inference; FISH; Typhonium; aneuploid chromosome numbers; chromosome evolution; maximum likelihood inference; telomeres