title: Cytogenetic and molecular evidence suggest multiple origins and geographical parthenogenesis in Nothoscordum gracile (Alliaceae).
abstract: OBJECTIVE
  Nothoscordum gracile is an apomitic tetraploid widely distributed throughout the Americas and naturalized in many temperate regions of other continents. It has been suggested to form a species complex with sexual and apomictic N. nudicaule and N. macrostemon. Tetraploids of these species also share a structurally heterozygous chromosome complement 2n = 19 (13M + 6A). In this work, the origin of N. gracile and its relationships with its related species was investigated based on cytological and molecular data.
  
  
  METHODS
  Cytogenetic analyses were based on meiotic behaviour, CMA bands, localization of 5S and 45S rDNA sites, and genomic in situ hybridization (GISH). Nuclear ITS and plastidial trnL-trnF sequences were also obtained for most individuals.
  
  
  RESULTS
  Proximal CMA bands were observed in the long arms of all acrocentrics of 2x and 4x N. macrostemon but not in diploid and some tetraploid cytotypes of N. nudicaule. Samples of N. gracile showed a variable number of CMA bands in the long arms of acrocentrics. Analysis of ITS sequences, dot-blot, GISH, and 5S and 45S rDNA sites, revealed no differentiation among the three species. The trnL-trnF cpDNA fragment showed variation with a trend to geographical structuring irrespective of morphospecies and fully congruent with karyotype variation.
  
  
  CONCLUSIONS
  The 2n = 19 karyotype was probably formed by a centric fusion event occurring in N. nudicaule and later transmitted to tetraploid cytotypes of N. macrostemon. Diploids of N. nudicaule and N. macrostemon appeared as consistent recently diverged species, whereas tetraploid apomicts seem to constitute an assemblage of polyploid hybrids originating from multiple independent hybridization events between them, part of which are morphologically recognizable as N. gracile.
authors.affiliation: Laboratório de Citogenética Vegetal, Programa de Pós-Graduação em Biologia Vegetal, Departamento de Botânica, CCB, Universidade Federal de Pernambuco, Rua Prof. Nelson Chaves s/n, Cidade Universitária, Recife, PE, Brazil.
authors.forename: Luiz Gustavo Rodrigues
authors.initials: LG
authors.lastname: Souza
authors.forename: Orfeo
authors.initials: O
authors.lastname: Crosa
authors.forename: Pablo
authors.initials: P
authors.lastname: Speranza
authors.forename: Marcelo
authors.initials: M
authors.lastname: Guerra
mesh_terms: D000490:Allium / Q000235:genetics*; D001483:Base Sequence; D005075:Biological Evolution; D032461:Chromosomes, Plant / Q000235:genetics*; D020732:Cytogenetic Analysis; D018744:DNA, Plant / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D005843:Geography; D006239:Haplotypes; D017404:In Situ Hybridization, Fluorescence; D056626:Inflorescence / Q000235:genetics; D059785:Karyotype; D008540:Meiosis / Q000235:genetics; D018519:Meristem / Q000235:genetics; D008938:Mitosis / Q000235:genetics; D008969:Molecular Sequence Data; D010312:Parthenogenesis / Q000235:genetics*; D011003:Ploidies; D017422:Sequence Analysis, DNA
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal