title: Allozyme diversity and morphometrics of Melocactus paucispinus (Cactaceae) and evidence for hybridization with M. concinnus in the Chapada Diamantina, North-eastern Brazil.
abstract: OBJECTIVE
  Melocacatus paucispinus (Cactaceae) is endemic to the state of Bahia, Brazil, and due to its rarity and desirability to collectors it has been considered threatened with extinction. This species is usually sympatric and inter-fertile with M. concinnus, and morphological evidence for hybridization between them is present in some populations. Levels of genetic and morphological variation and sub-structuring in populations of these species were assessed and an attempt was made to verify the occurrence of natural hybridization between them.
  
  
  METHODS
  Genetic variability was surveyed using allozymes (12 loci) and morphological variability using multivariate morphometric analyses (17 vegetative characters) in ten populations of M. paucispinus and three of M. concinnus occurring in the Chapada Diamantina, Bahia.
  
  
  RESULTS
  Genetic variability was low in both species (P = 0.0-33.3, A = 1.0-1.6, H(e) = 0.000-0.123 in M. paucispinus; P = 0.0-25.0, A = 1.0-1.4, H(e) = 0.000-0.104 in M. concinnus). Deficit of heterozygotes within the populations was detected in both species, with high values of F(IS) (0.732 and 0.901 in M. paucispinus and M. concinnus, respectively). Evidence of hybridization was detected by the relative allele frequency in the two diaphorase loci. High levels of genetic (F(ST) = 0.504 in M. paucispinus and 0.349 in M. concinnus) and morphological (A = 0.20 in M. paucispinus and 0.17 in M. concinnus) structuring among populations were found.
  
  
  CONCLUSIONS
  The Melocactus spp. displayed levels of genetic variability lower than the values reported for other cactus species. The evidence indicates the occurrence of introgression in both species at two sites. The high F(ST) values cannot be explained by geographical substructuring, but are consistent with hybridization. Conversely, morphological differentiation in M. paucispinus, but not in M. concinnus, is probably due to isolation by distance.
authors.affiliation: Universidade Estadual de Feira de Santana, Departamento de Ciências Biológicas, Laboratório de Sistemática Molecular de Plantas, Rodovia BR 116, Km 03, Feira de Santana, Bahia, CEP 44.130-460, Brazil. sabrina.lambert@bol.com.br
authors.forename: Sabrina Mota
authors.initials: SM
authors.lastname: Lambert
authors.forename: Eduardo Leite
authors.initials: EL
authors.lastname: Borba
authors.forename: Marlon Câmara
authors.initials: MC
authors.lastname: Machado
authors.forename: Sónia Cristina
authors.initials: SC
authors.lastname: Da Silva Andrade
mesh_terms: D001938:Brazil; D029421:Cactaceae / Q000033:anatomy & histology* / Q000201:enzymology* / Q000235:genetics; D005787:Gene Frequency; D014644:Genetic Variation / Q000235:genetics*; D005828:Genetics, Population; D006824:Hybridization, Genetic / Q000235:genetics*