title: Polyploidy in Indian paintbrush (Castilleja; Orobanchaceae) species shapes but does not prevent gene flow across species boundaries.
abstract: OBJECTIVE
  A difference in chromosome numbers (ploidy variation) between species is usually considered a major barrier to gene flow. Therefore, it is surprising that little is known about whether ploidy variation, both within and among species, influences spatial patterns of interspecific hybridization. The role that polyploidy plays in structuring gene flow patterns between three co-occurring Indian paintbrush (Castilleja) species is investigated. •
  
  
  METHODS
  Reciprocal hand pollinations were performed in populations where the three species co-occur with and without variable plants (previous data tested the ancestral "hybrid" history of these variable plants). I measured fruit set, seed production, seed germination, and the DNA content of parent plants and 26 synthesized F(1) hybrids. Data were combined with pollinator fidelity data to estimate the contribution of individual barriers to reproductive isolation. •
  
  
  RESULTS
  Interspecific gene flow could occur in all directions, but barriers were weaker for conspecific vs. heterospecific crosses. Species were nearly fixed for different ploidy levels, but some deviations occurred, primarily in populations with variable plants. Interspecific gene flow could occur across ploidy levels, but it was more likely when species had the same number of chromosomes or when resulting F(1) hybrids had even numbers of chromosomes. Postzygotic reproductive barriers were generally weaker than pollinator fidelity. •
  
  
  CONCLUSIONS
  Polyploidy likely plays a large role in shaping contemporary and historical patterns of gene flow among these species. This study suggests that differences in chromosome numbers among closely related, compatible species might help structure spatial patterns of hybridization.
authors.affiliation: Department of Biological Sciences, Michigan Technological University, Houghton, Michigan 49931 USA. eherschg@mtu.edu
authors.forename: Erika I
authors.initials: EI
authors.lastname: Hersch-Green
mesh_terms: D027901:Acanthaceae / Q000235:genetics*; D000704:Analysis of Variance; D000818:Animals; D002467:Cell Nucleus / Q000235:genetics; D003120:Colorado; D003433:Crosses, Genetic; D018744:DNA, Plant / Q000235:genetics; D005638:Fruit / Q000254:growth & development; D051456:Gene Flow / Q000235:genetics*; D005843:Geography; D018525:Germination / Q000502:physiology; D006824:Hybridization, Genetic; D007313:Insecta / Q000502:physiology; D016015:Logistic Models; D011123:Polyploidy; D060047:Reproductive Isolation; D012639:Seeds / Q000254:growth & development; D013045:Species Specificity
chemical_list: D018744:DNA, Plant