title: Cytotype coexistence leads to triploid hybrid production in a diploid-tetraploid contact zone of Chamerion angustifolium (Onagraceae).
abstract: OBJECTIVE
  Polyploids are often geographically segregated from their diploid progenitors, but the extent of sympatry and the consequences for reproductive isolation and coexistence are rarely quantified. •
  
  
  METHODS
  In this study, we document the distribution and co-occurrence of diploid and tetraploid Chamerion angustifolium among 57 populations within the diploid-tetraploid contact zone in the Canadian Rocky Mountains. Rates of hybrid mating in mixed-ploidy populations were inferred from the frequency of triploid offspring in open-pollinated seed families. •
  
  
  RESULTS
  Twenty-three of 57 populations sampled contained a single cytotype; 20 (87%) were tetraploid and three (13%) were diploid. Thirty-four populations (60%) contained multiple ploidies. Diploid and tetraploid plants occurred in all mixed-ploidy populations; triploids occurred in 13 populations and averaged 1.4% of plants per population. The proportion of tetraploids in a population was negatively related to elevation (partial regression: F = 27.2, P <0.0001) and latitude (partial regression: F = 17.4, P < 0.0001). Triploids were detected in seed from all eight mixed-ploidy populations sampled ( = 3.7% of seed per population), comprising 7% of that expected with random mating (G = 2589.2, df = 1, P <0.0001, n = 2628), and were more often produced by diploid maternal parents than tetraploid parents. •
  
  
  CONCLUSIONS
  Our results indicate that tetraploids regularly coexist with diploids in the contact zone and that this coexistence is likely promoted by both strong reproductive isolation and asymmetric intercytotype mating between diploid and tetraploid C. angustifolium.
authors: Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors: Holly A
authors: HA
authors: Sabara
authors: Paul
authors: P
authors: Kron
authors: Brian C
authors: BC
authors: Husband
mesh_terms: D014644:Genetic Variation; D006824:Hybridization, Genetic; D029594:Onagraceae / Q000235:genetics*; D011003:Ploidies
keywords: Chamerion angustifolium; Onagraceae; fireweed; hybrid mating; polyploidy; reproductive isolation; spatial segregation; triploid