title: Hybridization is associated with changes in sexual system in the bryophyte genus Atrichum.
abstract: OBJECTIVE
  Over 50% of bryophytes have separate sexes, and numerous transitions have occurred between combined and separate sexes. Polyploidy and hybridization is one proximate mechanism hypothesized to cause evolutionary transitions to hermaphroditism in bryophytes because sex is expressed at the haploid stage and in nonpolyploid dioecious species males have a single V chromosome and females a U. Hermaphroditism can arise if gametophytes of allopolyploids have both U and V chromosomes. We examined the association between polyploidy and hermaphroditism in the bryophyte genus Atrichum, which has species where gametophytes can be haploid, diploid, or triploid, and some species have hermaphroditic individuals.
  
  
  METHODS
  We generated phylogenies of Atrichum from sequences of three plastid regions (rbcL, rps4, and trnL-trnF) and the second intron for the nuclear gene Leafy/Floricaula to further understand the relationships among haploid, diploid, and triploid species, and those with combined or separate sexes.
  
  
  RESULTS
  The existence of multiple sequences of Leafy/Floricaula in diploid and triploid, but not haploid, individuals is consistent with independent allopolyploid origins of the diploid and triploid species. Allopolyploidy was associated with a likely gain in hermaphroditism in triploid Atrichum undulatum and possibly diploid A. altecristatum, but not in the allopolyploid A. crispulum (diploid at the gametophyte level).
  
  
  CONCLUSIONS
  These results highlight a role for hybridization and polyploidy in sexual system evolution, but the presence of diploid (allopolyploid) dioecious species suggest that other factors may influence the maintenance of sexual systems after an evolutionary transition.
authors: Department of Biology, University of New Brunswick, 10 Bailey Dr, Fredericton, Canada E3B5A3.
authors: Danielle S
authors: DS
authors: Perley
authors: Department of Biology, University of New Brunswick, 10 Bailey Dr, Fredericton, Canada E3B5A3 Faculty of Biology, University of Marburg, Karl-von-Frisch-Str. 8, D-35043 Marburg, Germany.
authors: Linley K
authors: LK
authors: Jesson
mesh_terms: D005075:Biological Evolution; D044002:Bryophyta / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D019143:Evolution, Molecular; D006824:Hybridization, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012098:Reproduction; D017422:Sequence Analysis, DNA
chemical_list: D010940:Plant Proteins
keywords: Polytrichaceae; allopolyploidy; bryophytes; hermaphroditism; phylogeny; sexual systems