title: No evidence of sexual niche partitioning in a dioecious moss with rare sexual reproduction.
abstract: OBJECTIVE
  Roughly half of the species of bryophytes have separate sexes (dioecious) and half are hermaphroditic (monoecious). This variation has major consequences for the ecology and evolution of the different species. In some sexually reproducing dioecious bryophytes, sex ratio has been shown to vary with environmental conditions. This study focuses on the dioecious wetland moss Drepanocladus trifarius, which rarely produces sexual branches or sporophytes and lacks apparent secondary sex characteristics, and examines whether genetic sexes exhibit different habitat preferences, i.e. whether sexual niche partitioning occurs.
  
  
  METHODS
  A total of 277 shoots of D. trifarius were randomly sampled at 214 locations and 12 environmental factors were quantified at each site. Sex was assigned to the individual shoots collected in the natural environments, regardless of their reproductive status, using a specifically designed molecular marker associated with female sex.
  
  
  RESULTS
  Male and female shoots did not differ in shoot biomass, the sexes were randomly distributed with respect to each other, and environmental conditions at male and female sampling locations did not differ. Collectively, this demonstrates a lack of sexual niche segregation. Adult genetic sex ratio was female-biased, with 2·8 females for every male individual.
  
  
  CONCLUSIONS
  The results show that although the sexes of D. trifarius did not differ with regard to annual growth, spatial distribution or habitat requirements, the genetic sex ratio was nevertheless significantly female-biased. This supports the notion that factors other than sex-related differences in reproductive costs and sexual dimorphism can also drive the evolution of biased sex ratios in plants.
authors.affiliation: Swedish Museum of Natural History, Department of Botany, Box 50007, SE-104 05 Stockholm, Sweden, irene.bisang@nrm.se.
authors.forename: Irene
authors.initials: I
authors.lastname: Bisang
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden and.
authors.forename: Johan
authors.initials: J
authors.lastname: Ehrlén
authors.affiliation: Department of Agricultural Sciences, University of Helsinki, PO Box 27, FI-00014 Helsinki, Finland.
authors.forename: Helena
authors.initials: H
authors.lastname: Korpelainen
authors.affiliation: Swedish Museum of Natural History, Department of Botany, Box 50007, SE-104 05 Stockholm, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Hedenäs
mesh_terms: D018533:Biomass; D019068:Bryopsida / Q000502:physiology*; D017753:Ecosystem; D012098:Reproduction; D013548:Sweden
keywords: Bryophyte; Drepanocladus trifarius; dioecious moss; sex ratio; sex-correlated molecular marker; sexual niche partitioning; sexual reproduction