title: How much better are females? The occurrence of female advantage, its proximal causes and its variation within and among gynodioecious species.
abstract: BACKGROUND
  Gynodioecy is a reproductive system of interest for evolutionary biologists, as it poses the question of how females can be maintained while competing with hermaphrodites that possess both male and female functions. One necessary condition for the maintenance of this polymorphism is the occurrence of a female advantage, i.e. a better seed production or quality by females compared with hermaphrodites. Theoretically, its magnitude can be low when sterility mutations are cytoplasmic, while a 2-fold advantage is needed in the case of nuclear sterility. Such a difference is often thought to be due to reduced inbreeding depression in obligatory outcrossed females. Finally, variation in sex ratio and female advantage occur among populations of some gynodioecious species, though the prevalence of such variation is unknown.
  
  
  METHODS
  By reviewing and analysing the data published on 48 gynodioecious species, we examined three important issues about female advantage. (1) Are reduced selfing and inbreeding depression likely to be the major cause of female advantage? (2) What is the magnitude of female advantage and does it fit theoretical predictions? (3) Does the occurrence or the magnitude of female advantage vary among populations within species and why?
  
  
  CONCLUSIONS
  It was found that a female advantage occurred in 40 species, with a magnitude comprised between 1 and 2 in the majority of cases. In many species, reduced selfing may not be a necessary cause of this advantage. Finally, female advantage varied among populations in some species, but both positive and negative correlations were found with female frequency. The role of reduced selfing in females for the evolution of gynodioecy, as well as the various processes that affect sex ratios and female advantage in populations are discussed.
authors: Laboratoire GEPV FRE-CNRS 3268, Université des Sciences et Technologies de Lille - Lille 1, Villeneuve d'Ascq Cedex, France. mathilde.dufay@univ-lille1.fr
authors: Mathilde
authors: M
authors: Dufay
authors: Emmanuelle
authors: E
authors: Billard
mesh_terms: D000483:Alleles; D005075:Biological Evolution; D001947:Breeding; D003593:Cytoplasm / Q000235:genetics; D035264:Flowers / Q000235:genetics / Q000502:physiology*; D005819:Genetic Markers; D014644:Genetic Variation; D057850:Hermaphroditic Organisms / Q000502:physiology; D007178:Inbreeding; D019684:Magnoliopsida / Q000145:classification / Q000235:genetics / Q000502:physiology*; D010641:Phenotype; D010802:Phylogeny; D051479:Plant Infertility / Q000235:genetics; D012098:Reproduction; D012639:Seeds / Q000502:physiology*; D012641:Selection, Genetic; D012744:Sex Ratio; D013045:Species Specificity; D013269:Stochastic Processes
chemical_list: D005819:Genetic Markers