title: Floral size and shape evolution following the transition to gender dimorphism.
abstract: OBJECTIVE
  Floral morphology is expected to evolve following the transition from cosexuality to gender dimorphism in plants, as selection through male and female function becomes dissociated. Specifically, male-biased dimorphism in flower size can arise through selection for larger flowers through male function, selection for smaller flowers through female function, or both. The evolutionary pathway to floral dimorphism can be most effectively reconstructed in species with intraspecific variation in sexual system. We examined the evolution of flower size and shape inLycium californicum, whose populations are either gender dimorphic with male and female plants, or cosexual with hermaphroditic plants.
  
  
  METHODS
  Floral morphology was characterized in populations spanning the species' complete range. For a subset of the range where cosexual and dimorphic populations are in close proximity, we compared the size and shape of flowers from female and male plants in dimorphic populations to hermaphrodites in cosexual populations, accounting for variation associated with abiotic environmental conditions.
  
  
  RESULTS
  The magnitude of flower size dimorphism varied across dimorphic populations. After controlling for environmental variation across cosexual and dimorphic populations, flowers on males were larger than flowers on females and hermaphrodites, whereas flower size did not differ between females and hermaphrodites. Flower shape differences were associated with mating type, sexual system, and environmental variation.
  
  
  CONCLUSIONS
  While abiotic environmental gradients shape both overall flower size and shape, male-biased flower size dimorphism inL. californicumappears to arise through selection for larger flowers in males but not smaller flowers in females.
authors.affiliation: Department of Biology, Amherst College, Amherst, Massachusetts 01002 USA.|Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138 USA.
authors.forename: Ambika
authors.initials: A
authors.lastname: Kamath
authors.affiliation: Department of Biology, Amherst College, Amherst, Massachusetts 01002 USA.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Levin
authors.affiliation: Department of Biology, Amherst College, Amherst, Massachusetts 01002 USA jsmiller@amherst.edu.
authors.forename: Jill S
authors.initials: JS
authors.lastname: Miller
mesh_terms: D005075:Biological Evolution; D004777:Environment; D035264:Flowers / Q000033:anatomy & histology / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D005843:Geography; D032305:Lycium / Q000033:anatomy & histology / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D051479:Plant Infertility; D012098:Reproduction; D012727:Sex Characteristics; D013045:Species Specificity
keywords: Lycium; Lycium californicum; Solanaceae; dioecy; environmental gradients; floral evolution; gender dimorphism; gynodioecy; male sterility; sexual dimorphism