title: Size-dependent gender modification in Lilium apertum (Liliaceae): does this species exhibit gender diphasy?
abstract: OBJECTIVE
  Variation in the relative female and male reproductive success of flowering plants is widespread, despite the fundamental hermaphroditic condition of the majority of species. In many hermaphroditic populations, environmental conditions and their influence on development and size can influence the gender expression of individuals through the formation of hermaphroditic and unisexual flowers. This study investigates the hypothesis that the bulbous, animal-pollinated, perennial Lilium apertum (Liliaceae) exhibits a form of size-dependent gender modification known as gender diphasy, in which the sexual expression of individuals depends on their size, with plants often changing sex between seasons.
  
  
  METHODS
  Variation in floral traits was examined in relation to their size using marked individuals in natural populations, and also under glasshouse conditions. Measurements were taken of the height, flower number, floral sex expression, flower size, flower biomass and pollen production of individuals over consecutive years between 2009 and 2012 in seven populations in south-west China.
  
  
  RESULTS
  Flowers of L. apertum are either perfect (hermaphroditic) or staminate (male) and, in any given season, plants exhibit one of three sex phenotypes: only hermaphrodite flowers, a mixture of hermaphroditic and male flowers, or only male flowers. Transitions between each of these sex phenotypes were observed over consecutive years and were commonly size-dependent, particularly transitions from small plants bearing only male flowers to those that were taller with hermaphroditic flowers. Hermaphroditic flowers were significantly larger, heavier and produced more pollen than male flowers.
  
  
  CONCLUSIONS
  The results for L. apertum are consistent with the 'size advantage hypothesis' developed for animal species with sex change. The theory predicts that when individuals are small they should exhibit the sex for which the costs of reproduction are less, and this usually involves the male phase. L. apertum provides an example of gender diphasy, a rare sexual system in flowering plants.
authors: Key Laboratory for Plant Biodiversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming 650204, Yunnan, China Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun Town 666303, Yunnan, China.
authors: Zhi-Qiang
authors: ZQ
authors: Zhang
authors: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun Town 666303, Yunnan, China.
authors: Xing-Fu
authors: XF
authors: Zhu
authors: Key Laboratory for Plant Biodiversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming 650204, Yunnan, China.
authors: Hang
authors: H
authors: Sun
authors: Key Laboratory for Plant Biodiversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming 650204, Yunnan, China Institute of Tibetan Plateau Research at Kunming, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming 650201, Yunnan, China.
authors: Yong-Ping
authors: YP
authors: Yang
authors: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, M5S 3B2, Canada spencer.barrett@utoronto.ca.
authors: Spencer C H
authors: SC
authors: Barrett
mesh_terms: D002681:China; D035264:Flowers / Q000254:growth & development / Q000502:physiology*; D057850:Hermaphroditic Organisms / Q000254:growth & development / Q000502:physiology; D027762:Lilium / Q000254:growth & development / Q000502:physiology*; D010641:Phenotype; D012098:Reproduction; D012621:Seasons; D019849:Sex Determination Processes
keywords: Lilium apertum; gender diphasy; plant mating systems; plant sexual systems; sex allocation; sex change; size-dependent gender modification