title: Effects of population size on synchronous display of female and male flowers and reproductive output in two monoecious Sagittaria species.
abstract: BACKGROUND
  Flowering synchrony and floral sex ratio have the potential to influence the mating opportunities and reproductive success through female function. Here, we examine the variances in synchronous display of female and male function, ratio of male to female flowers per day and subsequently reproductive output in small populations of two monoecious plants, Sagittaria trifolia and Sagittaria graminea.
  
  
  RESULTS
  We created plant populations of size 2, 4, 10 and 20 and recorded the daily number of blooming male and female flowers per plant to determine daily floral display, flowering synchrony index and ratio of male to female flowers per day. We also harvested the fruits, counted the seeds and calculated the number of fruits and seeds per flower to measure reproductive success through female function. There is less overlap in flowering time of female and male function in smaller populations than in larger populations. Most importantly, we found that male-biased floral sex ratio and imbalanced display period of female and male function for individual plant can lead to a population-size-dependent ratio of male to female flowers per day. Increasing ratio of male to female flowers per day was generally associated with a greater percentage of fruit production.
  
  
  CONCLUSIONS
  Our results highlight the importance of flowering synchrony of female and male function and population-size-dependent ratio of male to female flowers per day for female reproductive success. This finding improves our understanding of a mechanism that reduces reproductive success in small populations.
authors.affiliation: Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, the Chinese Academy of Sciences, Wuhan, China.
authors.forename: Xiufang
authors.initials: X
authors.lastname: Wang
authors.forename: Wen
authors.initials: W
authors.lastname: Zhou
authors.forename: Jing
authors.initials: J
authors.lastname: Lu
authors.forename: Haibin
authors.initials: H
authors.lastname: Wang
authors.forename: Chan
authors.initials: C
authors.lastname: Xiao
authors.forename: Jing
authors.initials: J
authors.lastname: Xia
authors.forename: Guihua
authors.initials: G
authors.lastname: Liu
mesh_terms: D000465:Algorithms; D000704:Analysis of Variance; D056626:Inflorescence / Q000502:physiology*; D008954:Models, Biological; D056771:Ovule / Q000502:physiology*; D011058:Pollen / Q000502:physiology*; D011156:Population Density; D012098:Reproduction / Q000502:physiology; D034903:Sagittaria / Q000145:classification / Q000254:growth & development / Q000502:physiology*; D013045:Species Specificity; D013997:Time Factors