Glaettli Mélanie, Barrett Spencer C H
Department of Ecology and Evolutionary Biology, 25 Willcocks Street, University of Toronto, Toronto, Canada, M5S 3B2.
Present address: Department of Biology, Institute of Plant Sciences, Altenbergrain 21, University of Bern, 3013 Bern, Switzerland.
New Phytol. 2008;179(4):1193-1201. doi: 10.1111/j.1469-8137.2008.02532.x.
In animal-pollinated plants with unisexual flowers, sexual dimorphism in floral traits may be the consequence of pollinator-mediated selection. Experimental investigations of the effects of variation in flower size and floral display on pollinator visitation can provide insights into the evolution of floral dimorphism in dioecious plants. Here, we investigated pollinator responses to experimental arrays of dioecious Sagittaria latifolia in which we manipulated floral display and flower size. We also examined whether there were changes in pollinator visitation with increasing dimorphism in flower size. In S. latifolia, males have larger flowers and smaller floral displays than females. Visitation by pollinators, mainly flies and bees, was more frequent for male than for female inflorescences and increased with increasing flower size, regardless of sex. The number of insect visits per flower decreased with increasing floral display in males but remained constant in females. Greater sexual dimorphism in flower size increased visits to male inflorescences but had no influence on the number of visits to female inflorescences. These results suggest that larger flower sizes would be advantageous to both females and males, and no evidence was found that females suffer from increased flower-size dimorphism. Small daily floral displays may benefit males by allowing extended flowering periods and greater opportunities for effective pollen dispersal.
在具有单性花的动物传粉植物中，花部性状的性别二态性可能是传粉者介导的选择的结果。对花大小和花展示的变化对传粉者访花影响的实验研究，可以为雌雄异株植物花部二态性的进化提供见解。在这里，我们研究了传粉者对雌雄异株宽叶慈姑实验阵列的反应，在该阵列中我们操纵了花展示和花大小。我们还研究了随着花大小二态性的增加，传粉者访花是否有变化。在宽叶慈姑中，雄花比雌花大，但花展示比雌花小。传粉者（主要是苍蝇和蜜蜂）对雄花序的访花比雌花序更频繁，并且无论性别，都随着花大小的增加而增加。雄花每朵花的昆虫访花次数随着花展示的增加而减少，但雌花保持不变。花大小的更大性别二态性增加了对雄花序的访花，但对雌花序的访花次数没有影响。这些结果表明，更大的花大小对雌性和雄性都有利，并且没有发现雌性因花大小二态性增加而受到影响的证据。较小的每日花展示可能通过允许延长花期和增加有效花粉传播的机会而使雄性受益。
