title: Pollination by deceit, floral sex ratios and seed set in dioecious Rubus chamaemorus L.
abstract: Male and female flowers of the dioecious perennial herb Rubus chamaemorus L. are similar in general appearance. However, female flowers are somewhat smaller, do not produce any pollen, and contain very small amounts of nectar. Syrphids and bumblebees, which are important pollinators of R. chamaemorus, showed a strong preference for male flowers. Male flowers were also less often rejected by flower visitors than were female flowers, and two different groups of syrphid species stayed longer in male than in female flowers. These observations suggest that female flowers of R. chamaemorus attract pollinators by deceit.Hand-pollination experiments indicated that pollen availability limited seed production of R. chamaemorus in female dominated habitats but not in areas with an equal floral sex ratio. We suggest that the relative importance of factors limiting female reproductive success is not constant, but is influenced by the floral sex ratio of the population. This should apply also to other dioecious species that show variable sex ratios on either a local or regional scale.
authors.affiliation: Dept. of Forest Site Research, Swedish University of Agricultural Sciences, S-901 83, Umeå, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Ågren
authors.affiliation: Dept. of Ecological Botany, Umeå University, S-901 87, Umeå, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Elmqvist
authors.affiliation: Lab. of Ecological Chemistry, University of Lund, S-223 62, Lund, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Tunlid
keywords: Dioecy; Pollination; Rubus chamdemorus; Seed set; Sex ratio