title: Inflorescence architecture affects pollinator behaviour and mating success in Spiranthes sinensis (Orchidaceae).
abstract: • Despite the wide inflorescence diversity among angiosperms, the effects of inflorescence architecture (three-dimensional flower arrangement) on pollinator behaviour and mating success have not been sufficiently studied in natural plant populations. • Here, we investigated how inflorescence architecture affected inter- and intra-plant pollinator movements and consequent mating success in a field population of Spiranthes sinensis var. amoena (S. sinensis). In this species, the flowers are helically arranged around the stem, and the degree of twisting varies greatly among individuals. The large variation in inflorescence architecture in S. sinensis results from variation in a single structural parameter, the helical angle (the angular distance between neighbour-flower directions). • The numbers of visits per inflorescence and successive probes per visit by leaf-cutting bees decreased with helical angle, indicating that individual flowers of tightly twisted inflorescences received less visitations. As expected from pollinator behaviour, pollinia removal and fruit set of individual flowers decreased with helical angle. Meanwhile, geitonogamy decreased in tightly twisted inflorescences. • Our novel findings demonstrate that natural variation in inflorescence architecture significantly affects pollinator behaviour and reproductive success, suggesting that inflorescence architecture can evolve under pollinator-mediated natural selection in plant populations. We also discuss how diverse inflorescence architectures may have been maintained in S. sinensis populations.
authors.affiliation: Graduate school of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan.
authors.forename: Tatsunori
authors.initials: T
authors.lastname: Iwata
authors.affiliation: Toyonaka Municipal The Fourteenth Junior High School, Kitamidorigaoka Toyonaka City, Osaka Prefecture 560-0001, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Nagasaki
authors.affiliation: Graduate School of Science and Engineering, University of Toyama, 3190 Gohuku, Toyama 930-8555, Japan.
authors.forename: Hiroshi S
authors.initials: HS
authors.lastname: Ishii
authors.affiliation: Graduate school of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan.
authors.forename: Atushi
authors.initials: A
authors.lastname: Ushimaru
mesh_terms: D000818:Animals; D001516:Bees / Q000502:physiology*; D005638:Fruit / Q000254:growth & development; D056626:Inflorescence / Q000033:anatomy & histology* / Q000502:physiology*; D007564:Japan; D008954:Models, Biological; D029595:Orchidaceae / Q000033:anatomy & histology* / Q000254:growth & development / Q000502:physiology*; D011058:Pollen / Q000502:physiology; D054817:Pollination / Q000502:physiology*; D012098:Reproduction / Q000502:physiology; D012726:Sexual Behavior, Animal / Q000502:physiology*