Oecologia

, Volume 111, Issue 4, pp 535–542

Evidence of pollen transfer efficiency as the natural selection factor favoring a large corolla of Campanula punctata pollinated by Bombus diversus

  • Shiro Kobayashi
  • Ken Inoue
  • Masahiro Kato

Abstract

Flowers exhibiting a large corolla encompassing a wide inner space, characteristic of bee-pollinated plant species, are postulated to be maintained by a natural selection mechanism related to their pollinators. To confirm the existence and to elucidate the mechanism of such selection, we investigated the effect of floral traits on male reproductive success (RS) and its components in experimental populations of Campanula punctata and C. microdonta (Campanulaceae) under pollination by Bombus diversus (Apidae). Larger corolla width significantly increased male RS per fruit, though there was no effect on pollen removal, showing, for the first time, that a wide corolla serves a reproductive function of enhancing pollen transfer efficiency (ratio of male RS to pollen removal). Selection by pollen transfer efficiency through an indirect effect of initial pollen number or postpollination success was experimentally ruled out. Several mechanisms are proposed to explain how this selection factor is exerted on C. punctata corollas.

Key wordsBombus diversus Campanula punctata Floral trait Male reproductive success Natural selection 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1997

Authors and Affiliations

  • Shiro Kobayashi
    • 1
  • Ken Inoue
    • 2
  • Masahiro Kato
    • 1
  1. 1.Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan Fax: -(81)3-3818-5367; e-mail: ss47201@hongo.ecc.u-tokyo.ac.jpJP
  2. 2.Biological Institute and Herbarium, Faculty of Science, Shinshu University, Matsumoto 390, JapanJP

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