Adaptive Significance of Floral Movement

Abstract

Since Darwin observed the reconfiguration of pollinia in orchards and referred to it as a function to reduce self-pollination, diverse floral movements have been investigated and various hypotheses have been proposed to explain their adaptive significance. However, adaptive significance of floral movement in some species has yet to be fully explained. Increasing evidence suggests that some floral movements, which have previously been considered as a mechanism to avoid self-pollination, may act as a mechanism to reduce intrafloral male-female interference. In this review, we first explore insect-induced floral movement—such as secondary pollen presentation—that enhances the efficiency and accuracy of pollination. Secondly, we outline the active movements of different floral structures of pistil (style), stamen (filament, anther, pollen), and corolla, such as flexistyly, pollen sliding and catapulting, and anther rotation. Thirdly, we introduce movement herkogamy, which makes herkogamy decrease or increase via the movements of floral structures, especially decreased approach herkogamy via style curvature in the Malvaceae with a monadelphous column. Fourthly, we highlight the different adaptive significances in floral movements for understanding their evolution, including reduction in intrafloral male–female interference, promotion of outcrossing and/or avoidance of self-pollination, delayed autonomous selfing, and tolerance to harsh environments. In particular, we explore the possibility of three functions of one floral movement in one species, which differs from the generally recognized and conventional notion of one floral movement in one species with only one or two functional mechanisms. Finally, we provide perspectives on the challenges and opportunities for using demographic and molecular genetic approaches to (i) study the relative importance and evolutionary mechanism of different adaptive significances in one floral movement; and (ii) simultaneously investigate the floral movement and correlative traits of broader species in related or unrelated families to test how they evolved and the evolutionary relationship between their functions.

Keywords:

• insect-touched floral movement
• active floral movement
• delayed autonomous selfing
• promotion of outcrossing
• reduction in intrafloral male-female interference
• multiple adaptive significances

ACKNOWLEDGMENTS

This work was jointly funded by the National Natural Science Foundation of China (Grant no. 30500071 to C.-J. Ruan), and the Fundamental Research Funds for the Central Universities (DC10020102).