“Anther rubbing, a new mechanism that actively promotes selfing in plants”
Mohamed Abdelaziz, Mohammed Bakkali, José M. Gómez, Enrica Olivieri, and Francisco Perfectti (Jan 2019)
Anther rubbing, a new movement discovered in plants, promotes prior selfing
Most plants have developed mechanisms to prevent self-fertilization and its detrimental effects of inbreeding depression. Traits promoting selfing in plants have been approached mainly from the perspective of a loss of function, or even only considered as a by-product of non-adaptive evolutionary processes. However, the shift from cross-fertilization to selfing has been identified as one of the most frequent evolutionary transitions. Therefore, adaptive mechanisms actively promoting selfing should be usual in the plant kingdom, but, remarkably, they have not been frequently found.
In this study, Abdelaziz et al. describe anther rubbing, a mechanism based in autonomous, repeated, and coordinated movements of the stamens over the stigma during flower opening that promotes self-fertilization in a Brassicaceae species. The researchers use time-lapse video and micro-photography to document this novel reproductive mechanism. They also demonstrate experimentally that anther rubbing is sufficient to achieve maximal reproductive output in this plant. This mechanism is different from the known cases of delayed self-pollination because it assures self-pollination even before the flowers will be exposed to the visit of pollinators. This work demonstrates that elaborated mechanisms, including continuous and repeated movements, can evolve in plants to promote self-pollination. Since the evolution of mating systems in plants is a very active research field, this work will establish a new perspective in the study of the evolution of plant diversity and their mating system strategies.
Self-fertilization has recurrently evolved in plants, involving different strategies and traits, often involving loss of attractive functions, collectively known as the selfing syndrome. However, few traits have been described that actively promote self-fertilization. Here we describe a novel mechanism promoting self-fertilization in the Brassicaceae species Erysimum incanum. This mechanism, which we called anther rubbing, consists of autonomous, repeated, and coordinated movements of the stamens over the stigma during flower opening. We have documented anther rubbing by time-lapse videos and experimentally show that it causes self-pollen deposition on stigmas and is sufficient to achieve maximal reproductive output in E. incanum. We predict that these movements should occur in species with limited inbreeding depression, and indeed we find that inbreeding depression in seed production is negligible in this species. While many studies have documented complex floral traits that promote outcrossing, the occurrence of anther rubbing demonstrates that plants can evolve elaborate and under-appreciated adaptations to promote self-fertilization.