Division of Plant Ecology and Systematics, Biology Department, University of Leuven, Belgium.
Ann Bot. 2013 Apr;111(4):651-61. doi: 10.1093/aob/mct031. Epub 2013 Feb 13.
The establishment of plant populations in novel environments may generate pronounced shifts in floral traits and plant mating systems, particularly when pollinators are scarce. In this study, floral morphology and mating system functioning are compared between recently established and older populations of the annual plant Blackstonia perfoliata that occur in different pollinator environments.
Hand-pollination and emasculation experiments were conducted to assess the extent of pollinator-mediated pollen deposition and pollen limitation, and the contribution of autonomous selfing to total seed production. Detailed measurements of key floral traits were performed to compare the flower morphology and mating system functioning between plants from both pollination environments.
Pollinator-mediated pollen deposition was about twice as low in the recently colonized and pollinator-poor environment compared with the old and pollinator-rich sites, but total seed set was little affected by any type of pollen limitation. The contribution of autonomous selfing to total seed production was higher in the pollinator-poor sites than in the pollinator-rich sites (index of reproductive assurance = 0·56 and 0·17, respectively), and seed production was only poorly affected by selfing, whereas in the pollinator-rich populations selfing reduced total reproductive output by about 40 % compared with outcross pollination. Plants originating from pollinator-poor environments produced smaller flowers that showed significantly lower levels of dichogamy (i.e. protogyny) and herkogamy. These reductions resulted in a 2-fold higher capacity for autonomous selfing under pollinator-free conditions (index of autonomous selfing = 0·81 and 0·41 in plants originating from the pollinator-poor and pollinator-rich environment, respectively).
The results illustrate that plant populations colonizing novel environments can differ markedly in floral morphology and mating system functioning. Due to a temporal shift in the male phase, the breeding system of B. perfoliata shifted from delayed selfing under pollinator-rich conditions towards competing selfing in recently established populations, providing greater reproductive assurance when pollinators and/or reproductive partners are limited.
植物在新环境中建立种群可能会导致花部特征和植物交配系统发生显著变化,尤其是当传粉者稀缺时。在这项研究中,我们比较了在不同传粉者环境中存在的一年生植物黑种草(Blackstonia perfoliata)的新建种群和老种群之间的花部形态和交配系统功能。
进行了人工授粉和去雄实验,以评估传粉者介导的花粉沉积和花粉限制的程度,以及自主自交对总种子产量的贡献。对关键花部特征进行了详细测量,以比较来自两种传粉环境的植物的花形态和交配系统功能。
与古老且传粉者丰富的地点相比,在最近殖民化且传粉者稀少的环境中,传粉者介导的花粉沉积量约低两倍,但总种子产量几乎不受任何花粉限制类型的影响。自主自交对总种子产量的贡献在传粉者稀少的地点高于传粉者丰富的地点(生殖保证指数分别为 0.56 和 0.17),并且自交对种子产量的影响很小,而在传粉者丰富的种群中,自交导致总生殖产量比异交授粉减少约 40%。源自传粉者稀少环境的植物产生的花朵较小,表现出明显较低水平的雌雄异位(即先雌后雄)和雌雄同体(即同花)。这些减少导致在无传粉者条件下自主自交的能力提高了 2 倍(源自传粉者稀少和传粉者丰富环境的植物的自主自交指数分别为 0.81 和 0.41)。
结果表明,在新环境中建立种群的植物在花部形态和交配系统功能方面可能存在显著差异。由于雄性阶段的时间推移,黑种草的繁殖系统从传粉者丰富条件下的延迟自交转变为最近建立的种群中的竞争自交,当传粉者和/或繁殖伴侣受到限制时,提供了更大的生殖保证。