PDF(Pubmed)
Abstract：
Dioecious plants are obligate outcrossers with separate male and female individuals, which can result in decreased seed set with increasing distance between the sexes. Wind pollination is a common correlate of dioecy, yet combined wind and insect pollination (ambophily) could be advantageous in compensating for decreased pollen flow to isolated females. Dioecious, ambophilous gymnosperms Ephedra (Gnetales) secrete pollination drops (PDs) in female cones that capture airborne pollen and attract ants that feed on them. Plant sugary secretions commonly reward ants in exchange for indirect plant defense against herbivores, and more rarely for pollination. We conducted field experiments to investigate whether ants are pollinators and/or plant defenders of South American Ephedra triandra, and whether their contribution to seed set and seed cone protection varies with distance between female and male plants. We quantified pollen flow in the wind and assessed the effectiveness of ants as pollinators by investigating their relative contribution to seed set, and their visitation rate in female plants at increasing distance from the nearest male. Ants accounted for most insect visits to female cones of E. triandra, where they consumed PDs, and pollen load was larger on bigger ants without reduction in pollen viability. While wind pollination was the main contributor to seed set overall, the relative contribution of ants was distance dependent. Ant contribution to seed set was not significant at shorter distances, yet at the farthest distance from the nearest male (23 m), where 20 times less pollen reached females, ants enhanced seed set by 30% compared to plants depending solely on wind pollination. We found no evidence that ants contribute to plant defense by preventing seed cone damage. Our results suggest that, despite their short-range movements, ants can offset pollen limitation in isolated females of wind-pollinated plants with separate sexes. We propose that ants enhance plant reproductive success via targeted delivery of airborne pollen, through frequent contact with ovule tips while consuming PDs. Our study constitutes the first experimental quantification of distance-dependent contribution of ants to pollination and provides a working hypothesis for ambophily in other dioecious plants lacking pollinator reward in male plants.
摘要：
雌雄异株植物是专性的异性恋者，具有独立的雄性和雌性个体，随着性别之间距离的增加，会导致种子结实减少。风授粉是dioecy的常见关联，然而，风和昆虫授粉（同时）结合在一起可能有利于补偿花粉流向孤立雌性的减少。雌雄异株，双亲裸子植物麻黄（Gnetales）在雌性视锥细胞中分泌授粉滴（PDs），捕获空气传播的花粉并吸引以它们为食的蚂蚁。植物含糖分泌物通常奖励蚂蚁，以换取植物对食草动物的间接防御，更罕见的是授粉。我们进行了田间试验，以调查蚂蚁是否是南美麻黄的传粉者和/或植物防御者，以及它们对种子结实和种子锥保护的贡献是否随雌性和雄性植物之间的距离而变化。我们量化了风中的花粉流量，并通过调查蚂蚁对种子结实的相对贡献来评估蚂蚁作为传粉者的有效性，以及它们在雌性植物中的访问率，与最近的雄性距离越来越远。蚂蚁占了大多数昆虫对E.triandra雌性视锥细胞的访问，他们在那里消费PD，并且花粉负荷在较大的蚂蚁上较大，而花粉活力却没有降低。虽然风授粉是整个种子结实的主要贡献者，蚂蚁的相对贡献与距离有关。在较短距离，蚂蚁对种子集的贡献不显著，然而，在离最近的雄性(23米)最远的地方，到达雌性的花粉减少了20倍，与仅依靠风授粉的植物相比，蚂蚁的种子结实率提高了30％。我们没有发现任何证据表明蚂蚁通过防止种子锥破坏而有助于植物防御。我们的研究结果表明,尽管他们的短距离运动，蚂蚁可以抵消具有不同性别的风授粉植物的孤立雌性的花粉限制。我们建议蚂蚁通过有针对性地传递空气传播的花粉来增强植物的繁殖成功，通过在食用PD时频繁接触胚珠尖端。我们的研究构成了蚂蚁对授粉的距离依赖性贡献的第一个实验量化，并为雄性植物中缺乏授粉者奖励的其他雌雄异株植物提供了有效的假设。
