BREEDING SYSTEMS, POLLEN FLOW, AND CONTINUING EVOLUTION IN AVON GORGE SORBUS (WHITEBEAMS, ROWANS, AND SERVICE TREES)

埃文峡谷是英国最丰富的植物学遗址之一，以其花椒的多样性而在国际上具有重要意义，在19个分类群中记录了3个特有物种和至少3个特有杂种(Rich等人)。2008年)。目前有四种物种被列入世界自然保护联盟濒危物种红色名录：布氏链球菌、威氏链球菌、英国链球菌和隆起链藻(IUCN，2007)。Hiscock和Case Partner Rich最近的研究表明，峡谷中花椒的多样性主要是由有性二倍体S.ucuparia、S.torminaris和(特别是)S.aria与多倍体兼性无融合生殖S.porrigentiformis及其衍生物S.emenens和S.bristoliensis(Robertson等人)杂交产生的。正在准备中)。不同分类群所采用的交配系统的类型对这一持续的进化过程至关重要。这3个有性类群是专性异交体，而杂交多倍体要么是专性无融合生殖(产生无性种子)，要么是兼性无融合生殖(通过无融合生殖和有性生殖相结合的方式繁殖)。在多倍体中，无融合生殖是通过假受精进行的，需要授粉来诱导无性种子发育和产生有性胚乳。然而，重要的是，我们最近的研究表明，由于自交不亲和，稀有的无融合生殖多倍体S.bristoliensis和S.wilmottiana不能利用自体花粉或来自其他同种个体(无性系)的花粉。这就需要它们接受来自其他花椒物种的花粉，特别是花椒属植物的花粉，以便通过假配子产生种子(Robertson等人。正在准备中)。因此，授粉对于花杉类群之间的所有生殖过程以及它们的种群动态和正在进行的进化都是必不可少的。这项研究旨在量化雅芳峡谷花椒属植物之间的花粉运动和花粉限制，并将其与种群动态和正在进行的花椒属新分类群的进化联系起来。然后，这些数据将被用来向我们的合作者、布里斯托尔市议会、自然英格兰和国家信托基金通报最合适的保护战略，以保护稀有的特有花杉物种，并维持在雅芳峡谷内创造花椒多样性的过程。我们的初步发现(Robertson等人研究表明，海南花杉是珍稀的无融合生殖花椒物种生产种子所需的重要花粉来源，这表明在所有花椒保护战略中都需要考虑海南海棠。本研究有两个主要目的：1)研究中国花椒属5个新分类群的交配系统(S)的特征；2)量化雅芳峡谷不同花椒属之间的开花时间、花粉移动和花粉限制，并将其与生殖产量、种群动态和新花椒属正在进行的进化联系起来。特别是，这项工作将确认沙打菌花粉是否确实推动了埃文峡谷花椒的繁殖和正在进行的多样化，并提供了维持这些过程所需的沙打菌数量和密度的估计，并保护了这种稀有特有物种的成功繁殖。这将通过实现以下目标来实现：1.在新描述的尚未测试的花椒属分类群中建立繁殖模式(交配系统)。2.测定花椒属植物开花时间的年变化和季节变化。3.确定花椒传粉者的主要传粉者。4.测定有性花椒属和无融合生殖花椒属的花粉限制。5.利用荧光粉尘和多态微卫星标记估计花椒个体(特别是花椒)的花粉流距离。6.计算花粉邻域并预测影响稀有的假配子无融合生殖体产籽所需的孢子密度。

The Avon Gorge is one of the richest botanical sites in Britain, and is internationally important for its Sorbus diversity, with 3 endemic species and at least 3 endemic hybrids amongst the 19 taxa recorded (Rich et al. 2008). Four species are currently on the IUCN Red List of endangered species: S. bristoliensis, S. wilmottiana, S. anglica and S. eminens (IUCN, 2007). Recent research by Hiscock and CASE partner, Rich, has shown that Sorbus diversity in the gorge is generated primarily by hybridisation between sexual diploids S. aucuparia, S. torminalis, and (especially) S. aria, and the polyploid facultative apomict S. porrigentiformis and its derivatives, S. eminens and S. bristoliensis (Robertson et al. in preparation). The type of mating system employed by the various taxa is pivotal to this continuing evolutionary process. The 3 sexual taxa are obligate outcrossers whereas the hybrid polyploids are either obligate apomicts (producing asexual seed), or facultative apomicts (reproducing by a combination of apomixis and sexual reproduction). In the polyploids, apomixis is via pseudogamy with pollination being required to induce asexual seed development and produce a sexual endosperm. Importantly, however, our recent studies have shown that the rare apomictic polyploids, S. bristoliensis and S. wilmottiana, cannot utilize self-pollen or pollen from other con-specific individuals (clones) because of self-incompatibility. This necessitates that they receive pollen from other Sorbus species, in particular S. aria, in order to produce seeds via pseudogamy (Robertson et al. in preparation). Thus pollination is essential for all reproductive processes among the Sorbus taxa and consequently for their population dynamics and ongoing evolution. This research will aim to quantify pollen movement and pollen limitation among Sorbus taxa in the Avon Gorge and relate this to population dynamics and ongoing evolution of new Sorbus taxa. These data will then be used to inform our collaborators, Bristol City Council, Natural England, and The National Trust, on the most appropriate conservation strategies to preserve rare endemic Sorbus species and to maintain the process responsible for creating Sorbus diversity within the Avon Gorge. Our preliminary findings (Robertson et al. in preparation) indicate that S. aria is an essential source of pollen needed for seed production by the rare apomictic Sorbus species suggesting that S. aria will need to be considered in all Sorbus conservation strategies. The research proposed here has two main aims: 1) to characterize the mating system(s) of the 5 new Sorbus taxa and 2) to quantify flowering time, pollen movement and pollen limitation among the different Sorbus taxa in the Avon Gorge and relate this to reproductive output, population dynamics, and ongoing evolution of new Sorbus taxa. In particular, this work will confirm whether S.aria pollen is indeed driving reproduction and ongoing diversification of Sorbus in the Avon Gorge, and provide estimates of the number and density of S. aria needed to maintain these processes and guaratee successful reproduction of the rare endemic species. This will be accomplished through delivery of the following objectives: 1. Establish modes of reproduction (mating system) in newly described Sorbus taxa not already tested. 2. Determine annual and seasonal variation in flowering time for all Sorbus taxa. 3. Determine the primary pollinators of Sorbus pollinators. 4. Measure pollen limitation among sexual and apomictic Sorbus taxa. 5. Estimate distances of pollen flow from individual Sorbus trees (particularly S. aria) using fluorescent dust and polymorphic microsatellite markers. 6. Calculate pollen neighbourhoods and predict densities of S. aria required to effect seed production in rare pseudogamous apomicts.