【作者】 李肖夏；

【导师】 郭友好；

【作者基本信息】 武汉大学 ， 植物学， 2013， 博士

【摘要】 中国作为淫羊藿属植物(Epimedium)的起源与分布中心,拥有该属近80%的物种。较少的种间差异性和许多的种间变异使得该属植物的分类学和系统学研究比较困难。很有必要通过更好的方法分析淫羊藿属植物的系统与进化关系。该属植物的一些花部特征表现出明显的种间差异,为研究该属植物的花部适应进化提供了理想的材料。我们针对几个重要的典型的花部特征结合传粉系统以及生殖成功等进行研究,通过几个近缘物种的种间的对比研究来揭示花部特征的进化适应意义。为了探讨花部特征和传粉系统是否在物种之间有差异性,我们对7种淫羊藿属植物进行花部特征测量以及传粉观察。结果表明7个物种具有相似的花部形状,但在某些花部特征上表现出差异性。该属植物多被熊蜂和蜜蜂类传粉。除了E. sutchuenense之外,其它物种都有熊蜂为主要的传粉者。物种之间的传粉者类群的差异主要在是否有蜜蜂作为访花者。有必要结合花部特征和一些其它的因素来探讨昆虫类群在种t间表现出差异性的原因。此外,我们发现花粉数目和胚珠数目表现出种间的正相关关系。人工授粉实验以及花粉管竞争实验表明所有研究的物种均表现为高度的自交不亲和,而且自交花粉管生长存在障碍。花粉呈现理论(PPT)认为,与那些被稀少的但能够有效移出并传递花粉的传粉者传粉的物种相比,被频繁和浪费的传粉者传粉的植物物种,其花粉释放应该更加吝啬和平缓。为了验证这一理论,在具有不同的花药开裂方式和其它花部特征差异的三个近缘种中,我们研究并比较了物种的花粉呈现时序和传粉系统。研究结果表明不同的花药开裂方式和其它花部特征的差异使物种表现出不同的花部包装机制。对于E. sutchuenense和E. franchetii来说,具有特殊花药壁上卷运动的开裂方式与E. mikinorii不运动的开裂方式相比,可以增加花粉的移出。传粉研究表明蜜蜂具有低的传粉效率,与熊蜂相比更浪费花粉。与花粉呈现理论一致,E. sutchuenense渐次的而且比较缓慢的呈现花粉,这种呈现方式可以适应访花较频繁且为浪费型传粉者的蜜蜂。与E. sutchuenense(?)目比,E. franchetii的花粉呈现速度相对较快,以适应具有较高访花效率但数量稀少的熊蜂传粉环境。然而在E. mikinorii中似乎存在一个悖论,以熊蜂和蜜蜂为传粉者且具有较高访花频率的E. mikinorii表现出最快的花粉呈现速度。这种呈现方式可以降低蜜蜂对花粉的浪费,也可能是对较短的花寿命的一种适应(不足一天),以增加柱头落置花粉的机会。本研究揭示了花粉呈现策略在淫羊藿属植物中的进化生态的适应性。同时也表明在任何一个物种中,花粉呈现时序是花药开裂方式、花部特征和传粉系统之间相互作用的结果。避免性别干扰(self-interference)被认为是花部形态进化的重要选择力量。雌雄异位(herkogamy)和雌雄异熟(dichogamy)被认为均可以有效的避免性别干扰,但是这两个花部特征对避免干扰可能具有不同的作用。在野外观察中发现,淫羊藿属植物常具有不同程度的雌雄异位和雌雄异熟,并具有自交不亲和性。我选取四个淫羊藿属物种来研究雌雄异位和雌雄异熟对避免性别下扰的作用,旨在验证这个假说：在该属植物中,雌雄异熟和雌雄异位可能分离而单独存在,并且其中一个花部特征可能会被优先选择。我们发现E.franchetii和E. mikinorii具有明显的雌雄异位和轻微的雌雄异熟(或者雌雄同熟),而E. sutchuenense(?)E.leptorrhizum则具有轻微的雌雄异位程度和不完全雄性先熟。野外调查表明所有物种的两性功能分离不会对花粉移出和花粉落置产生影响,因此所有物种均不存在物理性的性别干扰。具有轻微雌雄异位的物种,其自交的程度(自动自交和协助自交)要显著高于具有较大雌雄异位的物种。人工授粉实验表明,在每个物种中自花授粉会显著降低异花授粉的雌性生殖力,而且证明在野外条件下E.sutchuenense和E. leptorrhizum存在性别干扰并降低结实率,但是在E. franchetii和E. mikinorii中则不存在这样的情况。综合以上结果表明,在这四个物种中比较发达的雌雄异位能比雌雄异熟能更有效的降低性别干扰。我们验证了这个假说,在淫羊藿属植物中,雌雄异位应该代替雌雄异熟被优先选择,并进化成可以有效避免性别干扰的一种机制,而且可能不需要与雌雄异熟共同进化以避免性别干扰。通过对两个同域分布的淫羊藿属植物的野外调查和传粉观察发现,E.sutchuenense所有居群的传粉者为蜜蜂,E.franchetii的一个居群为熊蜂传粉,另一个居群为蜜蜂传粉。我们选取3个E. sutchuenense居群和具有不同传粉系统的两个E. franchetii居群作为研究对象,综合比较传粉频率,不同传粉者的访花效率,以及雌雄异位与访花效率的相关性,并结合生殖成功来探讨蜜蜂对两个淫羊藿属物种的传粉生态影响。研究结果表明两个淫羊藿属植物的居群之间的花部特征均无显著性差异。结合考虑居群的生境情况,我们推测很有可能是人为养蜂对两个物种的传粉系统造成影响。蜜蜂在E. sutchuenense(?)中是低效率的传粉者,而在E. franchetii中则具有和熊蜂几乎一样的传粉效率。蜜蜂在物种间的传粉效率差异性归因于雌雄异位程度的差异性。由于E. franchetii具有较大程度的雌雄异位,蜜蜂可以降低单次访问的花粉移出并增加柱头上的花粉落置。尽管蜜蜂在E. franchetii中具有较高的访花频率和传粉效率,但可能由蜜蜂的访花行为引起的同株授粉降低了生殖成功。E. sutchuenense具有较低的生殖成功并表现出花粉限制,推测可能是由于蜜蜂对花粉的浪费造成花粉数量限制,以及轻微的雌雄异位可能增加自花花粉的落置,从而降低雌性适合度。蜜蜂的访花行为和一些花部特征相结合,比如雌雄异位和雌雄异熟,对于探讨蜜蜂对植物的传粉系统和生殖成功具有重要的生态学意义。更多还原

【Abstract】 China is the modern geographical distribution center of Epimedium and hosts approximately80%of species in this genus. Few interspecific differences and many intraspecies varation make it particularly difficult in taxonomy and phylogeny. It is necessary to use better methods in analyses the system and evolution of Epimedium. Some floral traits obviously varied among species, which provided an ideal study system to explore the adaptation of floral traits in Epimedium. We aimed at several important and typical floral traits combined with pollination systems and reproductive success, and used a comparative study in several related species to investigate the evolutionary adaptation of floral traits.To explore the difference of floral traits and pollinator types among species, we conducted measurement of floral traits and pollination observation in seven Epimedium species. Results showed that these species had similar flower morphology, and also some difference in floral traits among species. The species were pollinated by bumblebees and honyebes. Except for E. sutchuenense, bumblebees were the main effective pollinators in other six species. The interspecies difference in pollinator types mainly depended on whether honeybees were as pollinators. So it is necessary to comprehensively explore the cause of pollinator difference among plant species. We observed that there was a positive relationship between pollen number and ovule number among species. The experiments of artificial pollination and pollen tube competition showed that all species were high self-incompatibility, and there was an obvious barrier in the growth of self-pollen tubes in each species.Pollen presentation theory (PPT) predicts that plant species typically pollinated by frequent and wasteful pollinators ought to be much more parsimonious and only gradually release pollen compared to plant species pollinated by infrequent pollinators that are efficient at delivering the pollen they remove. To test PPT, we compare the pollen presentation schedules and pollination systems in three related Epimedium species, having different pollinators. Results showed that differences in anther dehiscence and flowering traits resulted in different pollen packaging schedules. For E. sutchuenense and E. franchetii, a special’roll-up’movement of the anther wall during anther dehiscence increased pollen removal compared to the dehiscence pattern in E. mikinorii, which lacked the’roll-up’movement. Investigations revealed that honeybees had a higher pollen removal rate and lower stigmatic pollen load compared to bumblebees. In accordance with PPT, E. sulchuenense presents pollen sequentially and slowly for the frequent and wasteful honeybees. In comparison to E. sutchuenense, E. franchelii had a faster presentation rate and was adapted to the efficient and infrequent bumblebees. However, E. mikinorii was pollinated by both bumblebees and honeybees at high frequency and had the fastest pollen presentation. This pattern could reduce pollen wastage by honeybees and might be an adaptation to its short flower longevity (less than1day), to increase the chances of pollen deposition on stigmas. The study revealed the evolutionary and ecological adaptation of pollen presentation schedules in the three Epimedium species. And also indicates that pollen presentation schedules can be a consequence of interactions among anther dehiscence, flowering traits and pollination environments for a given species.Self-interference is one of the most important selective forces in shaping floral evolution. Herkogamy and dichogamy can both achieve reductions in the extent of self-interference, but they may have different roles in minimizing self-interference in a single species. Varying degrees of herkogamy and dichogamy can be commonly observed in Epimedium with self-incompatibility in the field. Four Epimedium species endemic to China were selected to explore the roles of herkogamy and dichogamy in avoiding self-interference. We sought to test the hypothesis that in the genus, herkogamy and dichogamy might be separated and become selected preferentially. We observed that two species (E.franchetii and E. mikinorii) expressed strong herkogamy and weak protogyny (adichogamy) while another two species (E. sutchuenense and E. leptorrhizum) expressed slight herkogamy and partial protandry. Field investigations indicated that there was no physical self-interference between male function and female function regarding pollen removal and pollen deposition in all species. Self-pollination (autonomous or facilitated) was greater in species with slight herkogamy than those with strong herkogamy. Artificial pollination treatments revealed that self-pollination could reduce out-crossed female fertility in all species, and we found evidence that self-interference reduced seed set in E. sutchuenense and E. leptorrhizum in the field, but not in E. franchetii and E. mikinorii. These results indicate that well-developed herkogamy is more effective compared to dichogamy in avoiding self-interference in the four species. In genus Epimedium, herkogamy instead of dichogamy should be selected preferentially and evolved as an effective mechanism of avoiding self-interference and might not need to evolve linked with dichogamy. Our field surveys and pollination observation of two sympatry Epimedium species showed that all populations of E. sutchuenense were exclusively pollinated by honeybee, and one population of E. franchetii was pollinated by bumblebee, but honeybees were the main pollinators in another population of E. franchetii which was near many introduced honey hives. We selected three pupolations of E. sutchuenense and the two distinct populations of E. franchetii as our objects. We comprehensively compared the floral characteristics, pollination frequency, pollination efficiency and reproductive success to explore the effect of honeybee on the pollination ecology in the two Epimedium species. Our results showed that there was no difference of floral characteristics amony species and populations. Considering the habitat of pupolations, we infered that human beekeeping very likely had affected pollination system of the two Epimedium species. Honeybees were low-efficiency pollinators of E. sutchuenense, but in E. franchetii, honeybees had nearly equal efficiency with bumblebees. The different pollination efficiency of honeybees between the two Epimedium species was due to the distinct extent of herkogamy. A larger extent of herkogamy in E. franchetii could reduce pollen removal and increase pollen deposition on stigmas during one visit by honeybees. Although honeybees with high pollination frequency and efficiency could be as effective pollinators compared to bumblebees, honeybees reduced reproductive success probably owing to geitonogamy. Moreover, E. sutchuenense had lower reproductive success and expressed pollen limitation in all populations. We inferred that abundant pollen wasted by honeybees caused pollen quantity limitation, moreover, slight herkogamy would increase self-pollen deposition thus reduced female fitness. Pollination behavior of honeybees combined with some floral traits (e.g. herkogamy or/and dichogamy) is important to explore the ecological impact of honeybees on pollination system and reproductive success in plant species.更多还原