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题名: 中国濒危植物长蕊木兰的繁育系统和遗传多样性研究
作者: 张雪梅
学位类别: 博士
答辩日期: 2008-05-30
授予单位: 中国科学院昆明植物研究所
授予地点: 昆明植物研究所
导师: 龙春林
关键词: 保护 ; 长蕊木兰 ; AFLP标记 ; 遗传多样性 ; 繁育系统 ; 基因流 ; 居群历史
学位专业: 植物学
中文摘要: 长蕊木兰(Alcimandra cathcartii Dandy,木兰科Magnoliaceae)是国家I 级重点保护的野生濒危植物,在《中国物种红色名录》里也被列为了“EN A 2c”物种。根据IUCN 标准,分布于中国的长蕊木兰在过去十年或三个世代内一直在承受着生存威胁,已经有50%的个体消失。我们的野外调查也发现,长蕊木兰曾经的一些分布地点如今已然成为一片光秃的荒地,一些居群也仅以次生植株为主,株体十分脆弱。作为国家重点保护的长蕊木兰,目前的基本生存状态到底如何?它的遗传背景怎么样?本文拟给予回答。本文重点对长蕊木兰的繁育系统和AFLP遗传多样性进行了研究,并结合生态学、(繁殖)生物学特性、居群染色体特征、开花生物学和传粉生物学特性及历史事件,综合地揭示了长蕊木兰的生存状态,探讨了其成因,并提出了保护居群、扩大居群的途径和建议。具体结论如下: 1 生态学、(繁殖)生物学特性及染色体特征 长蕊木兰喜光,零星分布。聚合果中常有种子败育。富含油脂的假种皮常吸引鸟类和松鼠等动物取食种子或将其带离母株。长蕊木兰新鲜种子发芽潜力很高(>90%),但具有生理休眠特性,自然条件下出苗率非常低。 本文首次研究发现,长蕊木兰不同居群之间的核型存在分异,主要表现在染色体类型的不同和随体的有无上。如金平居群的体细胞中期核型公式为2 n = 2 x = 38 = 2 M + 22 m+ 14 sm,屏边居群为2 n = 2 x = 38 = 22 m + 15 sm (3sat) + 1 st。推测可能与地理分布位置不同有关。 2 开花生物学、传粉生物学特性及繁育系统特征 首次观察和研究了长蕊木兰的开花生物学、传粉生物学特性和繁育系统特征。发现,与木兰科内的一些物种(如Magnolia tamaulipana,日本厚朴M. hypoleuca)的开放式样不同,长蕊木兰的花瓣打开后不再闭合,雌雄蕊同时成熟或雌蕊稍早熟于雄蕊。柱头在花未开放时已具可授性,且维持时间较长(约为3天)。花粉寿命最长约为12小时。 花粉是昆虫访花的主要诱物,花瓣次之。观察到的访花昆虫中,膜翅目蜜蜂科(小地蜂、意大利蜂和暗红腹蜂)是最主要的有效传粉者;甲虫类,尤其是叶甲科(金绿沟胫跳甲)和朽木甲科种类也是重要的有效传粉者;食蚜蝇类的传粉作用相对最小。 长蕊木兰具有混合交配系统,既自交亲和,又能通过昆虫或风进行异花授粉。但自然结实率、蓇葖率和结实率都低于人工自交和异交实验结果。较长时间的柱头可授性和本研究中发现的雌蕊群超出雄蕊群的特征是尽可能多地接受自交或异交花粉的信号,但都由于缺乏花粉载体而使得其对成功授粉的贡献不大。缺乏异交花粉和同株授粉或近亲交配导致的近交衰退可能是长蕊木兰自然结实率低的重要原因。 3 遗传多样性水平及其成因 首次研究分析了长蕊木兰的遗传多样性水平后得出,与具有相似生活史特征的物种相比,长蕊木兰具有很低的居群内遗传变异(He = 0.1220),几乎接近于具最低遗传变异水平的自交种类(He = 0.12),居群间遗传分化(Gst = 0.2469)也高于同生活史特征下的一般水平。总体而言,东南部居群(金平、屏边、文山、广南)具有比其它居群较高的遗传变异。三个栽培居群JZ、XC和BZ的期望杂合度值分别为0.1153,0.0942和0.0993,都没有超过各自源居群JP、BS和BS的相应值。 地理距离与遗传距离之间显著的正相关关系(r = 0.6769,P = 0.9980)、对应于居群地理起源的UPGMA聚类(东南部居群组:JP、PB、WS、GN和西部居群组:JH、DU、JD、BS、YD)和小于1的Nm值(0.7626),说明长蕊木兰各自然居群间的基因交流有限,基因交换主要发生于邻近的居群之间。 地质和历史气候变化及人为干扰导致的生境隔离和片段化、一定程度的等位基因随机丢失、有限的基因流(花粉和/或种子散布)和自交亲和但缺乏异交花粉的繁育系统特征可能是长蕊木兰具有低水平的遗传变异和高水平的遗传分化的主要原因。 尽管长蕊木兰总体的遗传多样性较低,但长蕊木兰仍然具有一个主要的生物多样性中心——云南东南部。东南部居群较高的遗传变异和较多的AFLP特有条带,说明了这些居群受到了长期的隔离,而与近期的建立者效应无关。这里在第四纪冰期时未遭到冰川侵蚀,因而在气候上经历了一个逐渐变化而相对稳定的过程,加之特殊的地理环境,云南东南部成为了长蕊木兰生物多样性的一个天然避难所。 4 生存现状及保护建议 零星分布、生境片段化、长距离的花粉和种子传播受限、自然更新能力有限和遗传变异低、遗传分化高是长蕊木兰现有的特点。长蕊木兰的大多数现存居群都已被列入了保护区范围,然而它们的遗传多样性多数都未能代表物种水平的遗传多样性,包括东南部的部分居群在内。因此,应避免对长蕊木兰自然居群生境的进一步破碎化。此外,稀有等位基因可能具有适应特殊环境条件的优势。因而具有最高的遗传变异和最多的特有条带的东南部居群在保护计划中应该给予特别的关注。在进行迁地保护时,至少需要在3个自然居群中采样,才能保护到能代表长蕊木兰物种水平的遗传变异(≥ 95%)。遗传上分化程度最高的PB、DU或JH等居群具有较为特殊的、地方适应性较强的基因型,在进行迁地保护时可以将其作为优先考虑的源居群。
英文摘要: Alcimandra cathcartii Dandy (Magnoliaceae) was appraised the “First Grade” status of the Chinese wild endangered plants that deserves strict protection. Since 2004, it has been listed in the China Species Red List as a category of “EN A 2c” species. Based on the IUCN criteria, A. cathcartii in China has endured persistent threat during the last three generations and has lost at least 50% of its individuals. According to our field observations, the populations are dominated by secondary and weak individuals (e.g., in the population of Heizhiguo Township, Guangnan County in Yunnan Province). In the worst case, a population in Gongpinghe Township, Jingdong County has been totally destroyed and becomes locally extinct there. To make clear the living status of A. cathcartii and to explore its genetic background, we investigated its breeding system and genetic diversity through AFLP marker. Ecological and biological characteristics, chromosome type of different populations, floral and pollination biology and historical events were also studied and analyzed. Finally, a conclusion was made in terms of living status and the cause based on the synthetical data. Some suggestions on protecting and expanding populations were also provided. The major results were as follows: 1. Ecological, biological characteristics and chromosome traits Alcimandra cathcartii distributes sporadically and often grows in sunny places. The fruits are aggregated often bearing inviable seeds. The seeds with arils rich in oil often had themselves eaten and taken away by birds and squirrels. The fresh seeds show very high variability (>90%), whereas they are physiologically dormant, the seedling productivity was very low under natural conditions. Alcimandra cathcartii was found for the first time that it shows differences in karyotypes among different populations mainly presented by the types of chromosome and the occurrence or non-occurrence of microsatellites. For example, the karyotype of JP population can be formulated as 2 n = 2 x = 38 = 2 M + 22 m+ 14 sm, whereas the PB population is 2 n = 2 x = 38 = 22 m + 15 sm (3sat) + 1 st. This may be related to the varied geographic locations of populations. 2. Floral phenology, pollination biology and breeding system characteristics Our study indicates for the first time that the flowers of Alcimandra cathcartii keep unclosed once opening. The gynoecia and stamens often mature simultaneously, and sometimes the anthers dehisce a little later than the petals opening. The stigma without nectar secretion has three-day acceptability or so which occurs before flower opening. The pollens were found to be the main attractants and rewards to insects, and the petals played a minor role. Three species of Hymenoptera, Andrena parvula, Apis mellifera and Sphecodes pieli were the main effective pollinators. Beetles (Coleoptera), especially the Hemipyxis plagioderoides and Alleculidae sp. were also important pollinators. Syrphidae (Diptera) contributed the least to pollination. Alcimandra cathcartii has a mixed-mating system of simultaneous self- and cross-mating by insects and wind-pollination. The fruit set, follicle set per fruit and seed set per fruit from natural pollination are significantly lower than those from either self- or cross-pollination test. The long-time stigma acceptability and the floral characteristic — the gynoecia exceed stamens found in the present study may help receive more self- or cross-pollens, however, are limited by lack of pollen vectors. The low values from natural pollination may be explained by both geitonogamy and pollen shortage. 3. Genetic diversity and the cause of formation Our results suggest for the first time that levels of within-population genetic diversity in A. cathcartii are conspicuously low when compared with other seed plants with similar life history characteristics. If we focus on the genetic diversity index He, the total mean of within-population AFLP diversity in A. cathcartii (He = 0.1220) is nearly equivalent to that of selfers (He = 0.12) which possess the lowest genetic variation. The level of among-population differentiation (Gst = 0.2469) was also higher than the corresponding value of other species with similar life history characteristics. As a whole, the genetic variability measures showed relatively high genetic diversity in the southeast populations than others. All three cultivated populations of JZ, XC and BZ (He = 0.1153, 0.0942 and 0.0993) did not reach the genetic diversity level of their source populations: JP, BS and BS. The Mantel test revealed a significantly positive correlation between genetic and geographic distances among populations (r = 0.6769, P = 0.9980). The UPGMA dendrogram grouped all natural populations of A. cathcartii in one cluster roughly corresponding to their geographic origin. It revealed two large groups: the southeast populations (JP, PB, WS and GN) and the western populations (JH, DU, JD, BS and YD). The Nm value of 0.7626 is lower than the criterion value (Nm ≈ 1) needed to conquer genetic drift. All these data indicate a relatively restricted gene flow among natural populations and the gene exchange is largely restricted to the nearest neighboring populations. Based on a synthetical analysis, the observed low level of genetic diversity and high level of genetic differentiation of A. cathcartii may be primarily due to historical habitat fragmentation resulted from geologic and subsequent climatic changes or human forest-clearing activities, loss of alleles to certain extent, restricted gene flow (seed/pollen dispersal) and the breeding system with self-compatibility without sufficient cross-pollinating pollen supply. At present, Alcimandra cathcartii is harbored in a main center of biodiversity — the southeast Yunnan Province. The comparatively high levels of genetic diversity exhibited in the southeast populations together with the high numbers of “private” AFLP fragments indicate long-term isolation of these populations in this region, rather than the involvement of recent founder events. During the course of the Himalayan Mountain building, the southeast part of Yunnan Province was isolated from the rest as discussed above; and the climate there experienced a gradual change and was thus relatively steady without glacier erosion in the Quaternary. The complex topography in this region may have helped preserve a natural refugium of biodiversity for A. cathcartii. 4. Conservation status and suggestions Alcimandra cathcartii distributes sporadically with fragmented habitat. The species has limited ability in pollen/seed spreading and seedling renewal under natural conditions. It also exhibits a low genetic diversity and a high genetic differentiation. Although most extant populations have been brought into nature reserves, not all the in situ or ex situ populations contain the representative genetic diversity of the species, even in the southeast populations. Therefore, the extant in situ populations should be fully conserved to prevent further habitat destruction. In addition, rare alleles may be important for adapting to unusual environmental conditions. Thus, the southeast populations with the highest genetic diversity and the highest numbers of “private” fragments deserve special attention in the conservation efforts. As for the ex situ conservation plan, at least three natural populations would be required to sample more than 95% of the genetic variation in A. cathcartii. It may be worthwhile to select the genetically most divergent PB, DU or JH population which possesses more specific, locally adapted genotypes as preferential source populations in ex situ conservation programs.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.kib.ac.cn/handle/151853/378
Appears in Collections:昆明植物所硕博研究生毕业学位论文_学位论文

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中国濒危植物长蕊木兰的繁育系统和遗传多样性研究.张雪梅[d].中国科学院昆明植物研究所,2008.20-25
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