蓝果杜鹃与马缨花杜鹃的自然杂交研究 
马永鹏 
学位类型博士
导师张长芹 
2010-11
学位授予单位中国科学院研究生院
学位专业植物学
摘要自然杂交在物种的生殖隔离和形成过程中,都起着重要的作用。但是自然杂交的另一个意义是当一个广布物种和稀有物种杂交时,可能会导致稀有物种的濒危,但这方面的研究并不是很多。我们的研究对象是一个分布区极其狭窄的杜鹃花属植物蓝果杜鹃(Rhododendron cyanocarpum Franch. exW.W. Sm)和一个广泛分布的杜鹃花属植物马缨花杜鹃(R. delavayi Franch.)。通过地理分布调查、形态的比较分析、繁殖生物学及其分子生物学方法揭示了蓝果杜鹃和马缨花杜鹃自然杂交的过程、杂交区的构成及意义并初步分析了亲本和杂交个体后代适应性方面的问题,其结果具体如下:1. 地理分布调查与形态性状比较: 我们对已知的6个蓝果杜鹃分布点进行调查,只在大理苍山花甸坝找到一个杂交区。通过对选取的形态性状的观察和测量,初步确定了所发现的杂交个体是由蓝果杜鹃和马缨花杜鹃自然杂交所形成。在所选取的22个形态性状中,中间性状占45%,超亲性状占14%。结果表明,中间性状在杂交个体中较为普遍。另外,超亲性状的生态适应意义尚不清楚。2. 繁殖生物学研究: 我们通过对蓝果杜鹃繁殖生物学的研究,得到以下结论:(1) 花色多态性的实验结果表明,无论从红色花植株在各居群所占得比例还是访花昆虫的访花频率来看,粉色花都是有优势的。所以,蓝果杜鹃的粉色花较白色花可能有更强的适应性。 (2) 蓝果杜鹃的有效传粉昆虫是熊蜂,其传粉方式是以熊蜂为媒介的同株异花授粉。(3) 蓝果杜鹃的果实主要由5心皮或6心皮构成,并且各心皮果实所占的比例是与海拔高度(r=0.807, p<0.01)和果实在花序轴的位置(r=0.62, p<0.01)具有显著的相关性。同时,不同心皮数目的果实,在种子重量、数目和萌发率方面都有着显著的差异。对于马缨花杜鹃,实验表明,蜜腺和斑点的作用,共同保证了其繁殖的成功。因为去掉退化蜜腺花冠的座果率显著高于去掉含有花蜜的蜜腺花冠的座果率。我们以蓝果杜鹃、马缨花杜鹃及其杂交个体的花分别作为父本和母本的相互授粉实验表明,每个处理都不同程度的产生了果实,证明马缨花杜鹃、蓝果杜鹃和杂交个体之间的种间生殖隔离较弱,易于杂交。对同域分布的马缨花杜鹃和蓝果杜鹃的访花昆虫观察表明,熊蜂是它们之间共有的传粉昆虫。所以,花期的重叠、种间较弱的生殖隔离和共有的传粉昆虫,为蓝果杜鹃和马缨花杜鹃自然杂交的发生,提供了繁殖生物学层方面的证据。3. 自然杂交的分子生物学证据: 我们通过比较分析2个核基因片段 (ITS和Waxy) 和3个叶绿体基因片段(TrnC-F, trnH-psbA和TrnL-rpl32) 的变异位点,证明了这些具有中间性状的杂交个体确实是马缨花杜鹃和蓝果杜鹃自然杂交形成的,而且这一杂交过程是不平衡的双向杂交,其中主要是以马缨花杜鹃为母本 (90%),极少以蓝果杜鹃为母本 (10%)。4. 杂交区的构成分析: 我们通过分子测序和分子标记两种方法,揭示了该杂交区的性质:(1)该杂交区的构成是由亲本、F1代、F2代及回交后代组成;(2)F2代数量均超过了F1代和回交后代;(3)该杂交区的基因流方向是单向的,即从蓝果杜鹃流向马缨花杜鹃。基因流的单向性和杂交区的少量杂交个体这两个事实,表明至少目前这一杂交过程尚未加剧蓝果杜鹃的濒危。但是考虑到该杂交区可能是近期形成的,随着以后生境破坏的加剧,大量杂交个体会不断涌现,进而可能威胁到蓝果杜鹃的生存。5. 杂交个体及其亲本后代的适合度初步研究: 我们对各基因型种子的一些指标进行初步比较发现,杂交个体的后代在任何阶段,并不都是低于双亲的适合度。如胚根长、胚轴长、株高等方面,在实验条件下杂交个体后代的观测指标显著的高于亲本马缨花杜鹃。所以,我们有理由推测,在原始生境发生巨大变化的条件下,杂交个体是有可能与亲本有着相似或更强的适应能力的。
资助项目Natural hybridization has many evolutionary consequences, such as the origin of new ecotypes or species and the maintenance of reproductive barriers. However, few studies have involved in and quantified the potential threat to rare species by natural hybridization. In this study, we focused on the hybridization between a narrow endemic species R. cyanocarpum Franch. ex W.W. Sm and the widespread species R. delavayi Franch.. We revealed this process of natural hybridization, composition and possible significance of the detected single hybrid zone and comparative analysis of fitness among parental species and the hybrids. These significant results were summarized as follows: 1. Field observation and comparative analysis of morphological characters, We investigated 6 sites where R. cyanocarpum distributed, and found the single putative hybrid zone only in one site. 22 morphological characters were selected and measured, according to which the putative parental species were determined. Among the examined morphological characters, intermediate characters accounted for 45%, whereas the transgressive characters accounted for 14%. These results showed that intermediate characters were predominant. In addition, the ecological adaptations of these transgressive characters remain unknown. 2. Reproductive biology and reproductive evidence for natural hybridization, Three main results were achieved via the study of pollination biology of R. cyanocarpum: (1) from the results of floral color experiments, we found that the pink flowers have preponderant adaptation over the white ones. Because either proportions of individuals with pink flowers within and between populations, or visitation rate of pollinators were all significant higher than white types; (2) the effective pollinators of R. cyanocarpum were solely the bumblebees (Bombus festivces and B. richardsi), and the pollination is primarily due to geitonogamy that is mediated by bumblebees; (3) most of fruits were either composed of 5 or 6 carpels. Moreover, the proportions of carpel number per fruit were significantly related to the altitudes ((r=0.807, p<0.01) and the positions of inflorescence (r=0.62, p<0.01). Meanwhile, seed weight, seed number and seed germination rate were significant difference to the fruits with different carpel number; For R. delavayi, the experiment showed that the associated function of nectary and spots promote reproductive success in R. delavayi, because of significantly higher fruit production was examined in half petal deprived with degenerative nectarines than in half petal deprived with normal ones. Reciprocal hand pollination treatments showed that either species, as pollen donor or pollen receiver, could produce fruits indicating weak reproductive barriers between species. It was noted that fruit set varied among treatments. The same pollinators (bumblebees) were shared in both parental species. Therefore, flowering period overlapping, weak reproductive barriers and sharing the same pollinators, all contributed to reproductive evidence for the possible occurrence of natural hybridization between R. cyanocarpum and R. delavayi. 3. Molecular evidence for natural hybridization, On the basis of two nuclear DNA (ITS and Waxy) and three chloroplast DNA (trnC-F, trnH-psbA and trnL-rpl32), hybrids and parental species were clearly identified and individuals with intermediate morphologies are indeed of hybrid origin from natural hybridization between R. cyanocarpum and R. delavayi. Hybridization occurred in both directions, but was asymmetrical, with R. delavayi as the major maternal parent (90%) whereas only one hybrid had identical chloroplast to R. cyanocarpum (10%). 4. The study of hybrid zone, Two molecular methods were employed to successfully disclosed characters of the single hybrid zone: (1) this hybrid zone was composed of parental species, F1s, F2s and backcross derivatives; (2) F2s outnumbered either F1s or backcross derivatives; (3) the direction of gene flow was from R. cyanocarpum to R. delavayi. Based on the one directional gene flow and fewer hybrids formation in the single hybrid zone, no threat to R. cyanocarpum posed by natural hybridization was observed. However, such a threat is likely to arise if more hybrids are produced via serious habitat disturbance. 5. Comparative analysis of fitness among parental species and hybrids, We made a preliminary result that the fitness of hybrids’ offspring is not always lower than their parental offsprings, after comparative analysis of some detected fitness index in experimental condition, such as the lengths of radicle and hypocotyls, and the seedling height. Therefore, it is reasonable to presume that these hybrids can have similar or higher fitness than parental species only if natural habitat is changed substantially in a short period.
语种中文
文献类型学位论文
条目标识符http://ir.kib.ac.cn/handle/151853/16164
专题昆明植物所硕博研究生毕业学位论文
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马永鹏 . 蓝果杜鹃与马缨花杜鹃的自然杂交研究 [D]. 中国科学院研究生院,2010.
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