XTBG OpenIR  > 西双版纳热带植物园毕业生学位论文
玉凤花属植物的繁殖生态学和生殖隔离机制
Alternative TitleReproductive ecology and reproductive isolation mechanisms of Habenaria species (Ochidaceae)
张文柳
Subtype博士
Thesis Advisor高江云
2017-11
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline植物学
Keyword兰科植物 玉凤花属 无融合生殖 生殖隔离 适应进化。
Abstract兰科植物是被子植物中物种最丰富和最进化的类群之一,具有精巧、多样化的花部结构以及独特的吸引传粉者方式,其多样性被认为是适应于多样化特化传粉者的结果。对同属不同形态的兰科植物进行传粉生物学的研究,对了解花部特征与传粉者的适应性关系,理解传粉者在花部进化中的作用具有重要意义。玉凤花属 Habenaria 是最大的地生兰科植物之一,具有丰富的花部特征、传粉机制和繁育系统,是研究花部特征、传粉和植物繁育系统进化的理想植物类群。本文通过对南方玉凤花以及4种同域分布的玉凤花进行传粉生物学的研究,探讨该属植物的传粉和生殖隔离机制,并基于对该属植物繁殖生态学研究的全面总结和把握,探讨玉凤花属植物的传粉机制与花部特征的关系和适应性进化等问题。主要研究结果如下:
1. 南方玉凤花具有专性无融合生殖方式,其不同种群的自然结实率接近100%。从花部特征来看,南方玉凤花不同于别的玉凤花属植物,它的花距缺失或者仅具有很短的不含花蜜的距,并且不能产生挥发性花气味。从人工授粉和种子非共生萌发来看,南方玉凤花6种处理间的人工授粉实验的结实率、种子的有胚、种子的萌发率和幼苗的生长率之间没有显著性差异,其结果都来自于无融合生殖。在花粉管的萌发实验中,花粉块缺失活性,异交花粉在柱头上不能萌发,说明南方玉凤花缺失了有性生殖的特点,无融合生殖的发生不需要花粉的刺激。从传粉者来看,在对南方玉凤花长达91小时的传粉观测中,没有发现有效的传粉昆虫,并且在对连续两年对不同种群的花粉移出和沉降的调查中,没有发现自然条件下花粉的移出和沉降。胚胎学的实验也进一步证实了南方玉凤花的无融合机制是不定胚生殖。我们推测:南方玉凤花无融合生殖的进化,一方面可能是花部特征的变化,使得传粉昆虫不稳定,为了减少资源的消耗并实现繁殖保障,进化出的一种可以获得高的自然结实率的机制;另一方面也可能是因为交配系统的改变与其它控制花部性状的基因连锁,而导致某些花部性状改变。
2. 长距玉凤花 Habenaria davidii、线瓣玉凤花 Habenaria fordii、裂瓣玉凤花 Habenaria petelotii 和宽药隔玉凤花 Habenaria limprichtii 在云南文山具有重叠的花期和重叠的分布区。我们对这四种玉凤花开展了连续三年的繁殖生态学和生殖隔离机制。研究表明,四种玉凤花属植物都是自交亲和的且需要昆虫实现传粉。不同的隔离因素可以有效的减少不同阶段种间的基因交流,并为四个种种最终的生殖隔离形成和物种独立性的维持做出重要贡献。四种玉凤花的同域分布使得地理隔离的作用较弱。根据花期的重叠程度,可以将具有重叠花期的长距玉凤花与线瓣玉凤花分为一组,而将花期完全重叠的宽药隔玉凤花和裂瓣玉凤花分为另一组。宽药隔玉凤花与裂瓣玉凤花因为具有不同的花部特征和生境喜好,它们具有不同的传粉昆虫,因此有较为彻底的合子前隔离机制,人工杂交授粉可以结实,也证实了两者之间的合子后隔离不完全。而长距玉凤花与线瓣玉凤花共享一种传粉昆虫—条背天蛾 Cechenena lineosa,但花粉落置在条背天蛾身体的不同部位,因此花部特征的精细结构以及传粉行为的差异可以有效的减少两者之间花粉的交流。但其合子前隔离并不完全,合子后隔离在长距玉凤花与线瓣玉凤花的生殖隔离中起了重要作用。我们认为,当合子前隔离较弱的时候,合子后隔离起到绝对作用,反之亦然。
3. 综合已有的关于玉凤花属的传粉生物学的报道,以及本文的观察结果,并结合分子系统学证据,我们发现玉凤花属植物具有典型的鳞翅目昆虫传粉的特点,其距的长度和传粉者喙的长度高度吻合。系统树显示玉凤花属植物的距长没有一个明确的从长到短或者从短到长的进化方向,因此我们推测物种形成的模式是适应性进化,其花部特征的差异可能是为了适应不同种类和喙长的传粉昆虫的结果。玉凤花属中存在由夜间传粉向白天传粉转变的趋势,并且这种转变是由玉凤花属植物花颜色和气味对传粉者的吸引以及花的结构对传粉者选择共同作用的结果。无融合生殖是较为进化的繁育系统,可能是由有性生殖转换而来。系统树显示长距玉凤花和宽药隔玉凤花是姐妹亲缘类群,与裂瓣玉凤花的亲缘关系较近,而与线瓣玉凤花的亲缘关系较远。这说明同域分布的长距玉凤花、宽药隔玉凤花和裂瓣玉凤花很可能是适应了不同的生态位和传粉者而就地分化而成,而线瓣玉凤花则是原本异域分化的类群再次混合而来。南方玉凤花与鹅毛玉凤花亲缘关系很近,就本研究得到的两个物种的序列来说,没有表现出遗传变异,但两者的形态差异较大,需要更多的证据来证实两者之间的关系。
Other Abstract
Orchidaceae is one of the most species-rich and advanced plant families, and is renowned for its floral diversity and enormous diversity of pollination mechanisms. Studying the pollination mechanism of orchids within one genus which has greatly various floral characters could provide insights of the adaption of floral characters to pollinators and the role of pollinators in the evolution of plant species. Habenaria is one of the largest terrestrial orchid genera. Its diversity of floral characters, different animal-pollinated system, and breeding system suggested that this family is ideal to understand the ecology and evolution of flowers. In this study, H. malintana and other four co-existing species with different floral characters were selected for studying the reproductive ecology and reproductive isolation. We also tried to explore the adaptive evolution and evolutionary trend in Habenaria by summarizing the floral characters and the pollination system in the genus. The results were summarized as follows:
1. H. malintana is obligate apomict and approximately 100% fruit set was found in different populations and years. From the floral character study, unlike the flowers of other Habenaria species, the flowers of H. malintana have very short spurs with no nectar or scent. In the hand-pollination, seed viability and in vitro seed germination experiments, the fruit sets, seed viability, seed germination ratio and seedling development did not significantly differ among the six different hand-pollination treatments. It suggests that H. malintana is obligate apomict. In pollen germination experiments, hand-depositied pollen failed to germinate on stigmas, strongly suggesting that H. malintana has physiologically lost sexual reproduction, and the seed set did not need to be triggered by pollen grain deposition on stigmas. The flowers of H. malintana failed to attract any pollinators, as we did not observe any floral visitors during 91 h observation period, and no pollinia removal or deposition occurred in both 2013 and 2014 at two study sites. We suggest that this strategy may have evolved to provide reproductive assurance and reduce the cost of flowers in response to unreliable pollinator service, and the flowers traits changes may result from the breeding system shift.
2. In this study, the reproductive ecology and reproductive isolation of four sympatric Habenaria species was investigated in three continuous years during floral periods. Four species were dependent on insects for pollination and completely self-compatible. A number of factors have been identified to limit gene flow among the four species and achieved full reproductive isolation. Ecogeographic isolation was a weak barrier for gene flow among four species. Four species can be divided as two co-flowering species pairs, in which H. fordii and H. davidii had a completely overlapped flowering period, and H. limprichtii completely overlapped with H. petelotii. Complete reproductive isolation between H. limprichtii and H. petelotii was achieved by pre-zygotic isolation including ecogeographic and floral isolation; however, pre-zygotic isolation was weak for H. fordii and H. davidii pair, but post-zygotic isolation strongly acted in the stage of seed production. The results well supported the hypothesis that the species pair with strong pre-zygotic isolation shows incomplete post-zygotic isolation, and vice versa, the species pair with weak pre-zygotic isolation shows strong post-zygotic isolation.
3. Combining previous studies and present results, we reveal that the flowers of many Habenaria species are often characterized by long spurs and achieved pollination by a close association with long-tongued hawkmoths. However, there is not a clear trend to the evolution of the spur length; the radiation may have involved adaptation to different type of pollinators. There is a pollination shift trend from diurnal pollination to nocturnal pollination, and this shift may have result from the effect of floral characters and the floral structure on the pollinator attraction and behavior. In the species of advanced lineage, apomixis in H. malintana is an evolution breeding system, and this strategy may have evolved from an close sexual species. The phylogenetic analysis shows that H. davidii and H. limprichtii are sister groups and has a close relationship with H. petelotii, but all the three species shows distant phylogenetic relationship with H. fordii. That indicate the differentiation of the three species were adapted to the different ecological niche and pollinators, but H. fordii was secondary admixture from different distributed species. H. malintana and H. dentata are close relationship species and they have no genetic variation according to the two sequences in this study. However, the morphological differentiation between them suggested more evidences are needed to identify these two species.
 
Key word: Orchids, Habenaria, apomixis, reproductive isolation, adaptation evolution.

Language中文
Document Type学位论文
Identifierhttp://ir.xtbg.org.cn/handle/353005/10695
Collection西双版纳热带植物园毕业生学位论文
Recommended Citation
GB/T 7714
张文柳. 玉凤花属植物的繁殖生态学和生殖隔离机制[D]. 北京. 中国科学院研究生院,2017.
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