中国鼠兔属分子系统及进化研究

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	中国鼠兔属分子系统及进化研究
	于宁
学位类型	博士
导师	杜继曾
	1997
学位授予单位	中国科学院西北高原生物研究所
学位授予地点	中国科学院西北高原生物研究所
学位专业	动物学
关键词	鼠兔属线粒体 Dna 限制性片段长度多态（rflp）细胞色素 B基因序列 Nd4 基因序列分子系统树种系发生
摘要	鼠兔属 Ochotona 隶属于哺乳纲、兔形目（ORDER LAGOMORPHA）、鼠兔科（Family Ochotonidae)，为全北界特有科，现生种类属于一单型属。鼠兔属是系统学研究中比较复杂而又较难解决的兔类动物，因此，不少学者先后对已描记的繁杂的学名进行了修订，已解决了许多物种的分类问题，但在少数近缘种上仍存在分歧。对于鼠兔属种间亲缘关系的研究只有零星报道，而且均基于形态特征。本研究收集到鼠兔属产于中国境内的21个物种的材料。首先对6个物种的组织样品利用 mt DNA 限制性片段长度多态技术（RFLP）进行了亲缘关系探讨。因绝大多数材料为标本馆标本的少量皮张，本研究主要利用在种和属水平上进化速度适中的细胞色素 b 和 ND4 基因区作为遗传标记，利用 PCR 技术进行了大量序列测定。基于两个基因的序列数据，分别用简约法和距离法进行了种系发生分析。结果表明：1．序列数据支持某些从形态特征订正出的物种：黄河鼠兔是一个独立物种，而不是藏鼠兔或达乌尔鼠兔的同物异名；甘肃鼠兔为一有效物种，而不应归入藏鼠兔中。努布拉鼠兔亦为独立物种，而作为藏鼠兔或灰鼠兔的同物异名是不恰当的。2．序列数据为我们进行物种订正提供依据。东北鼠兔的分类地位一直是个争论不休的问题，本次的 ND4 基因序列数据表明，东北鼠兔为独立物种，而不应是高山鼠兔的同物异名。新近命名的贺兰山鼠兔是帕氏鼠兔的同物异名。青海鼠兔可能为一有效物种。morosa 确是甘肃鼠兔的亚种，而不是藏鼠兔的同物异名。3．无论是基于单个基因，还是基于两个基因的数据，用简约法还是距离法构建的分子系统树，分为三大支的格局总是稳定的。草原灌丛群包括达乌尔鼠兔、青海鼠兔、高原鼠兔、努布拉鼠兔、甘肃鼠兔、藏鼠兔、托氏鼠兔，支持这7种鼠兔构成单系群的置信度为 100 ％；北方群包括东北鼠兔、高山鼠兔、帕氏鼠兔，支持率为 93 ％以上。黄河鼠兔的位置不定，依所用基因不同，或在草原灌丛群基部，或在北方群基部。其余各种构成高山群，只是支持率不高，而且，用不同的基因及不同的方法构树，得到的内部各种间的关系不同。用 NJ 法构树，个别物种还位于整个系统树的基部。北方群栖息于海拔较低的岩石环境中，分布于42~0N 的地区，远离青藏高原，可能代表了分化较早而比较原始的一类。它们处在生境比较稳定的环境中，因而，物种分化并不明显。草原灌丛群分布于高原及附近海拔较高的地带，是高原抬升而产生的适应相应环境的种类。有趣的是两个基因均显示，灌丛型与草原型在分支图中交错分布，分别组成相应的姐妹群，姐妹群内序列差异很小。而灌丛栖居者之间及草原枉居者之间的分歧程度则很大。这种结果提示草原环境与灌丛环境的鼠兔分化可能是很晚近的事件。而且，在灌丛环境出现之前，整个群内就已经出现了遗传分化。它们形态上的相似性可能是由于适应相似的生境趋同进化的结果。高山群是适应高原高海拔严酷环境的种类。虽然原始类群中可能已经存在变异，但真正分化时间距今时间并不长，由于抬升造成的环境区域化和隔离，或许在分化时并不是按严格二分支的，反应在系统树上就成为多分支。根据化石和地史资料，分子系统树反映的这种格局与青藏高原的间歇性隆升相吻合。4．根据哺乳动物细胞色素 b 10 % ／每百万年的进化速率来推断鼠兔的分歧年代：高原群与其他类群的分歧时间约为 1.2-1.47 百万年；北方群与草原-灌丛群的分期时间约为 0.8-1.0 百万年；而草原和灌丛群的分歧时间仅有 0.2 百万年。根据中国新生代哺乳动物划分的年代，鼠兔属三群的分歧年代分别对应于早更新世泥河湾期中期（Middle Nihewanian-Nihewan Phase）、泥河湾期晚期（Late Nihewanian-Gongwanglin Phase）和中更新世周口店期晚期（Late Zhoukoudianian）。说明推算的分歧年代与地史和哺乳动物年代基本吻合。从我们的研究可以看出，运用形态特征进行种系发生探讨与用分子数据进行系统学研究并不是决然对立的，它们均是种系发生的一部分，都可为重建生物进化历史提供依据。本研究从分子生物学的角度进一步证实鼠兔属的演化是青藏高原抬升所造成的气候和生境变化直接诱导物种基因的改变，经过自然选择，至新物种的出现。而且，分子数据提供的证据更加精细。因此，分子与形态、生物地理、地史与化石相结合，有助于揭示地质演化历史和生物进化历史。
其他摘要	Pikas form a monotypic genus within the family Ochotonidae, Order Lagomorpha. Besides occupying remote and inaccessible habitats, morphological similarities among species of pikas have presented major obstacles to systematists. Although numerous morphological studies have been conducted during the past century, the taxonomic status of some forms of Ochotona remain problematic. However, the phylogeny of pikas is of considerable interest because of their suitability for the study of evolutionary patterns and processes. Unfortunately, few studies on phylogenetic relationships in the genus have been reported. To date, most systematic treatments of Ochotona have been based on morphological characteristics, however, morphology often exhibits phenotypic plasticity and convergent evolution. Smith et al., (1990) suggested that molecular techniques and cladistic analysis would provide the information needed to clarify the systematic relationships of Ochotona. Molecular method offer potentially powerful means to infer phylogenies because they expose genetic variation directly. Mitochondrial DNA, in particular, is an ideal genetic marker for studying relationships among closely related species due to its simple molecular structure, rapid evolution, maternal inheritance, and absence of recombination. In this study, 21 species of Chinese pikas were collected. A total of 26 specimens representing six species and eight forms (included subspecies) from tissue samples were used for mitochondrial restriction fragment length polymorphism (RFLP) analysis. Because most of the samples are from museum specimens, our study had to concentrate on sequencing. A total of 18 and 21 species for mitochondrial cytochrome b and ND4 gene regions (total or partial) have been sequenced. Phylogenetic trees were constructed using both parsimony and distance method from the sequence of the two genes. The following results were obtained. 1. Sequence data support the results from morphological studies: the form huangensis was an independent species rather than a synonym of O. thibetana or O. daurica. The form cansus was also a valid species. As originally described, O. nubrica was a distinct species. It was inappropriate to be treated as a synonyms of O. thibetana or O. roylei. 2. Sequence data provide evidence for the revision of some problematic cases in the systematics of Ochotona, Whether the form hyperborea is a distinct species or a subspecies of O. alpina is a matter of debate. The result from ND4 sequence data give us a clear picture that it was a valid species. The sequence divergence obtained from this study also indicated that O. helanshanensis, a recently described new species, was actually a subspecies of O. pallasi; O. annectens is an independent species and the form morosa should be recognized as a subspecies of O. cansus, rather than O. thibetana. 3. The topology of the trees were relatively robust whether each or both of the genes, parsimony or distance method were used. Three main clusters were apparent. The first one was comprised of shrub-steppe burrowing species (Shrub-Steppe Group) O. daurica, O. annectens, O. curzoniae, O. nubrica, O. cansus, O. thibetana and O. thomasi in 100% of the replicates. The second cluster (Northern Group) contained: O. hyperborea, O. alpina and O. pallasi 93% of the time. O. huangensis was given an unresolved resolution. It is either at the basal of the first cluster (cytb) or at the second cluster (ND4). The third cluster (Mountain Group) included the rest of the species, however, the bootstrap confidence value are low. The relationships of the species within the third cluster were uncertain based on different gene sequence data or methods. 4. The Northern Group are distributed in north of 42~0 N, far from Qinghai-Xizang Plateau. They are rock and talus-dwelling species and probably represented the primitive species group. Within this group, the speciation event are not very strong because of their stable habitat. The Shrub-Steppe Group distributes in the plateau and higher elevation area. The interesting result is that the shrub-dwelling species and steppe species group are intercrossed within the cluster of the phylogenetic tree. For example, O. curzoniae (steppe dwellers) and O. nubrica (shrub dwellers) form a sister group. The sequence divergence within the sister group were very low although the habitant is quite different, while that between the steppe dwelling group and shrub dwelling group were high. This phenomena suggested that the divergence event between the two groups might have happened not long ago. The morphological similarities between the species probably due to the convergent evolution, apparently because morphology has tracked the environment and resulted in adaptive modification in structure that increase the probability of survival. The species within the Mountain Group, typical plateau adapted species, diverged from each other more recently and had probably undergone a rapid radiation. 5. Magnitude of molecular evolution has been used to estimate the age at which lineage have diverged. If the estimate of divergence determined for mammalian mitochondrial cytochrome b (10%/per Ma) is applied to pikas, the Mountain Group diverged from the other two ca. 1.2-1.47 Ma ago. The ancestors of the North Group and the Shrub-Steppe Group diverged from each other ca. 0.8-1.0 Ma ago. The shrub dwelling species diverged from steppe dwellers ca. 0.2 Ma ago. According to the mammal age of Chinese Cenozoic, the divergence of the three groups is correspond to the Middle Nihewanian-Nihewan Phase (1.2-1.8 Ma), Late Nihewanian-Gongwanglin Phase (0.7-1.2Ma) of the early Pleistocene and Late Zhoukoudianian Phase (0.15-0.7Ma) of the middle Pleistocene. The geological studies indicated that the uplift events of the Qinghai-Xizang Plateau occurred more strongly and frequently from 3.4Ma. Among the extensively uplift of the plateau, one at 1.2Ma was a turning point for climatic changes. This event resulted in the temperature decreasing, quickly drier in climatic and followed by the formation of modern desert. Therefore, the divergence time estimates is substantiated by the historical episodes of geologic and climatic changes as well as the fossil records.
页数	117
语种	中文
文献类型	学位论文
条目标识符	http://210.75.249.4/handle/363003/3362
专题	中国科学院西北高原生物研究所
推荐引用方式 GB/T 7714	于宁. 中国鼠兔属分子系统及进化研究[D]. 中国科学院西北高原生物研究所. 中国科学院西北高原生物研究所,1997.

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