多倍体植物混合倍性种群的建立机制研究进展

基因组多倍化是物种形成和进化的重要驱动力, 几乎所有植物都经历过至少一次基因组加倍。然而, 由于多倍体植株比二倍体表现出更高的死亡率, 多倍化机制被认为是植物进化的“死胡同”。一些植物物种具有自然混合倍性种群, 即同一物种具有不同倍性, 这为揭示多倍体的进化机制提供了最佳途径。本文从基因组加倍形成多倍体植物开始, 综述了混合倍性种群的形成、建立与维持的研究进展, 探讨了多倍体适应自然环境的种群分化而形成多倍体物种的机制。研究自然混合倍性种群的倍性组成、重复基因的功能分化以及多倍体的生态位分化, 有利于明确混合倍性自然种群的生态适应与维持机理, 以及多倍体植物的进化机制。     

中国部分山茶属植物的染色体数目报告(英文)

本文报道36个种或变种的染色体数目,按张宏达的分类系统涉及到了4个亚属、11个组,其中2个种进行了不同居群的观察。结果表明(详见表1),山茶属植物的染色体基数都是x=15。在自然界,染色体倍性变异从2倍体到8倍体均有,但多数种为2倍体。我们观察的这36个种或变种中,2倍体种有22个,4倍体种3个,6倍体种10个,8倍体种1个。这一系列的多倍性变异,主要表现在种间。此外,同种不同居群间也有不同倍性的变异。例如C. forrestii在不同居群间有2倍体、4倍体和6倍体。而且各个不同倍性的植株表型特征没有明显的变异,估计是同源多倍体或称种内多倍体。     

普陀山主要植物种生态位特征

利用样地调查方法,以物种重要值作为资源状态指标,应用Levins生态位宽度公式和Levins生态位重叠公式对普陀山主要植物种进行了生态位宽度和生态位重叠计算。结果表明:普陀山主要植物群落中,青冈(Cyclobalanopsis glauca)、茶(Camellia sinensis)、薹草(Carex tristachya)的生态位宽度分别在乔、灌、草本层中占有优势地位;而且,各层植物种之间有着不同程度的重叠,表现为草本层>乔木层>灌木层;总体上,各植物种的生态位重叠较小,生态位分化明显,资源利用方式分化较大;分布频度是影响植物种生态位宽度、生态位重叠大小的主要因素之一,分布频度越大,则生态位宽度越大,与其他植物种形成生态位重叠的机率也越大。     

不同干扰条件下荒漠啮齿动物生态位特征

2002和2003年的4、7、10月份在内蒙古阿拉善荒漠区设开垦区、轮牧区、过牧区和禁牧区4个不同类型的干扰区,每个干扰区布设4个固定样方,对荒漠啮齿动物的空间生态位及其季节特征进行了研究。结果表明:五趾跳鼠和子午沙鼠的空间生态位宽度指数最高,分别为0.925和0.908;短尾仓鼠、小毛足鼠和草原黄鼠的次之,分别为0.789、0.782和0.711;五趾心颅跳鼠的最低,为0.003。草原黄鼠与小毛足鼠等6个种对的空间生态位重叠指数最高,均大于0.9,接近于1,生态位几乎完全重叠。长爪沙鼠与五趾心颅跳鼠、三趾心颅跳鼠的空间生态位重叠指数均为0,不存在资源利用竞争。在荒漠生境中,啮齿动物不仅对不同干扰条件的适应性较强,而且对资源利用存在较大程度的趋同性。在不同干扰条件下荒漠啮齿动物的生态位宽度会随着不同季节的变化出现明显的改变。同样,生态位重叠和生态位分化随着不同生态季节的变化也会发生明显的改变,春、秋季的生态位重叠程度低,分化程度高,秋季较春季略强;夏季的生态位重叠程度高,而分化程度低。     

中华猕猴桃和美味猕猴桃的倍性变异及地理分布研究

根据已有的猕猴桃自然地理分布资料,通过对中华猕猴桃（Actinidia chinensis）和美味猕猴桃（A．deliciosa）野外分布居群的详细调查,利用流式细胞技术对我国西部高原台地向中东部丘陵平原过渡地带6个纯中华猕猴桃、1个纯美味猕猴桃和5个中华／美味猕猴桃同域分布居群共276个个体的倍性进行了检测。结果表明：（1）中华猕猴桃存在二倍体和四倍体,美味猕猴桃存在四倍体、五倍体和六倍体;（2）中华猕猴桃和美昧猕猴桃在经度和纬度的分布上存在显著差异（P〈0．05）,中华猕猴桃在经度上偏东分布而美味猕猴桃偏西,纬度分布上中华猕猴桃偏南而美味猕猴桃偏北;而且不同倍性小种在经、纬度分布上呈现显著差异（P〈0．05）,二倍体、四倍体、六倍体的分布在经度上依次从东到西、纬度上从南到北;（3）中华猕猴桃和美味猕猴桃不同倍性小种的海拔分布存在显著性差异（P〈0．05）,二倍体小种分布海拔最低,四倍体小种次之,六倍体小种海拔分布最高,但通过LSD分析四倍体个体和六倍体个体在海拔分布上不存在显著差异（P〉0．05）。通过对中华／美味猕猴桃这两种具有重要经济价值的果树的倍性变异及地理分布的探讨,提出了猕猴桃倍性小种分布的上述规律并给猕猴桃种质资源收集、评价、创新和可持续利用方面提供了初步的研究基础,尤其是为我国猕猴桃新品种选育提供了基础数据和科学依据。     

中华猕猴桃和美昧猕猴桃的倍性变异及地理分布研究

根据已有的猕猴桃自然地理分布资料,通过对中华猕猴桃（Actinidia chinensis）和美味猕猴桃（A．deliciosa）野外分布居群的详细调查,利用流式细胞技术对我国西部高原台地向中东部丘陵平原过渡地带6个纯中华猕猴桃、1个纯美味猕猴桃和5个中华／美味猕猴桃同域分布居群共276个个体的倍性进行了检测。结果表明：（1）中华猕猴桃存在二倍体和四倍体,美味猕猴桃存在四倍体、五倍体和六倍体;（2）中华猕猴桃和美昧猕猴桃在经度和纬度的分布上存在显著差异（P〈0．05）,中华猕猴桃在经度上偏东分布而美味猕猴桃偏西,纬度分布上中华猕猴桃偏南而美味猕猴桃偏北;而且不同倍性小种在经、纬度分布上呈现显著差异（P〈0．05）,二倍体、四倍体、六倍体的分布在经度上依次从东到西、纬度上从南到北;（3）中华猕猴桃和美味猕猴桃不同倍性小种的海拔分布存在显著性差异（P〈0．05）,二倍体小种分布海拔最低,四倍体小种次之,六倍体小种海拔分布最高,但通过LSD分析四倍体个体和六倍体个体在海拔分布上不存在显著差异（P〉0．05）。通过对中华／美味猕猴桃这两种具有重要经济价值的果树的倍性变异及地理分布的探讨,提出了猕猴桃倍性小种分布的上述规律并给猕猴桃种质资源收集、评价、创新和可持续利用方面提供了初步的研究基础,尤其是为我国猕猴桃新品种选育提供了基础数据和科学依据。     

乌鲁木齐达坂城山区地衣生态位特征的研究

为揭示达坂城山区地衣对生境资源的利用状况及竞争程度,该研究在野外设置30个样方并调查其物种盖度数据,利用生态位宽度、生态位重叠指数及排序分析,探讨达坂城山区地衣的生态位特征及环境影响因子。结果表明:(1)达坂城山区生态位最宽的为丽黄鳞衣(Rusavskia elegans)和内卷野粮衣(Circinaria contorta),对不同环境具有较强的适应性,其他地衣物种生态位宽度较窄,对环境资源利用程度低。(2)物种间生态位重叠值整体偏低,生态位重叠值较高的物种对极少,地衣物种生态位分化程度高,物种间竞争不激烈。(3)生态位较宽的物种与多数物种之间都存在生态位重叠,但重叠值较低; 一些生态位较窄的物种与其他物种之间的生态位重叠值较高; 生态位重叠和生态位宽度之间并无直接的线性关系。(4)地衣物种沿海拔梯度分布具有差异,海拔、光照强度、湿度、风速和人为干扰是本地区地衣群落物种生态位特征差异的主导环境因子。综上所述,达坂城山区地衣物种由于生境资源的竞争占据各自独特的生态位,形成了生态位的分化,群落较为稳定,沿海拔梯度的生境条件差异是物种差异分布的重要原因。该研究可为地衣群落构建研究提供理论依据,并对该地区地衣物种的多样性和生境保护具有重要意义。     

基于MaxEnt模型的贵州省楠木潜在适生区预测

为揭示楠木(Phoebe zhennan)在贵州省潜在分布特征及其对环境因子的响应模式，该研究基于楠木在贵州省的地理分布点，运用最大熵模型(MaxEnt)与地理信息系统(ArcGIS)方法，结合气候、土壤及地形等30个环境因子，预测楠木在贵州省的潜在适生区，并分析了影响楠木生长的主要环境因子。结果表明：(1) MaxEnt模型AUC平均值为0.843,对贵州省楠木地理分布预测结果良好；楠木潜在适生区呈现以贵州省东北为重点区，从北到南、由东向西适生等级依次降低的趋势，高适生区主要在黔东北铜仁市、黔北遵义市中东部。(2)楠木在贵州省的潜在分布面积为80 013.47 km²,占全省总面积的45.4%,其中高适生区面积占全省总面积的17.4%。(3)等温性(Bio3)、最暖季度降水量(Bio18)、最湿月降水量(Bio13)、最干月降水量(Bio14)、最冷月最低温(Bio6)和温度季节性变动系数(Bio4)等是影响楠木在贵州省潜在分布的重要环境因子。该研究结果为贵州省楠木资源保护区划、种苗扩繁、造林推广与开发利用提供了科学依据。     

闽楠(Phoebe bournei, Lauraceae)地理分布及随气候变化的分布格局模拟

掌握气候变化对珍稀濒危物种的分布和适应性变化趋势的影响，是开展保护生物学研究的基础。闽楠（Phoebe bournei）是我国东部亚热带森林的优势树种，也是金丝楠木的主要来源树种。它具有重要的经济、园林与生态价值，目前已被列为国家II级保护植物。预测不同气候背景下该物种的地理分布格局可为这一珍贵树种的资源保护、合理利用与开发提供指导依据，同时也为闽楠的起源与地理分化研究奠定基础。本研究基于闽楠的123个分布点信息与19个气候因子，采用最大熵模型（MaxEnt）与ArcGIS空间分析，构建闽楠于末次冰期（距今22000年）、当前（1950-2000年）以及未来（2050年与2070年）相应地潜在分布区格局，并确定未来受威胁的适生区、面积与影响分布的气候因子。结果表明：闽楠的适生区覆盖浙江、福建、江西、广东、广西、湖南、湖北、贵州及重庆，制约闽楠地理分布的气候因子主要是温度季节性变化标准差（Bio4）、最暖月最高温（Bio5）与最干季降水量（Bio17）；在末次盛冰期闽楠退缩到我国东部的许多山区，诸如武夷山、浙闽丘陵、武陵山、雪峰山、湘黔桂毗邻的山区；随着全球气候变暖，到2050年与2070年闽楠的适生区有着破碎化甚至丧失的风险。     

利用GARP生态位模型预测桔小实蝇（Bactrocera dorsalis）在中国的适生区域

桔小实蝇Bactrocera dorsalis (Hendel)是一种多食性害虫,明确其可能适生的区域对该虫的科学监测及防治意义重大。利用桔小实蝇在我国的已知分布点数据和亚洲地区的14个环境地理变量图层,运用GARP生态位模型结合GIS空间分析模块预测了该虫在亚洲的地理分布。结果表明桔小实蝇可分布在中国、日本、菲律宾、马来西亚、泰国北部、越南、柬埔寨、老挝、缅甸、尼泊尔、巴基斯坦、孟加拉国和斯里兰卡,这与EPPO报道的分布区域一致。将拟合过程中获得的生态位运算法则投影到我国,并考虑模型间的一致性,预测桔小实蝇在我国各省及市县范围的分布：云南大部、四川南部和东部、贵州大部、重庆大部、广西、广东、台湾、香港、澳门、海南、福建、江西、浙江大部、湖南大部、湖北大部、上海、江苏南部、河南局部及安徽部分地区为桔小实蝇的适生区。次适生区沿适生区周围分布,为四川、贵州、重庆、湖北北部、河南南部和江苏南部的一些零星地区。适生区和次适生区大多有较高密度的寄主果树,为桔小实蝇的生存提供了条件。预测结果经独立验证数据的适合性测验表明,选择的最优模型具有显著的统计学意义,显示了很好的预测能力。GARP生态位模型可以解决生态学、生物地理学和环境保护方面的一系列问题,具有广泛的应用前景,为物种已知基础分布点资料的综合分析以及有害生物的适生性分析、监测和防治提供了技术平台。     

Polyploidy associated with altered and broader ecological niches in the Claytonia perfoliata (Portulacaceae) species complex

? Premise of the study: Polyploids are often hypothesized to have distinct and broader niches than their diploid progenitors. Differences in geographic distributions between diploid and polyploids are frequently used to infer niche differentiation and increased breadth, but they are seldom used to test these hypotheses explicitly. ? Methods: Niche overlap and breadth were compared for diploids, tetraploids, and hexaploids of three taxa in the Claytonia perfoliata complex (C. parviflora, C. perfoliata, and C. rubra) with the use of species distribution models. Resampling and randomization approaches were used to test hypotheses of niche differentiation, breadth, and conservatism. ? Key results: Niche differentiation was detected between polyploid and diploid cytotypes assigned to the same taxon (e.g., C. parviflora 2× vs. 4×) but not between hexaploids and tetraploids within a taxon (e.g., C. parviflora 4× vs. 6×). Individual hexaploid cytotypes had broader ecological niches than individual diploid cytotypes. However, as a group the three hexaploid taxa did not exceed the combined niche breadth of the three diploids, suggesting that polyploidy does not result in transgressive niche breadth for this group. Niche overlap was lowest among diploids and was highest among the three hexaploid cytotypes, consistent with introgression associated with polyploidy resulting in greater ecological similarity. Although cytotypes possessed nonidentical niches, after accounting for environmental differences among ranges, cytotypes were more similar than expected, suggesting niche conservatism and similar responses to environmental characteristics. ? Conclusions: These results suggest that polyploids occupy distinct and broader niches relative to diploids but that cytotypes also share fundamentally similar responses to environmental variation across ploidy levels.     

Niche differentiation between diploid and hexaploid <Emphasis Type="Italic">Aster amellus</Emphasis>

The maintenance of separated diploid and polyploid populations within a contact zone is possible due to both prezygotic and postzygotic isolation mechanisms. Niche differentiation between two cytotypes may be an important prezygotic isolating mechanism and can be studied using reciprocal transplant experiments. We investigated niche differentiation between diploid and hexaploid Aster amellus in their contact zone in the Czech Republic. Diploid populations are confined to habitats with low productivity, whereas hexaploid populations occur in habitats with both low and high productivity. Thus, we chose three diploid populations and six hexaploid populations, three in each of the two different habitat types. We analyzed habitat characteristics and carried out reciprocal transplant experiments in the field using both seeds and adult plants. Sites of diploid and hexaploid populations differed significantly in vegetation and soil properties. The mean number of juveniles was higher at sites of home ploidy level than at sites of foreign ploidy level, suggesting niche differentiation between the two cytotypes. On the other hand, transplanted adult plants survived at all sites and juvenile plants were able to establish at some sites of the foreign cytotype. Furthermore, the mean number of juveniles, survival, and flowering percentages were higher at home sites than at foreign sites, indicating local adaptation. We conclude that niche differentiation between the two cytotypes and local adaptation within each cytotype may contribute to the maintenance of diploid and hexaploid populations of A. amellus in their contact zone. Moreover, further factors, such as differences in flowering phenology and exclusion of minority cytotypes, should also be considered.     

Cytotype segregation on regional and microgeographic scales in snow buttercups (Ranunculus adoneus: Ranunculaceae)

Polyploid speciation is an important source of angiosperm diversity. Insights into the origin and establishment of new polyploid species may be gained by studying the distributions of ancestral and derivative cytotypes at multiple spatial scales. Diploid (2n = 16) and tetraploid (2n = 32) snow buttercups (Ranunculus adoneus: Ranunculaceae) occur in the alpine of the central and southern Rocky Mountains. Root-tip squashes and flow cytometry were used to determine the ploidy of 1618 individuals from 35 populations. Samples from 31 of the 35 sites were entirely of one cytotype, either diploid or tetraploid. Diploid and tetraploid snow buttercups have nonoverlapping regional distributions. Where both cytotypes occur on the same site, the two are spatially segregated despite no apparent change in habitat. Triploid snow buttercups were only found at a diploid/tetraploid contact zone, while two hexaploid plants were found in tetraploid populations. Tetraploid establishment once or twice in the history of the species complex could account for the regional distribution of the two cytotypes. Habitat differentiation between cytotypes or reproductive exclusion of minority cytotypes may explain the observed segregation at both microgeographic and regional scales.     

Male meiosis in polyploid silkworms,Bombyx mori L. (Lepidoptera : Bombycidae)

Tetraploid and hexaploid silkworms, Bombyx mori L. (Lepidoptera Bombycidae) were induced by applying a cold shock to diploid and triploid eggs at the first cleavage stage. Male meiosis in the primary spermatocytes of these silkworms having a different ploidy was observed. In the polyploid cells, chromosome bridges, 2 for the tetraploid and 3 for the hexaploid, occurred between the newly formed daughter nuclei at telophase. Observation in the living spermatocytes showed that tetraploid cells needed a longer time than the diploid ones to complete the first meiotic division. The delay in the cell division may be responsible for the high sterility of the tetraploid males.     

Pollen and stomata morphometrics and polyploidy in Eriotheca (Malvaceae‐Bombacoideae)

Approximately 70% of the angiosperm species are polyploid, an important phenomenon in the evolution of those plants. But ploidy estimates have often been hindered because of the small size and large number of chromosomes in many tropical groups. Since polyploidy affects cell size, morphometric analyses of pollen grains and stomata have been used to infer ploidy level. Polyploidy is present in many species of the Cerrado, the Neotropical savanna region in Central Brazil, and has been linked to apomixis in some taxa. Eriotheca gracilipes and Eriotheca pubescens are common tree species in this region, and present cytotypes that form reproductive mosaics. Hexaploid individuals (2n = 6x = 276) are polyembryonic and apomictic, while tetraploid and diploid individuals (2n = 2x = 92, 2n = 4x = 184) are sexual and monoembryonic. We tested whether morphometric analysis can be used to estimate ploidy levels in E. gracilipes and E. pubescens individuals. Pollen material from diploid and hexaploid individuals of E. gracilipes, and tetraploid and hexaploid individuals of E. pubescens, were fixed in 50% FAA, and expanded leaves were dried in silica gel. Pollen grains and stomata of at least five individuals from each population were measured. The results demonstrate that all measures were significantly different among cytotypes. Individuals with higher levels of ploidy (hexaploid) all presented measurements that were higher than those with lower levels (diploid and tetraploid). There was no overlap between ploidy levels in each species at 95% confidence interval. Thus, the size of the pollen grains and stomata are effective parameters for analysis of ploidy levels in E. gracilipes and E. pubescens.     

Ecological differentiation,lack of hybrids involving diploids,and asymmetric gene flow between polyploids in narrow contact zones of Senecio carniolicus (syn. Jacobaea carniolica,Asteraceae)

Areas of immediate contact of different cytotypes offer a unique opportunity to study evolutionary dynamics within heteroploid species and to assess isolation mechanisms governing coexistence of cytotypes of different ploidy. The degree of reproductive isolation of cytotypes, that is, the frequency of heteroploid crosses and subsequent formation of viable and (partly) fertile hybrids, plays a crucial role for the long‐term integrity of lineages in contact zones. Here, we assessed fine‐scale distribution, spatial clustering, and ecological niches as well as patterns of gene flow in parental and hybrid cytotypes in zones of immediate contact of di‐, tetra‐, and hexaploid Senecio carniolicus (Asteraceae) in the Eastern Alps. Cytotypes were spatially separated also at the investigated microscale; the strongest spatial separation was observed for the fully interfertile tetra‐ and hexaploids. The three main cytotypes showed highly significant niche differences, which were, however, weaker than across their entire distribution ranges in the Eastern Alps. Individuals with intermediate ploidy levels were found neither in the diploid/tetraploid nor in the diploid/hexaploid contact zones indicating strong reproductive barriers. In contrast, pentaploid individuals were frequent in the tetraploid/hexaploid contact zone, albeit limited to a narrow strip in the immediate contact zone of their parental cytotypes. AFLP fingerprinting data revealed introgressive gene flow mediated by pentaploid hybrids from tetra‐ to hexaploid individuals, but not vice versa. The ecological niche of pentaploids differed significantly from that of tetraploids but not from hexaploids.     

Association of ploidy and sexual system in Lycium californicum (Solanaceae)

In North American Lycium (Solanaceae), the evolution of gender dimorphism has been proposed as a means of restoring outcrossing after polyploidization causes the loss of self-incompatibility. Previous studies of this process in Lycium focused on comparisons between species that differ in ploidy. We examined intraspecific variation in floral morphology and DNA content in populations of L. californicum to determine correlations between sexual system and cytotype. We also used nuclear ITS and GBSSI sequence data to determine whether diploid and polyploid forms represent the same phylogenetic species, and the phylogeographic relationships among populations and ploidy levels. Within populations, no variation in ploidy was found, although among populations there was a perfect correspondence between sexual system and cytotype. Diploid populations were all hermaphroditic, whereas tetraploid populations were all gender dimorphic. There was no clear geographic pattern to the occurrence of diploid and tetraploid forms. Phylogenetic analysis confirms that L. californicum, regardless of ploidy, forms a monophyletic group within the genus Lycium. Sequences from diploid and polyploid individuals did not form reciprocally monophyletic clades, indicating either multiple gains of polyploidy, ongoing gene flow between cytotypes, or lack of lineage sorting since the evolution of polyploidy. The correspondence between ploidy and sex expression is consistent with the hypothesis that polyploidization triggers the evolution of gender dimorphism in this and other Lycium species.     

Studies in the Hordeum murinum L. aggregate: disc electrophoresis of seed proteins

Seeds of the H. murinum aggregate were collected from much of the range of the group and soluble protein extracts were subject to gel-electrophoresis analysis. Diploid, tetraploid and hexaploid plants were readily differentiated. Analysis using a similarity matrix and dendrogram revealed further groups within the ploidy levels and indicated inter-group relationships. Evidence obtained supported karyological results, suggesting that tetraploid and hexaploid plants are allopolyploids, and that one of their putative parents is a diploid known from Turkey and adventive in Australia. Within the tetraploids there is little correspondence between groups detected by either gel-electrophoresis or karyology, and the species H. leporinum (mostly southern) and H. murinum (mostly northern).     

Sesquiterpene lactone patterns in diploid and polyploid Ambrosia dumosa

Diploid, tetraploid and hexaploid populations of Ambrosia dumosa yielded several different sesquiterpene lactone patterns. The distribution of chemical complements is useful in relating the different levels of this polyploid series.     

Ancestry of American polyploid Hordeum species with the I genome inferred from 5S and 18S-25S rDNA

* BACKGROUND AND AIMS: The genus Hordeum exists at three ploidy levels (2x, 4x and 6x) and presents excellent material for investigating the patterns of polyploid evolution in plants. Here the aim was to clarify the ancestry of American polyploid species with the I genome. * METHODS: Chromosomal locations of 5S and 18S-25S ribosomal RNA genes were determined by fluorescence in situ hybridization (FISH). In both polyploid and diploid species, variation in 18S-25S rDNA repeated sequences was analysed by the RFLP technique. * KEY RESULTS: Six American tetraploid species were divided into two types that differed in the number of rDNA sites and RFLP profiles. Four hexaploid species were similar in number and location of both types of rDNA sites, but the RFLP profiles of 18S-25S rDNA revealed one species, H. arizonicum, with a different ancestry. * CONCLUSIONS: Five American perennial tetraploid species appear to be alloploids having the genomes of an Asian diploid H. roshevitzii and an American diploid species. The North American annual tetraploid H. depressum is probably a segmental alloploid combining the two closely related genomes of American diploid species. A hexaploid species, H. arizonicum, involves a diploid species, H. pusillum, in its ancestry; both species share the annual growth habit and are distributed in North America. Polymorphisms of rDNA sites detected by FISH and RFLP analyses provide useful information to infer the phylogenetic relationships of I-genome Hordeum species because of their highly conserved nature during polyploid evolution.