海草克隆性及其种群遗传效应

海草是适应在海洋环境中生存和繁殖的单子叶植物,由于所处环境常存在潮汐、风暴等的干扰,海草形成了一系列适应特征,克隆性是其中突出的一个.所有的海草都具有水平根状茎,许多海草也具有垂直根状茎,在一些海草中,也观察到无性生殖(无融合生殖).与克隆生长有关的参数(如节间长度、间隔子长度、分枝角度以及延伸速率和分枝率等)对于海草的克隆生长有着决定性影响,但繁育系统对克隆斑块大小也有较大影响.强烈的克隆性影响着海草的遗传变异.总体来看,海草种群内遗传多样性比陆生植物低,也低于另一类海洋高等植物-红树植物,利用DNA标记观察到的多样性高于等位酶标记.在一些海草植物种群中观察到较高的克隆多样性,但也有一些种群由单一基因型或少量基因型组成,其原因主要是由于奠基者效应和克隆生长.通常克隆植物中基因流有限,但是海草的克隆片段可能远距离扩散,从而提高种群间的基因流.就克隆生长对种群空间结构和交配系统的影响进行了综述.     

论克隆植物的遗传多样性

概述了克隆植物的类型与特点 ,对克隆植物的遗传多样性及其遗传结构的一些特点进行了综述 ,并讨论了克隆植物遗传变异的来源。总体而言 ,克隆植物拥有比早期推测大得多的遗传变异 ,虽然克隆种与其近缘有性繁殖种相比 ,遗传多样性较低 ,但广泛的遗传单态性却很罕见。克隆植物种群的遗传结构有所改变 ,广布基因型很少 ,大多数基因型仅分布于某一种群之内 ,种群间基因型多态性存在广泛的变异。不同克隆植物之间遗传多样性相差很大 ,遗传结构也有巨大差异。说明除生殖模式外 ,其他的一些因素 ,如地理分布范围、生境特点 ,散布方式和种群历史等都对克隆植物遗传多样性有重要影响。     

论克隆植物的遗传多样性

概述了克隆植物的类型与特点,对克隆植物的遗传多样性及其遗传结构的一些 特点进行了综述,并讨论了克隆植物遗传变异的来源。总体而言,克隆植物拥有比早期推测大得多的遗传变异,虽然克隆种与其近缘有性繁殖种相比,遗传多样性较低,但广泛的遗传单态性却很罕见。克隆植物种群的遗传结构有所改变,广布基因型很少,大多数基因型仅分布于某一种群之内,种群间基因型多态性存在广泛的变异。不同克隆植物之间遗传多样性相差很大,遗传结构也有巨大差异。说明除生殖模式外,其他的一些因素,如地理分布范围、生境特点,散布方式和种群历史等都对克隆植物遗传多样性有重要影响。     

珍稀濒危植物海南粗榧种群遗传多样性研究

利用RAPD技术对珍稀濒危植物海南粗榧(Cephalotaxus mannii Hook . f.)遗传多样性水平、分布、濒危原因及物种保护等问题进行了探讨.结果表明:1. 海南粗榧在海南岛的5个取样地点表现出低水平的遗传多样性,对环境变化的适应能力不强; 2. 海南粗榧种群内和种群间的遗传多样性所占比例有很大差异,绝大部分变异分布于种群内(DNA多样性为85.1%);种群间仅有较低程度的分化;3. 人为砍伐、植被破坏、台风、被食及遗传漂变是海南粗榧遗传多样性低水平的主要原因,也是物种濒危的主要原因;4. 对于呈零星分布的濒危植物海南粗榧的研究与保护,应充分考虑个体小环境之间的差异,考察影响小种群的随机因素;5. 应采取有力措施,就地保护现有种群,并寻求适当的方法迅速扩展种群,降低基因丧失率;选择遗传多样性较高且破坏相对较小的黎母岭种群作为保护重点;同时应加强对其他种群的保护与管理;6. 海南粗榧种群内、种群间的遗传多样性在不同引物之间有较大差别;多态性位点百分率则是种群间的变化大于引物间的变化.     

珍稀濒危植物海南粗榧种群遗传多样性研究

利用RAPD技术对珍稀濒危植物海南粗榧（Cephalotaxus manniiHook.f.)遗传多样性水平,分布、濒危原因及物种保护等问题进行了探讨。结果表明：1、海南粗榧在海南岛的5个取样地点表现出低水平的遗传多样性,对环境变化物适应能力不强;2、海南粗榧种群内和种群间的遗传多样性所占比例有很大差异,绝大部分变异分布于种群内（DAN多样性为85.1%);种群间仅有较低程度的分化;3、人为砍伐,植被破坏,台风、被食用遗传漂变是海南粗榧遗传多样性低水平的主要原因,也是物种濒危的主要原因;4、对于呈零星分布的濒危植物海南粗榧的研究与保护,应充分考虑个体小环境之间的差异。考虑影响小种群的随机因素;5、应采取有力措施,就地保护现有种群,并寻求适当的方法迅速扩展种群,降低基因丧失率;选择遗传多样性较高且破坏相对较小的黎母岭种群作为保护重点;同时应加强对其他种群的保护与管理;6、海南粗榧种群内,种群音质遗传多样性在不同引物之间有较大差别。多态性位点百分率则是种群间的变化大于引物间的变化。     

森林砍伐对苦槠种群遗传结构的影响

人类活动严重干扰着自然生态系统,其中砍伐是对森林生态系统最常见的干扰之一,它导致森林退化,植物种群变小,甚至灭绝,遗传多样性也随之下降。当被破坏的森林未被转换性利用时,则会逐渐恢复,但由于瓶颈效应,恢复起来的生态系统中植物种群的遗传结构可能会改变。恢复种群遗传组成的改变一方面与干扰的强度、频度和持续时间有关,另一方面,也受植物生活史特点的深刻影响。然而,我国对于砍伐后恢复起来的森林生态系统中生物多样性的改变,尤其是遗传多样性的改变的研究并不多见。研究在浙江省宁波市天童国家森林公园及周边地区选择了5个苦槠种群,采用SSR微卫星标记来分析砍伐对苦槠种群遗传结构的影响。5对多态SSR引物共得到了29个等位基因。种群内维持了较高的遗传多样性,种群间遗传分化程度较低,基因流达8．68。恢复林和成熟林种群的遗传多样性相差不大,以阿育王寺地区恢复种群的最高;表明砍伐对于苦槠种群遗传多样性的影响不大,这与苦槠较强的萌条能力有关。尽管如此,在恢复种群中观察到近期的种群瓶颈,显示出砍伐对种群遗传组成的影响;而在一个成熟林中也观察到种群瓶颈,这是因片断化导致种群变小之故。植被保存最好的天童国家森林公园内苦槠种群的遗传多样性却较低,这可能与成熟林中苦槠优势度较低有关。     

A review on the relationships between plant genetic diversity and ecosystem functioning

全球变化和人类活动导致物种生境的萎缩, 造成很多植物种群数量缩减, 遗传多样性快速丧失。对于物种多样性低的生态系统, 优势种的遗传多样性可能比物种多样性对生态系统功能产生更大的影响。因此, 了解遗传多样性和生态系统功能的关系(GD-EF)及其机制对生物多样性保护、应对环境变化和生态修复具有指导意义。该文综述了植物遗传多样性对生态系统结构(高营养级生物群落结构)和生态系统功能(初级生产力、养分循环和稳定性)的影响及机制、功能多样性对GD-EF的影响、遗传多样性效应和物种多样性效应的比较, 以及GD-EF在生态修复等实际应用的研究进展。最后指出当前研究的不足之处, 以期为后续研究提供参考: 1)还需深入研究GD-EF机制; 2)未评估遗传多样性对生态系统多功能性的影响; 3)不同遗传多样性测度对生态系统功能的影响不明确; 4)缺少长期的和多空间尺度结合的GD-EF实验; 5)遗传多样性效应相对于其他因子的作用不清楚。     

植物遗传多样性与生态系统功能关系的研究进展

全球变化和人类活动导致物种生境的萎缩, 造成很多植物种群数量缩减, 遗传多样性快速丧失。对于物种多样性低的生态系统, 优势种的遗传多样性可能比物种多样性对生态系统功能产生更大的影响。因此, 了解遗传多样性和生态系统功能的关系(GD-EF)及其机制对生物多样性保护、应对环境变化和生态修复具有指导意义。该文综述了植物遗传多样性对生态系统结构(高营养级生物群落结构)和生态系统功能(初级生产力、养分循环和稳定性)的影响及机制、功能多样性对GD-EF的影响、遗传多样性效应和物种多样性效应的比较, 以及GD-EF在生态修复等实际应用的研究进展。最后指出当前研究的不足之处, 以期为后续研究提供参考: 1)还需深入研究GD-EF机制; 2)未评估遗传多样性对生态系统多功能性的影响; 3)不同遗传多样性测度对生态系统功能的影响不明确; 4)缺少长期的和多空间尺度结合的GD-EF实验; 5)遗传多样性效应相对于其他因子的作用不清楚。     

海南岛红树植物海桑遗传多样性的ISSR分析

海桑 (Sonneratia caseolaris)是海桑科红树植物 ,在我国仅天然分布于海南万宁、琼海、文昌等地。采用 ISSR分子标记技术对所有天然种群和海南东寨港红树林自然保护区引种的人工种群共 4个种群 86个个体进行了遗传变异分析。 11个引物共扩增出 2 39条带 ,其中 194条具多态性 ,多态位点百分率为 81.17%。在种群水平上多态位点百分率 4 0 .5 9%～ 5 0 .2 1% ,平均值为4 5 .71%。 Nei的基因多样性、Shannon信息指数在物种水平上分别为 0 .2 10 0和 0 .32 5 6 ,在种群水平上平均值分别为 0 .14 6 8和0 .2 2 10。 Nei的遗传分化系数 Gst和 AMOVA分析表明种群间已发生了较高的遗传分化。种群间的遗传一致度为 0 .90 11。估测的种群间的基因流为 0 .5 787。依据 Nei的遗传距离对不同种群进行 U PGMA聚类 ,聚类结果为横山种群 (HS)和东寨港种群(DZG)聚在一起 ,万宁种群 (WN)和琼海种群 (QH)聚为一类。Mantel检验表明遗传距离与地理距离之间有一定的正相关 ,但不显著。种群遗传多样性与环境因子间的相关性分析表明 :海桑种群遗传多样性水平与各环境因子间相关性均不显著。因东寨港引种种群的遗传多样性明显低于天然种群 ,为保护遗传多样性 ,应加强对琼海、万宁种群的就地保护和迁地保护工作。     

极度濒危植物五针白皮松的保护遗传学研究

用随机扩增多态(RAPD)方法对极度濒危植物五针白皮松(Pinus squamata X.W.Li)的遗传多样性和居群遗传结构进行了研究。14个随机引物共获得93条RAPD谱带,其中6条为多态带,多态位点百分率仅为6．45％,遗传多样性极低。Shannon指数I和Nei指数h在种内也只有0．020和0．030,两个亚居群间(半阴坡亚居群与半阳坡亚居群)遗传分化程度不高,遗传分化系数Gst只有0．110,与大多数松科植物近似,居群每代迁移数为4．032。五针白皮松极低的遗传多样性可能是由于它在演化过程中遭受过严重的灾害,造成严重的瓶颈效应,丧失其大部分遗传变异。在随后的演化过程中由于遗传漂变、自交衰退等小种群现象,导致遗传多样性的进一步丧失。另外,阔叶树种对其生存的挤压和人类的干扰也是导致五针白皮松遗传多样性降低的因素之一。本文最后对该结果的保护生物学意义进行了评价。     

Low genetic diversity and local adaptive divergence of Dracaena cambodiana (Liliaceae) populations associated with historical population bottlenecks and natural selection: an endangered long‐lived tree endemic to Hainan Island,China

Historical population bottlenecks and natural selection have important effects on the current genetic diversity and structure of long‐lived trees. Dracaena cambodiana is an endangered, long‐lived tree endemic to Hainan Island, China. Our field investigations showed that only 10 populations remain on Hainan Island and that almost all have been seriously isolated and grow in distinct habitats. A considerable amount of genetic variation at the species level, but little variation at the population level, and a high level of genetic differentiation among the populations with limited gene flow in D. cambodiana were detected using inter‐simple sequence repeat (ISSR) and random amplified polymorphic DNA (RAPD) analyses. No significant correlation was found between genetic diversity and actual population size, as the genetic diversities were similar regardless of population size. The Mantel test revealed that there was no correlation between genetic and geographic distances among the 10 populations. The UPGMA, PCoA and Bayesian analyses showed that local adaptive divergence has occurred among the D. cambodiana populations, which was further supported by habitat‐private fragments. We suggest that the current genetic diversity and population differentiation of D. cambodiana resulted from historical population bottlenecks and natural selection followed by historical isolation. However, the lack of natural regeneration of D. cambodiana indicates that former local adaptations with low genetic diversity may have been genetically weak and are unable to adapt to the current ecological environments.     

Experimental evaluation of the usefulness of microsatellite DNA for detecting demographic bottlenecks

Evolutionary and conservation biologists often use molecular markers to evaluate whether populations have experienced demographic bottlenecks that resulted in a loss of genetic variation. We evaluated the utility of microsatellites for detection of recent, severe bottlenecks and compared the amounts of genetic diversity lost in bottlenecks of different sizes. In experimental mesocosms, we established replicate populations by releasing 1, 2, 4 or 8 pairs of the western mosquitofish, Gambusia affinis (Poeciliidae). Using eight polymorphic microsatellite loci, we quantified seven indices of genetic diversity or change that have been used to assess the effects of demographic bottlenecks on populations. We compared indices for the experimentally bottlenecked populations to those for the source population and examined differences between populations established with different numbers of founders. Direct count heterozygosity and the proportion of polymorphic loci were not very sensitive to genetic changes that resulted from the experimental bottlenecks. Heterozygosity excess and expected heterozygosity were useful to varying degrees in the detection of bottlenecks. Allelic diversity and temporal variance in allele frequencies were most sensitive to genetic changes that resulted from the bottlenecks, and the temporal variance method was slightly more correlated with bottleneck size than was allelic diversity. Based on comparisons to a previous study with allozymes, heterozygosity, temporal variance in allele frequencies and allelic diversity, but not proportion of polymorphic loci, appear to be more sensitive to demographic bottlenecks when quantified using microsatellites. We found that analysis of eight highly polymorphic loci was sufficient to detect a recent demographic bottleneck and to obtain an estimate of the magnitude of bottleneck severity.     

Population genetics of Mioscirtus wagneri,a grasshopper showing a highly fragmented distribution

The genetic consequences of population fragmentation and isolation are major issues in conservation biology. In this study we analyse the genetic variability and structure of the Iberian populations of Mioscirtus wagneri, a specialized grasshopper exclusively inhabiting highly fragmented hypersaline low grounds. For this purpose we have used seven species‐specific microsatellite markers to type 478 individuals from 24 localities and obtain accurate estimates of their genetic variability. Genetic diversity was relatively low and we detected genetic signatures suggesting that certain populations of M. wagneri have probably passed through severe demographic bottlenecks. We have found that the populations of this grasshopper show a strong genetic structure even at small geographical scales, indicating that they mostly behave as isolated populations with low levels of gene flow among them. Thus, several populations can be regarded as independent and genetically differentiated units which require adequate conservation strategies to avoid eventual extinctions that in highly isolated localities are not likely to be compensated for with the arrival of immigrants from neighbouring populations. Overall, our results show that these populations probably represent the ‘fragments’ of a formerly more widespread population and highlight the importance of protecting Iberian hypersaline environments due to the high number of rare and endangered species they sustain.     

The Kuroshio Current influences genetic diversity and population genetic structure of a tropical seagrass,Enhalus acoroides

Information on genetic diversity and differentiation of seagrass populations is essential for the conservation of coastal ecosystems. However, little is known about the seagrasses in the Indo‐West Pacific Ocean, where the world's highest diversity of seagrasses occurs. The influence of sea currents on these populations is also unknown. We estimated the genetic diversity and population genetic structure and identified reproductive features in Enhalus acoroides populations from the Yaeyama Islands, Hainan Island and the Philippines. The Philippines are situated at the centre of the E. acoroides range, Yaeyama and Hainan are peripheral populations, and the Yaeyama population is at the northern limit of the species range. The powerful Kuroshio Current flows from the Philippines to Yaeyama. Genetic analyses using nine microsatellite markers indicated that reproduction of E. acoroides is mostly sexual. Clonal diversity does not decrease in northern populations, although genetic diversity does. However, the genetic diversity of the Yaeyama populations is greater than that of the Hainan populations. Significant genetic differentiation among most populations was evident; however, the Yaeyama and north‐east Philippines populations were genetically similar, despite being separated by ~1100 km. An assignment test suggested that recruitment occurs from the north‐east Philippines to Yaeyama. The strong current in this region is probably responsible for the extant genetic diversity and recruitment patterns.     

Low genetic diversity and population connectivity fuel vulnerability to climate change for the Tertiary relict pine Pinus bungeana

Endemic species are important components of regional biodiversity and hold the key to understanding local adaptation and evolutionary processes that shape species distributions. This study investigated the biogeographic history of a relict conifer Pinus bungeana Zucc. ex Endl. confined to central China. We examined genetic diversity in P. bungeana using genotyping-by-sequencing and chloroplast and mitochondrial DNA markers. We performed spatial and temporal inference of recent genetic and demographic changes, and dissected the impacts of geography and environmental gradients on population differentiation. We then projected P. bungeana's risk of decline under future climates. We found extremely low nucleotide diversity (average π 0.0014), and strong population structure (global F_ST 0.234) even at regional scales, reflecting long-term isolation in small populations. The species experienced severe bottlenecks in the early Pliocene and continued to decline in the Pleistocene in the western distribution, whereas the east expanded recently. Local adaptation played a small (8%) but significant role in population diversity. Low genetic diversity in fragmented populations makes the species highly vulnerable to climate change, particularly in marginal and relict populations. We suggest that conservation efforts should focus on enhancing gene pool and population growth through assisted migration within each genetic cluster to reduce the risk of further genetic drift and extinction.     

Using pre- and postexploitation samples to assess the impact of commercial whaling on the genetic characteristics of eastern North Pacific gray and humpback whales and to compare methods used to infer historic demography

Many species of whales went through recent bottlenecks due to commercial whaling. These declines were rapid and recent relative to the life spans and generation times of these species, raising questions regarding to what degree commercial whaling influenced the genetic characteristics of these populations. We analyzed mitochondrial and nuclear DNA from pre- and postwhaling samples from two populations that have arguably shown the greatest degree of recovery: eastern North Pacific gray and humpback whales. We also compare the performance of different methods to test for historic bottlenecks and infer past demography based on genetic data. We found substantially higher levels of genetic diversity in gray than in humpback whales (for both time periods), likely due to recent connectivity between Atlantic and Pacific gray whale populations. Other than mitochondrial diversity in humpback whales, levels of diversity were not lower in contemporary samples relative to prewhaling samples, indicating that commercial whaling had a minimal impact on metrics of genetic diversity themselves. However, it did have large impacts on the patterns of diversity, as evidenced by all coalescent-based methods showing clear evidence of a bottleneck for both populations, whereas all but one method not based on the coalescent failed to detect a bottleneck.     

Development of microsatellite primers of the largest seagrass, Enhalus acoroides (Hydrocharitaceae)

? Premise of the study: Microsatellite primers were developed for the seagrass Enhalus acoroides to investigate genetic variation and identify clonal structure. ? Methods and Results: Four polymorphic loci and 32 monomorphic loci were developed in E. acoroides. Two to four alleles per locus were observed at the polymorphic loci across 60 individuals of two E. acoroides populations. The observed and expected heterozygosities within populations ranged from 0.100 to 0.5667 and from 0.0977 to 0.5079, respectively. ? Conclusions: Our study revealed very low polymorphism in E. acoroides, even at the polymorphic loci. Nevertheless, these primers are a useful tool to study genetic variation, clonal structure, and mating system.     

Genetic diversity and genetic structure of Decalobanthus boisianus in Hainan Island,China

Decalobanthus boisianus is a native plant of Hainan Island, China, which has caused considerable damage to tropical forest ecosystems in recent decades. Understanding the genetic diversity and structure of this species can facilitate uncovering the molecular mechanism of its invasive ability. Here, we collected 77 individuals of D. boisianus spanning 8 distribution areas with a gradient of human disturbance intensity (i.e., low, moderate, and high disturbance intensity groups) to assess patterns of genetic diversity and structure using inter simple sequence repeat (ISSR) markers. We found that a total of 220 loci were scored with 13 primers using ISSR methods, and that 198 loci were polymorphic. The genetic diversity of D. boisianus among these eight forests decreased with increasing human disturbance intensity. Over 70% of the total genetic variation was present within populations, while less than 30% of variation was found among populations. There was a high gene flow (1.27) among them due to a lack of effective geographic barriers. The mean Nei's genetic distance of D. boisianus populations was found to be relatively small (i.e., 0.07), and the average genetic similarity of the eight populations was high (i.e., 0.93). Our findings indicate that the genetic diversity of D. boisianus correlated to human disturbance density, and that D. boisianus populations in Hainan Island have frequent gene exchange. We suggest that reduce deforestation to decrease human disturbance may be a good way to prevent the invasion of D. boisianus.     

Genetic diversity and structure of the endangered lady's slipper orchid Cypripedium japonicum Thunb. (Orchidaceae) in Japan

Cypripedium japonicum Thunb. (Orchidaceae), once a common perennial herb, is now designated as endangered throughout most of its distribution due to habitat destruction and fragmentation, and the impacts of horticultural collection. We investigated the genetic characteristics of this species for conservation purposes, using microsatellite markers to examine the genetic diversity and structure of 15 native and 5 ex situ populations in Japan. The results imply that although allelic variation is low in Japanese C. japonicum, sexual reproduction by seed, as well as clonal propagation, may occur in some populations. Both native and ex situ populations were found to be genetically differentiated, indicating that some populations may have experienced recent population declines, genetic fragmentation, or bottlenecks. The degree of genetic drift from the putative ancestral population, inferred through STRUCTURE analysis, was more pronounced in northern populations than in southern populations. Some of the ex situ conserved populations exhibited a low degree of differentiation from ancestral native populations. Our results imply that conservation of C. japonicum in Japan is best supported by maintaining individual populations and their unique genetic characteristics.     

岛屿植物舟山新木姜子居群遗传多样性的RAPD分析

基于随机扩增多态 DNA(RAPD)方法分析了舟山群岛濒危植物舟山新木姜子 (N eolitsea sericea) 6个居群的遗传多样性及分化程度。 10条随机引物扩增出 84个可分析位点 ,多态位点百分比 (PPL)为 3 8.10 %。经 POPOGENE分析发现 ,舟山新木姜子居群平均水平的多态位点百分比 (PPL )为 2 3 .18% ,Nei' s基因多样度 (HE)为 0 .0 793 ,Shannon信息指数 (H )为 0 .12 0 1,与其它岛屿植物比较具有中等偏低水平的遗传多样性 ;岛屿各居群间遗传分化程度较高 (Gst=0 .3 646) ;地理距离与遗传距离之间具有显著相关性 (r=0 .7697,P=96.62 % ) ,岛屿隔离效应是导致居群间遗传分化的重要因素。结合居群遗传多样性及UPGMA聚类分析 ,推测普陀山岛舟山新木姜子部分个体可能为大猫岛迁入的后裔 ,而朱家尖岛舟山新木姜子则由人为移植自普陀山岛。基于舟山新木姜子的物种保护及资源利用 ,建议加强现有自然居群的就地保护 ,促进居群自然更新 ;建立种质资源库 ,收集不同岛屿的种源进行混合繁殖 ,促进基因交流 ;选育优良品系用于海岛植被恢复及园林观赏