苔藓植物遗传多样性研究现状

苔藓植物具有丰富的遗传多样性 ,本文分别从形态学、细胞学、生化水平和分子水平阐述其遗传多样性的研究现状。     

样方大小对苔藓植物生态学指标的影响

为了分析样方大小对苔藓植物生态指标的影响,在环境相对一致的条件下,在各样点以巢式取样法调查苔藓植物盖度,取样的大小分别为20 cm× 20 cm,30 cm× 30 cm,40 cm×40 cm,50 cm× 50 cm,60 cm×60 cm.通过统计发现,随着取样面积的增加,目测法所获得的优势种、总的苔藓植物的盖度...     

太行花生殖生物学研究Ⅱ有性生殖与无性生殖的调查与研究

通过原产地调查,引种试验,扦插及种子萌发等实验,研究了太行花的繁殖及扩散方式。结果表明,太行花有两条生殖途径：一条是有性生殖;另一条是无性生殖。在原产地因生境条件特殊,有性生殖能力弱,主要靠无性生殖扩大种群。在北京人工栽培条件下,两种生殖方式都能正常进行。     

显著车轮虫无性繁殖生物学研究

显著车轮虫无性繁殖过程中,其新齿环在分裂前期发生于旧齿环和辐线环之间;由细线状圆环分节以覆瓦式排列,其数目常为旧环的一倍,少数个体有增多。随着虫体发育,新环依次长出齿钩、锥体、齿棘。旧环则依齿钩、齿棘、锥体、齿钩柄的顺序消失;口沟、伸缩泡均在分裂前期分裂,各自形成两个新的口沟、伸缩泡;新辐线在子体发育初或中期才发生于新齿环外缘,总数为旧辐线的一倍。该虫无性繁殖以24小时为一周期。分裂前期需0.5—1小时;分裂期需1—3分钟。幼虫生长发育期需1.5—3小时。成虫生长成熟期需20—22小时。无论幼虫、童虫和成虫,均能感染鱼苗并影响其生长发育。     

银杏无性繁殖位置效应的研究

对银杏无性繁殖的位置效应进行了研究。方差分析结果表明,位置效应在无性繁殖过程中能保持稳定,在品种之间有一定差异。随母树及接穗年龄的增长,位置效应越明显。不同无性繁殖方法有相似的位置效应,并具有显著的重现性。在自然状态下,当年生枝条生长的异质性可分为３个枝段。从嫁接到大量结实后,位置效应可经过强－弱－强阶段。采用基生复干作接穗或插条,或用修剪、复壮和扶梢等方法可以控制或消除位置效应,而且效果明显。     

植物无融合生殖研究进展

植物无融合生殖是一种特殊的无性生殖方式 ,它不经过精卵融合即可繁殖后代 ,其二倍体子代基因型与母本精确相同 ,可以固定杂种优势 ,对于作物育种等工作具有巨大的经济意义。对无融合生殖的分类、遗传进化、发生机制、分子机理等方面进行了介绍。并对无融合生殖的一些最新的研究进展 :无孢子生殖专化基因组区、脱调节理论、基因组冲撞观点、表观遗传基因调节理论等进行了简要的评述。并简单介绍了无融合生殖甜菜单体附加系目前的研究进展 。     

The conservation of redundancy in genetic systems: effects of sexual and asexual reproduction

The relationship between probability of survival and the number of deleterious mutations in the genome is investigated using three different models of highly redundant systems that interact with a threatening environment. Model one is a system that counters a potentially lethal infection; it has multiple identical components that act in sequence and in parallel. Model two has many different overlapping components that provide three-fold coverage of a large number of vital functions. The third model is based on statistical decision theory: an ideal detector, following an optimum decision strategy, makes crucial decisions in an uncertain world. The probability of a fatal error is reduced by a redundant sampling system, but the chance of error rises as the system is impaired by deleterious mutations. In all three cases the survival profile shows a synergistic pattern in that the probability of survival falls slowly and then more rapidly. This is different than the multiplicative or independent survival profile that is often used in mathematical models. It is suggested that a synergistic profile is a property of redundant systems. Model one is then used to study the conservation of redundancy during sexual and asexual reproduction. A unicellular haploid organism reproducing asexually retains redundancy when the mutation rate is very low (0001 per cell division), but tends to lose high levels of redundancy if the mutation rate is increased (001 to 01 per cell division). If a similar unicellular haploid organism has a sexual phase then redundancy is retained for mutation rates between 0001 and 01 per cell division. The sexual organism outgrows the asexual organism when the above mutation rates apply. If they compete for finite resources the asexual organism will be extinguished. Variants of the sexual organism with increased redundancy will outgrow those with lower levels of redundancy and the sexual process facilitates the evolution of more complex forms. There is a limit to the extent that complexity can be increased by increasing the size of the genome and in asexual organisms this leads to progressive accumulation of mutations with loss of redundancy and eventual extinction. If complexity is increased by using genes in new combinations, the asexual form can reach a stable equilibrium, although it is associated with some loss of redundancy. The sexual form, by comparison, can survive, with retention of redundancy, even if the mutation rate is above one per generation. The conservation and evolution of redundancy, which is essential for complexity, depends on the sexual process of reproduction.     

Direct evidence for biased gene diversity estimates from dominant random amplified polymorphic DNA (RAPD) fingerprints

The relevance of using dominant random amplified polymorphic DNA (RAPD) fingerprints for estimating population differentiation was investigated when typically small population sample sizes were used. Haploid sexual tissues were first used to determine genotypes at RAPD loci for 75 eastern white pines ( Pinus strobus L.) representing five populations. Dominant RAPD fingerprints were then inferred from genotypic data for each individual at each locus, and gene diversity estimates from both sources of data were compared. Genotypic information at RAPD loci indicated little or no differentiation among populations, similar to allozyme loci. However, estimates of population differentiation derived from dominant RAPD fingerprints according to various common methods of analysis were generally inflated, especially when all fragments were considered. Simulations showed that an increase in loci sampling and population sample sizes did not significantly alleviate the biases observed.     

Adaptive advantages of patterns of growth and asexual reproduction of the sea anemone Metridium senile (L.) in intertidal and submerged populations

Individual size, rate of growth, and mode and frequency of asexual reproduction are life-history traits of primary importance for sea anemones. These traits determine sexual reproductive output, affect an individual's probability of survival, and are crucial in adapting an individual to its environmental surroundings. The sea anemone Metridium senile (L.) is highly variable in ecological distribution and life history, including rate of growth, individual size, and rate of asexual reproduction. Gonad size (measured as cross-sectional area of gonadal tissue) increases with body weight, so individuals should grow as large and as rapidly as possible to maximize individual sexual reproductive output. Cessation of growth and small body size in intertidal populations suggest that growth is constrained by genetic or environmental conditions. The growth of intertidal individuals transplanted to harbor-float panels demonstrated that growth limits are imposed by environmental factors, most probably limited food and feeding time and damage from wave exposure (which stimulates fragmentation). Individuals in harbor-float populations, which are continuously immersed, grow much larger, and large individuals comprise a greater proportion of the population than in the intertidal zone. The highest rate of fragmentation observed was on harbor-float panels. Patterns of growth and asexual reproduction provide adaptive advantages for M. senile. For harborfloat individuals, large individual size increases gamete production and may increase feeding efficiency. For intertidal individuals, asexual reproduction allows growth despite individual size constraints and rapid population growth, with specific advantages resulting from clone formation.     

克隆动物研究进展

本文介绍了世界上和中国采用细胞核移植技术克隆动物的研究历史。综述了细胞核移植的程序、方法和影响因素,包括受体卵母细胞的去核、供体细胞核的制备、核移植、激活、受体细胞与供体细胞的融合、重组胚的体内和体外培养以及胚胎移植产生克隆动物。对克隆动物研究和应用前景进行了讨论。近期的研究结果表明,多代克隆可产生大量遗传性相同的动物,不久的将来克隆技术在商业上的应用将成为现实。     

上海市树附生苔藓植物生态位

生态位理论在植被生态研究中有着重要的应用价值,引入生态位理论对树附生苔藓植物进行了研究。在上海市市区和郊区主要公园、部分街道及校园,包括崇明岛等地区,共设立18个样点,调查发现43种树附生苔藓植物,其中藓类植物39种,苔类植物4种。根据盖度值计算了43种树附生苔藓植物的生态位宽度。结果表明,树附生苔藓植物种数(N)与生态位宽度(B)符合公式N=0.3423e-0.0369B,r=0.9347,大部分的树附生植物生态位宽度很窄,67.44%种类的生态位宽度小于0.1。本文计算了43种树附生苔藓植物的生态位重叠值,应用主分量分析法和最小生成树法对它们进行分类。将43种树附生苔藓植物分成3个生态类群,它们与生境关系显著。因此,在苔藓植物保护中应特别注意对树附生苔藓植物及其生境的保护。     

The gynogenetic reproduction of diploid and triploid hybrid spined loaches (<Emphasis Type="Italic">Cobitis</Emphasis>: Teleostei), and their ability to establish successful clonal lineages—on the evolution of polyploidy in asexual vertebrates

Polyploidisation is assumed to have played a significant role in the evolution of hybrid asexual lineages. The virtual absence of natural asexual systems in which more than a single ploidy level successfully establishes successful independent clonal lineages is generally explained by the strong effects of polyploidisation on fitness. Experimental crosses were made between diploid and triploid asexual Cobitis elongatoides × C. taenia hybrids (female) and both parental spined loach species (male). Genotyping of the progeny using allozymes and multilocus DNA fingerprinting, along with flow cytometric measurement of ploidy level, demonstrated the occurrence of gynogenetic reproduction in both female biotypes. The incorporation of the sperm genome occurred in some progeny, giving rise to a higher ploidy level, but the rate of polyploidisation differed significantly between the diploid and triploid females. These outcomes are consistent with the existence of developmental constraints on tetraploidy, which determine the rarity of tetraploids in natural populations. No cases of ploidy level reduction were observed. Since diploid and triploid hybrid populations occur where the lack of potential progenitor excludes the possibility of de novo origin, it is probable that both diploid and triploid females can establish successful clonal lineages. Spined loaches represent a unique example, among asexual vertebrates, where more than one ploidy level can establish persistent clonal lineages, which are reproductively independent of one another.     

Multiple-scale environmental modulation of lichen reproduction

It is necessary to understand how environmental changes affect plant fitness to predict survival of a species, but this knowledge is scarce for lichens and complicated by their formation of sexual and asexual reproductive structures. Are the presence and number of reproductive structures in Lobaria pulmonaria, a threatened lichen, dependent on thallus size, and is their formation sequential? Does any size-dependence and sequential formation vary along a climate gradient? Generalized linear mixed models were used to explore the effect of environmental predictors on the size and presence/abundance of each reproductive structure and to determine the probability of a given-sized thallus to develop any reproductive structure. The largest individuals are more likely to develop reproductive structures, and the lichen uses a mixed strategy of early asexual reproduction and late sexual. Macro and microclimatic variables also influenced reproductive capacity. Relationships among climate conditions and lichen size and reproductive capacity can compromise the future viability of the species in the most southern populations of Europe.     

The debate about the biological species concept - a review

The importance of the species concept in biology has led to a continuing debate about the definition of species. This paper summarizes the recent literature in relation to the ‘biological species concept’ (MAYR 1942). Among the general attributes demanded, possible limitations of the universality and applicability of a species definition are discussed. Three different areas of criticism of the biological species concept are considered: 1. The impracticability of the criterion of reproductive isolation. The demand for more practical criteria is rejected, because reproductive isolation is seen as the factor that produces and maintains species as discrete entities in nature. 2. The inapplicability to non-bisexual organisms. A brief survey of modes of uniparental reproduction and their relative importance suggests that obligatory apomicts are of little evolutionary significance. 3. The inapplicability to multidimensional situations. Despite practical difficulties, the biological species concept is held to apply to organisms separated in space. The impossibility to delimit species in time by reproductive isolation is recognized. Out of two ways to divide continuous evolutionary lineages in time, the phylogenetic approach, which considers only speciation events (cladogenesis), is preferred as it is more objective. A list of recently published alternative definitions of species, none of which is found acceptable, is given. It is concluded that the biological species concept needs not be changed or dismissed on the basis of the discussed criticisms.     

睡莲无性繁殖栽培技术初探

本文介绍了睡莲属(Nymphaea L.)3个种(延药睡莲N.stellata,黄睡莲N.mexicana,白睡莲N.alba[1])的无性繁殖栽培试验结果,探讨了睡莲无性繁殖栽培技术,为睡莲属植物的快速繁殖奠定了良好的基础。