Genetic variation in a freshwater bryozoan. I: Populations in the Thames basin, UK

In spite of increasing interest in metapopulation dynamics, the genetic consequences of a metapopulation structure remain poorly understood. Here we examine the metapopulation genetic structure of the colonial, facultatively sexual freshwater bryozoan Cristatella mucedo , in the Thames basin of southern England, UK. Populations from nine sites were sampled and colonies genetically characterized using random amplified polymorphic DNA (RAPD)–PCR. A total of 78 different clones was detected over all sites. Despite the large number of clones, genetic distances among clones both within and among sites were very small. Nonetheless, no clone was present at more than one site even though C. mucedo has an asexual dispersal propagule, and clones strongly clustered by sites. No consistent pattern of clonal structure was evident, with both the number and equitability of clones varying greatly among sites. Although sites were genetically distinct, population genetic regions were absent, and a Mantel test indicated that there was no relationship between geographical distances among sites and genetic distances among populations. Our results indicate that C. mucedo exists as a classical metapopulation in the Thames basin, with dispersal independent of distance and all sites contributing to the genetic diversity of the metapopulation.     

Is the proportion of clonal species higher at higher latitudes in Australia?

We provide a large‐scale quantification of the relationship between latitude and the proportion of species with clonal reproduction. Parasite pressure is thought to be higher at low latitudes, while abiotic stress is thought to be higher at high latitudes. We therefore predicted that there would be a higher proportion of clonal species at high latitudes than at low latitudes. We collected data of 4386 native seed plant species from 446 genera and 99 families present in ABRSFlora of Australia. Species' occurrence records were taken from the Atlas of Living Australia, including 817 450 species‐site combinations spanning 34.5° of latitude. Logistic regression showed that the proportion of clonal species significantly increased with latitude, rising from 3.3% clonal species at 9.25°S to 26.7% clonal species at 43.75°S. The overall average proportion of clonal species in Australian seed plants was 9.4%. This study adds to our growing understanding of dramatic latitudinal gradients in the way plants grow and reproduce. It also reveals that Australian vegetation contains a relatively low proportion of clonally reproducing species.     

污染土壤生物恢复技术

污染土壤生物恢复技术张春桂许华夏姜晴楠（中国科学院沈阳应用生态研究所,１１００１５）ＢｉｏｒｅｍｅｄｉａｔｉｏｎｏｆＣｏｎｔａｍｉｎａｔｅｄＳｏｉｌ．ＺｈａｎｇＣｈｕｎｇｕｉ,ＸｕＨｕａｘｉａ,ＪｉａｎｇＱｉｎｇｎａｎ（ＩｎｓｔｉｔｕｔｅｏｆＡｐｐ...     

Asexual and sexual reproductive strategies in clonal plants

Most plants can reproduce both sexually and asexually (or vegetatively),and the balance between the two reproductive modes may vary widely between and within species.Extensive clonal growth may affect the evolution of life history traits in many ways.First,in some clonal species,sexual reproduction and sex ratio vary largely among populations.Variation in sexual reproduction may strongly affect plant's adaptation to local environments and the evolution of the geographic range.Second,clonal growth can increase floral display,and thus pollinator attraction,while it may impose serious constraints and evolutionary challenges on plants through geitonogamy that may strongly influence pollen dispersal.Geitonogamous pollination can bring a cost to plant fitness through both female and male functions.Some co-evolutionary interactions,therefore,may exist between the spatial structure and the mating behavior of clonal plants.Finally,a trade-off may exist between sexual reproduction and clonal growth.Resource allocation to the two reproductive modes may depend on environmental conditions,competitive dominance,life span,and genetic factors.If different reproductive modes represent adaptive strategies for plants in different environments,we expect that most of the resources should be allocated to sexual reproduction in habitats with fluctuating environmental conditions and strong competition,while clonal growth should be dominant in stable habitats.Yet we know little about the consequence of natural selection on the two reproductive modes and factors which control the balance of the two reproductive modes.Future studies should investigate the reproductive strategies of clonal plants simultaneously from both sexual and asexual perspectives.     

Asexual and sexual reproductive strategies in clonal plants

Most plants can reproduce both sexually and asexually (or vegetatively), and the balance between the two reproductive modes may vary widely between and within species. Extensive clonal growth may affect the evolution of life history traits in many ways. First, in some clonal species, sexual reproduction and sex ratio vary largely among populations. Variation in sexual reproduction may strongly affect plant’s adaptation to local environments and the evolution of the geographic range. Second, clonal growth can increase floral display, and thus pollinator attraction, while it may impose serious constraints and evolutionary challenges on plants through geitonogamy that may strongly influence pollen dispersal. Geitonogamous pollination can bring a cost to plant fitness through both female and male functions. Some co-evolutionary interactions, therefore, may exist between the spatial structure and the mating behavior of clonal plants. Finally, a trade-off may exist between sexual reproduction and clonal growth. Resource allocation to the two reproductive modes may depend on environmental conditions, competitive dominance, life span, and genetic factors. If different reproductive modes represent adaptive strategies for plants in different environments, we expect that most of the resources should be allocated to sexual reproduction in habitats with fluctuating environmental conditions and strong competition, while clonal growth should be dominant in stable habitats. Yet we know little about the consequence of natural selection on the two reproductive modes and factors which control the balance of the two reproductive modes. Future studies should investigate the reproductive strategies of clonal plants simultaneously from both sexual and asexual perspectives. Translated from Acta Phytoecologica Sinica, 2006, 20(1): 174–183 [译自: 植物生态学报]     

Out in the cold – how big and how old? Genetic fingerprinting reveals long‐lived individuals withstand climatic oscillations in the arctic‐alpine

In long‐lived, clonally reproducing species, assessing organism size is a nontrivial endeavour because each genetically distinct entity (genet) may comprise multiple modular units (ramets). Attributes of clonally reproducing populations, such as genet size, longevity and clonal diversity (the number of genets in a population), have significant implications for the persistence of populations over time. In the context of climate change, population persistence contributes to community stability and ecosystem resilience. Do clonal individuals persist through periods of climatic oscillations? Are clonal populations composed of a few large and persistent clones, or do they include clones of different sizes and ages? In this issue, de Witte et al. (2012) present an exciting analysis of clonal diversity and genet longevity in populations of four arctic‐alpine plant species with contrasting life histories: Carex curvula, Dryas octopetala, Salix herbacea and Vaccinium uliginosum. Using amplified fragment length polymorphism (AFLP) data, the authors demonstrate that genet size ranged from a few centimetres to 18 metres and age estimates for the largest genets ranged from 500 to 4900 years. These data reveal that clonally reproducing populations include individuals that have outlived significant changes in climate. Despite the longevity of some individuals, clonal diversity within populations was high, with most individuals existing as small, relatively young genets. Long‐lived individuals, together with high numbers of younger plants, ensure repeated recruitment and population persistence over time. This study represents a novel and timely contribution to a growing body of work aimed at understanding population persistence in changing climates.     

增加水分与养分对克隆植物羊柴自然种群繁殖权衡的影响

 羊柴(Hedysarum laeve)是豆科多年生半灌木,在自然条件下可以同时进行有性繁殖和克隆繁殖。该文在野外条件下研究了不同水平的水分和养 分处理对羊柴种群的繁殖权衡的影响。结果表明,与对照相比,增加一定量的水分处理显著减少了花和荚果的生物量;显著增加了克隆分株枝 的生物量,显著减少了分株根茎的生物量, 但没有影响其它部分的生物量。增加一定量的水分会抑制有性繁殖,改变生物量对克隆繁殖分株各 部分的分配比例。与对照相比,增加一定量的养分能够促进有性繁殖,抑制克隆繁殖。     

Reproductive biology of Clintonia udensis

To clarify the life history of Clintonia udensis, we investigated its reproductive systems and spatio‐temporal population structure. Pollination experiments and the observation of floral visitors revealed that C. udensis was compatible with both self‐ and outcross‐pollen, and it potentially produces seeds by insect‐mediated outcrossing in natural conditions. In addition, propagation by clonal reproduction from rhizomes was evident. In this study, it was clarified that C. udensis potentially propagates by sexual and asexual reproduction and maintains its population through a stable frequency of flowering. The differences in the dependence on each reproduction mode could be one of the contributing factors for creating a variety of population sizes and distribution patterns of ramets in populations.     

Limia vittata as host species for the Amazon molly: no evidence for sexual reproduction

DNA fingerprinting demonstrated no sexual reproduction of the gynogenetic Amazon molly Poecilia formosa with Limia vittata as host species, in contrast with a single report that claims to have found sexual reproduction with such matings.     

Heavy metals modify costs of reproduction and clonal growth in the stoloniferous herb Potentilla anserina

We examined costs of sexual reproduction and clonal propagation, and their consequences for resource allocation in the clonal stoloniferous herb, Potentilla anserina, a typical pioneer species in disturbed areas. We used heavy-metal treatment in soil to create unfavourable growing conditions, because costs of reproduction are more likely to be expressed when resources are limited. We also studied whether heavy metals affect the plasticity of clonal growth form that enables the plants to avoid poor growing conditions. Ramets collected from field were grown in a greenhouse under the heavy-metal treatment consisting of a control and two levels of heavy-metals added in soil. Clonal propagation was costly in terms of total biomass of flowering ramets. Also the costs of sexual reproduction were detected in flowering ramets. Contrary to our predictions, the costs of flower production were visible in the control but not in the heavy-metal contaminated plants. Only the flowering ramets were able to produce longer stolons under heavy-metal stress, but the stolon biomass was not affected by heavy metals. Results indicate that clonal propagation and sexual reproduction may be costly for P. anserina. However, the costs are modified by heavy-metal contamination.Co-ordinating editor: J. Tuomi     

青藏高原及周边高山地区的植物繁殖生态学研究进展

青藏高原及周边高山地区孕育了极为丰富的植物多样性资源,研究该地区植物如何顺利完成繁殖过程有助于我们理解植物对典型高山环境的进化和适应机制。该文综述了青藏高原地区高山植物在资源分配、繁殖方式、花部特征演化等方面的研究进展,包括全球气候变化对植物繁殖特征的影响,以及一些新技术和新方法在本研究领域的应用。在高山地区限制性环境中,随海拔升高,繁殖分配通常表现出增大的趋势,其中投入到雄性资源的比例上升,但具体的资源分配模式还要取决于植株的交配系统、个体大小、生活史特征、遗传特性以及环境中的资源有效性等。面对资源和传粉的双重限制,植物在不同繁殖方式之间存在权衡,当传粉者稀少时,克隆繁殖和自交有利于繁殖保障;而有性繁殖和异交能够提高种子的质量和后代的遗传多样性,从而在复杂多变的气候条件下有利于种群的维持。因此,不同繁殖方式的结合以及泛化的传粉互作网络可能是应对高山限制性环境的最优选择。花部特征的演化主要受到当地传粉者的选择压力,但是外来传粉者、植食者、盗蜜者以及非生物环境(如温度、雨水和紫外辐射等)对花部性状的影响越来越受到重视。近年来,青藏高原因其脆弱性和对气候变化的高度敏感性而在全球气候变化研究中备受关注,以全球变暖和氮沉降增加为显著特征的全球气候变化正在直接或间接地影响着该地区高山植物的繁殖特征。气候变化影响植物和传粉者的物候并引起物种的迁移,最终将导致植物与传粉者的时空不匹配。植物通过改变花部特征(花展示、花冠结构、花报酬的数量和质量)来响应气候变化,这可能会改变其传粉者的类型、数量和访花行为,从而最终影响植物的繁殖成功。3D打印和高通量测序等新技术和新方法的应用有助于促进植物繁殖生态学研究的进一步发展。3D打印的花能够精确控制其形态构造,可以用于研究精细的花部特征变化对于传粉者行为的影响,在此基础上与人工饲养的传粉者结合使用,有助于进一步研究传粉者介导的花部特征演化。随着高通量测序技术的发展,植物繁殖生态学领域,尤其是花部特征演化的许多重要问题的潜在机制得以深入研究。该文最后提出了目前研究中需要注意的问题以及值得深入研究的发展方向。     

The extent of clonality and genetic diversity in the Santa Cruz Island ironwood, Lyonothamnus floribundus

Lyonothamnus floribundus , or island ironwood, is a relictual endemic species found on only four of the eight California Channel Islands. It has been suggested that this species is capable of clonal growth, although the extent of clonality has not been determined. We have used random amplified polymorphic DNA (RAPD) analysis to examine clonality and genetic diversity in L. floribundus . We found that groves are largely genetically distinct clones, indicating that they are not remnants of a once larger clonal forest. Our data also indicate that the population size of L. floribundus on Santa Cruz Island is closer to 1125 individuals, rather than 32 000 based on the number of trunks. The extensive clonality in this species may have a severe impact on its ability to reproduce sexually owing to limitation of pollinator movements among flowers within a single individual. In addition, our data indicate that the two subspecies of L. floribundus are very closely related rather than being two distinct lineages dating to the Miocene, as indicated by the fossil record.