植物边缘种群遗传多样性研究进展

边缘种群指地理分布边缘可检测到的一定数量的同种个体集合,准确评价其遗传多样性对于理解第四纪冰期后气候变化对物种边缘扩展或收缩、遗传资源保护与利用以及物种形成等有重要意义。该文探讨了维持植物边缘种群遗传多样性的进化机制,分析交配系统对物种边缘及其遗传多样性的影响,比较了边缘与中心种群遗传多样性的差异及其形成的生态与进化过程,并探讨了边缘种群遗传多样性与其所在的群落物种多样性的关系及理论基础。该文提出今后研究的重点是应用全基因组序列或转录组基因序列研究前缘-后缘种群之间或边缘-中心种群之间的适应性差异,边缘种群与所在群落其他物种之间相互作用的分子机制,深入解析边缘种群对环境的适应及边缘种群遗传多样性与群落物种多样性关系的生态与进化过程。     

植物边缘种群遗传多样性研究进展

边缘种群指地理分布边缘可检测到的一定数量的同种个体集合, 准确评价其遗传多样性对于理解第四纪冰期后气候变化对物种边缘扩展或收缩、遗传资源保护与利用以及物种形成等有重要意义。该文探讨了维持植物边缘种群遗传多样性的进化机制, 分析交配系统对物种边缘及其遗传多样性的影响, 比较了边缘与中心种群遗传多样性的差异及其形成的生态与进化过程, 并探讨了边缘种群遗传多样性与其所在的群落物种多样性的关系及理论基础。该文提出今后研究的重点是应用全基因组序列或转录组基因序列研究前缘-后缘种群之间或边缘-中心种群之间的适应性差异, 边缘种群与所在群落其他物种之间相互作用的分子机制, 深入解析边缘种群对环境的适应及边缘种群遗传多样性与群落物种多样性关系的生态与进化过程。     

物种生态位构建理论与双点位基因模型应用

物种生态位构建与其进化关系的研究属于生态位理论的新进展。本文就生态位构建理论做出全面的介绍。分别论述了该理论中最基本的定义(什么是生态位构建)。其进化意义(对双点位种群基因模型的分析结果)及生态位构建与环境的相互作用。主要结果有：①物种的生态位构建机制。从进化尺度上具体描述了其通过新陈代谢、活动和选择来确定自身的生态位(包括部分的创建。毁灭);②自然选择与人工选择具有进化方向异向性,生态位构建可能导致进化惯量与进化动量不同的变化规律;③生态位构建能导致有害的等位基因的修复。能支持或消除稳定的多态现象．引起不平衡等。据此．提出对未来工作的3点展望：①由于人类的生态位构建除了所有物种都具有的特性外,文化是其重要的进化源。因此可将该理论应用到人类社会学科中探讨人类的发展进程;②最初提出生态位构建是基于种群水平的,也可将其作用机制放大或缩小至各种不同的尺度研究具体问题;③由于生态位构建中两种进化方向的异向性,所以在现实的生态环境中特别突出人工选择的作用,可为品种选育和人工调控提供理论依据。     

论单基因的分离负荷

本文引进两个配子选择系数、三个基因互作系统及互作跃变函数描述分离负荷,统一了近四十年来的理论纷争,得到如下结果：（1）只有当对两个配子的选择系数相等时,种群才能平衡。对平衡种群,以往关于分离负荷的结论是成立的,而且种群的适宜度保持不变;（2）当两配子选择系数不等时,种群不可能平衡,此时选择下分离负荷从F1代开始逐代减小,种群向杂合子纯合方向进化,从而解释了许多过去不能解释的现象。     

物种分布模型理论研究进展

利用物种分布模型估计物种的真实和潜在分布区,已成为区域生态学与生物地理学中非常活跃的研究领域。然而,到目前为止,这项技术的理论基础仍然存在不足之处,一些关键的生态过程未能被有效纳入到物种分布模型的理论框架中,从而为解释物种分布模型预测的结果带来了诸多困惑。鉴于此,总结了物种分布模型的理论基础;系统探讨了物种分布模型与物种分布区的关系;特别指出了物种分布模型研究中存在的理论问题;重点阐述了物种分布模型未来的发展方向。研究认为,物种分布模型与生态位理论、源-库理论、种群动态理论、集合种群理论、进化理论等具有重要的联系;正确理解物种分布模型的预测结果与物种分布区的关系,有赖于对影响物种分布的3个主要因素(环境条件、物种相互作用与物种迁移能力)做出定量的分离;目前物种分布模型主要存在的问题是未能将物种的相互作用和物种的迁移能力有效纳入到模型的构建过程中;未来物种分布模型的发展应该加强模型背后理论框架的研究,并进一步加强整合物种相互作用过程、种群动态过程、迁移过程和物种进化过程等内容。研究还认为,从更高的理论层次模拟功能群和群落结构将是未来物种分布模型的重要发展方向。     

通过遗传多样性探讨极小种群野生植物的致濒机理及保护策略: 以裸子植物为例

遗传多样性是生物多样性的重要组成部分, 然而由于资源的过度开发利用和生境的破碎化影响了物种的遗传多样性, 甚至威胁到物种的生存适应性和生物多样性。极小种群野生植物是亟待保护的国家重点保护濒危植物,遗传多样性研究对揭示极小种群致濒机理及保护策略具有重要意义。生境破碎化会造成物种遗传多样性降低、种群间分化增加、基因流减少等, 使种群濒危。但在某些物种中, 繁殖特征、进化历史等生物和生态因素的不同也可能造成近期生境破碎化后遗传效应的延迟。裸子植物进化历史悠久, 包含许多孑遗物种, 由于生活史周期长, 遭受生境破碎化后可能短期内显示不出遗传效应的改变, 但长期很难恢复。本文以裸子植物为例综述了濒危植物的遗传多样性研究的案例, 探讨了濒危裸子植物应对环境恶化的维持机制、致濒因素和保护方案, 旨在说明通过遗传多样性研究充分认识极小种群致濒机理对高效保护极小种群野生植物的重要性。     

岛屿生境下黄毛鼠种群的遗传变异

岛屿具有独特的生态系统,常被生态学家和进化生物学家视为研究生物进化的天然实验室,岛屿生物地理学也受到了越来越多科学家的关注。对舟山群岛8个面积不等岛屿的黄毛鼠(Rattus losea)种群进行了调查,分析了8个种群的遗传变异特征,对探讨岛屿理论中的种群动态和种群分化具有重要意义。采用线粒体分子标记技术,利用PCR扩增得到D-loop区基因序列815 bp,在330个黄毛鼠样本中共识别出15个单倍型,平均核苷酸多样性(P_i)为0.001,平均单倍型多样性(H_d)为0.364,表明舟山群岛黄毛鼠种群的遗传多样性较低。Tajima′s D中性检验显示除了小盘峙种群,均为显著负值(P0.01),表明种群受到了自然选择的作用,历史上发生过种群扩张。AMOVE显示,群体间的遗传分化指数平均值为0.745,处于较高的分化水平,表明遗传变异主要来自种群间,占74.5%。基于线粒体D-loop区序列构建的系统发育树和中值网络都表明8个岛屿的黄毛鼠种群起源于两个母系。此外,Mental检验显示不同岛屿种群间的遗传距离与岛屿间地理距离之间存在显著正相关关系(r=0.6077,P=0.004),种群遗传多样性与岛屿面积并未发现显著相关性(r=0.6255,P=0.1840)。研究结果可为岛屿黄毛鼠种群的微观演化以及一些岛屿物种的进化理论提供参考。     

野生动物种群DNA甲基化进展分析

DNA甲基化通常是指胞嘧啶第5位碳原子和甲基基团的共价结合,可调节基因表达程度,参与有机体的重要生命过程,是目前研究最为透彻的表观遗传过程之一。环境变化可以诱导DNA甲基化的变异,这可能是有机体适应新环境的有效途径之一。研究表明,在不同环境下生存的野生动物,其种群内和种群间均存在显著的DNA甲基化差异;同时,相对于遗传多态性水平,野生动物具有更高的表观遗传多态性水平,表明至少有一部分的表观遗传变异独立于遗传变异,这是DNA甲基化具备潜在进化作用的一个先决条件。DNA甲基化变异可能促进了野生动物种群表型多样化,且一些变异的DNA甲基化模式和水平可跨代遗传,可使其快速适应新环境,有助于种群的扩散和进化。这些研究有助于深入理解野生动物种群中非遗传分歧诱导的一些可遗传的表型现象,洞察野生动物种群环境适应性的表观遗传机制,以及DNA甲基化在物种进化中具有的潜在作用,同时我们也对野生动物种群DNA甲基化研究工作的不足进行了探讨和展望,为野生动物种群的表观遗传研究提供理论依据。     

微卫星标记在种群生物学研究中的应用

微卫星是以几个碱基 (一般为 1～ 6个 )为重复单位组成的简单的串联重复序列 ,具有丰度高、多态性高、共显性标记、选择中性、可自动检测等优点。本文着重介绍了微卫星在种群生物学研究中的应用。微卫星位点可以提供具高分辨率的遗传信息 ,这一特点使微卫星既适合于个体水平上的研究 ,又适合于种群水平上的研究。在个体水平上包括个体识别、交配系统和亲本分析、基因流等研究。微卫星是常用的个体识别手段 ,但在克隆植物遗传结构研究方面的应用还很有限 ;微卫星提高了交配系统和亲本分析、基因流等研究的准确性。在种群水平上微卫星可用于遗传结构、有效种群大小、种群的系统发育重建等研究。微卫星在很多物种 (包括珍稀物种 )的遗传结构研究中得到应用 ;利用微卫星标记确定有效种群大小、检测有效种群大小的波动可以促使我们正确理解种群遗传结构动态和种群进化过程 ;微卫星在种群的系统发育重建研究方面有很大的应用潜力。然而微卫星并不是研究所有问题的唯一选择。文中还讨论了在实际工作中应如何正确利用分子标记等问题     

植物与草食动物之间的协同适应及进化

通常协同进化是指一个物种 (或种群 )的遗传结构由于回应于另一个物种 (或种群 )遗传结构的变化而发生的相应改变。广义的理解 ,协同进化是相互作用的物种之间的互惠进化。生物之间、特别是植物与草食动物之间的协同适应与进化 ,已经成为生物进化、生态、遗传等学科十分关注的问题 ,可能成为生物学中各学科研究的交汇点或结点。作者具体阐述了 :(1)生物之间协同进化的研究意义 ,包括对生物学与生态学的价值 ;(2 )生物之间协同进化研究的限制或困难 ,诸如时间、研究对象、进化等级尺度和研究方法的限制 ;(3)植物与草食动物之间协同进化的主要研究对象 (系统 ) ,即昆虫传粉系统、昆虫诱导植物反应系统、种子散布系统、以及大型草食动物采食与植物反应系统 ;(4 )植物与草食动物之间协同进化的主要研究内容 ,包括适应特征 (性状 )——物种的可塑性 ,以及适应机制——物种适应过程与策略两个方面 ;(5 )植物与草食动物之间协同进化研究的存在问题及研究方向     

GENETIC LOAD AND THE MATING SYSTEM IN HOMOSPOROUS FERNS

The mutational genetic load was calculated assuming mutation-selection-inbreeding equilibrium and applied to homosporous ferns. Diploid species with past inbreeding should have a low genetic load while outcrossers should have a high genetic load. These predictions are consistent with the bimodal pattern of genetic load found in 18 diploid homosporous fern species. The prediction that tetraploids should have a low genetic load is also consistent with estimates of genetic load in several species.     

Genetic Effects of a Persistent Bottleneck on a Natural Population of Ornate Box Turtles (Terrapene ornata)

Human activities in the past few hundred years have caused enormous impacts on many ecosystems, greatly accelerating the rate of population decline and extinction. In addition to habitat alteration and destruction, the loss of genetic diversity due to reduced population size has become a major conservation issue for many imperiled species. However, the genetic effects of persistent population bottlenecks can be very different for long-lived and short-lived species when considering the time scale of centuries. To investigate the genetic effects of persistent population bottlenecks on long-lived species, we use microsatellite markers to assess the level of genetic diversity of a small ornate box turtle population that has experienced a persistent bottleneck in the past century, and compare it to a large relatively undisturbed population. The genetic signature of a recent bottleneck is detected by examining the deviation from mutation-drift equilibrium in the small population, but the bottleneck had little effect on its level of genetic diversity. Computer simulations combined with information on population structure suggest that an effective population size of 300, which results in a census population size of 700, would be required for the small population to maintain 90% of the average number of alleles per locus in the next 200 years. The life history of long-lived species could mask the accelerated rate of genetic drift, making population recovery a relatively slow process. Statistical analysis of genetic data and empirical-based computer simulations can be important tools to facilitate conservation planning.     

Parent-offspring regression suggests heritable susceptibility to ectoparasites in a natural population of kittiwake Rissa tridactyla

Little information is available on the genetic variability of host susceptibility to parasites in natural populations despite its importance for the understanding of the evolution of host-parasite interactions. A long-term demographic and epidemiologic survey of a seabird population allowed us to investigate the potential correlation between parent and offspring ectoparasite load, while controlling for various environmental factors. In particular, parasite loads were measured for all individuals (i.e., parents and offspring) when they were nestlings and the effect of the year and breeding cliff were taken into account. The positive correlation found between parent and offspring parasite loads suggests a heritable susceptibility to ectoparasitism by ticks in this host population and that this character has the potential to respond to natural selection.     

Connections between species diversity and genetic diversity

Species diversity and genetic diversity remain the nearly exclusive domains of community ecology and population genetics, respectively, despite repeated recognition in the literature over the past 30 years of close parallels between these two levels of diversity. Species diversity within communities and genetic diversity within populations are hypothesized to co‐vary in space or time because of locality characteristics that influence the two levels of diversity via parallel processes, or because of direct effects of one level of diversity on the other via several different mechanisms. Here, we draw on a wide range of studies in ecology and evolution to examine the theoretical underpinnings of these hypotheses, review relevant empirical literature, and outline an agenda for future research. The plausibility of species diversity–genetic diversity relationships is supported by a variety of theoretical and empirical studies, and several recent studies provide direct, though preliminary support. Focusing on potential connections between species diversity and genetic diversity complements other approaches to synthesis at the ecology–evolution interface, and should contribute to conceptual unification of biodiversity research at the levels of genes and species.     

Do complex population histories drive higher estimates of substitution rate in phylogenetic reconstructions?

Our curiosity about biodiversity compels us to reconstruct the evolutionary past of species. Molecular evolutionary theory now allows parameterization of mathematically sophisticated and detailed models of DNA evolution, which have resulted in a wealth of phylogenetic histories. But reconstructing how species and population histories have played out is critically dependent on the assumptions we make, such as the clock-like accumulation of genetic differences over time and the rate of accumulation of such differences. An important stumbling block in the reconstruction of evolutionary history has been the discordance in estimates of substitution rate between phylogenetic and pedigree-based studies. Ancient genetic data recovered directly from the past are intermediate in time scale between phylogenetics-based and pedigree-based calibrations of substitution rate. Recent analyses of such ancient genetic data suggest that substitution rates are closer to the higher, pedigree-based estimates. In this issue, Navascués & Emerson (2009) model genetic data from contemporary and ancient populations that deviate from a simple demographic history (including changes in population size and structure) using serial coalescent simulations. Furthermore, they show that when these data are used for calibration, we are likely to arrive at upwardly biased estimates of mutation rate.     

Demographic History and Natural Selection Shape Patterns of Deleterious Mutation Load and Barriers to Introgression across Populus Genome

Hybridization and resulting introgression are important processes shaping the tree of life and appear to be far more common than previously thought. However, how the genome evolution was shaped by various genetic and evolutionary forces after hybridization remains unresolved. Here we used whole-genome resequencing data of 227 individuals from multiple widespread Populus species to characterize their contemporary patterns of hybridization and to quantify genomic signatures of past introgression. We observe a high frequency of contemporary hybridization and confirm that multiple previously ambiguous species are in fact F₁ hybrids. Seven species were identified, which experienced different demographic histories that resulted in strikingly varied efficacy of selection and burdens of deleterious mutations. Frequent past introgression has been found to be a pervasive feature throughout the speciation of these Populus species. The retained introgressed regions, more generally, tend to contain reduced genetic load and to be located in regions of high recombination. We also find that in pairs of species with substantial differences in effective population size, introgressed regions are inferred to have undergone selective sweeps at greater than expected frequencies in the species with lower effective population size, suggesting that introgression likely have higher potential to provide beneficial variation for species with small populations. Our results, therefore, illustrate that demography and recombination have interplayed with both positive and negative selection in determining the genomic evolution after hybridization.     

Ecologically relevant stress resistance: from microarrays and quantitative trait loci to candidate genes — A research plan and preliminary results using<Emphasis Type="Italic">Drosophila</Emphasis> as a model organism and climatic and genetic stress as model stresses

We aim at studying adaptation to genetic and environmental stress and its evolutionary implications at different levels of biological organization. Stress influences cellular processes, individual physiology, genetic variation at the population level, and the process of natural selection. To investigate these highly connected levels of stress effects, it is advisable - if not critical - to integrate approaches from ecology, evolution, physiology, molecular biology and genetics. To investigate the mechanisms of stress resistance, how resistance evolves, and what factors contribute to and constrain its evolution, we use the well-defined model systems ofDrosophila species, representing both cosmopolitan species such asD. melanogaster with a known genome map, and more specialized and ecologically well described species such as the cactophilicD. buzzatii. Various climate-related stresses are used as model stresses including desiccation, starvation, cold and heat. Genetic stress or genetic load is modelled by studying the consequences of inbreeding, the accumulation of (slightly) deleterious mutations, hybridization or the loss of genetic variability. We present here a research plan and preliminary results combining various approaches: molecular techniques such as microarrays, quantitative trait loci (QTL) analyses, quantitative PCR, ELISA or Western blotting are combined with population studies of resistance to climatic and genetic stress in natural populations collected across climatic gradients as well as in selection lines maintained in the laboratory.     

Variability of individual genetic load: consequences for the detection of inbreeding depression

Inbreeding depression is a key factor affecting the persistence of natural populations, particularly when they are fragmented. In species with mixed mating systems, inbreeding depression can be estimated at the population level by regressing the average progeny fitness by the selfing rate of their mothers. We applied this method using simulated populations to investigate how population genetic parameters can affect the detection power of inbreeding depression. We simulated individual selfing rates and genetic loads from which we computed fitness values. The regression method yielded high statistical power, inbreeding depression being detected as significant (5?% level) in 92?% of the simulations. High individual variation in selfing rate and high mean genetic load led to better detection of inbreeding depression while high among-individual variation in genetic load made it more difficult to detect inbreeding depression. For a constant sampling effort, increasing the number of progenies while decreasing the number of individuals per progeny enhanced the detection power of inbreeding depression. We discuss the implication of among-mother variability of genetic load and selfing rate on inbreeding depression studies.     

Interactive effects of pesticide exposure and pathogen infection on bee health – a critical analysis

Bees are fundamentally important for pollination services and declines in populations could have significant economic and environmental implications. Pesticide exposure and pathogen infection are recognised as potential stressors impacting upon bee populations and recently there has been a surge in research on pesticide–disease interactions to reflect environmentally realistic scenarios better. We critically analyse the findings on pesticide–disease interactions, including effects on the survival, pathogen loads and immunity of bees, and assess the suitability of various endpoints to inform our mechanistic understanding of these interactions. We show that pesticide exposure and pathogen infection have not yet been found to interact to affect worker survival under field‐realistic scenarios. Colony‐level implications of pesticide effects on Nosema infections, viral loads and honey bee immunity remain unclear as these effects have been observed in a laboratory setting only using a small range of pesticide exposures, generally exceeding those likely to occur in the natural environment, and assessing a highly selected series of immune‐related endpoints. Future research priorities include the need for a better understanding of pesticide effects on the antimicrobial peptide (AMP) component of an individual's immune response and on social defence behaviours. Interactions between pesticide exposure and bacterial and fungal infections have yet to be addressed. The paucity of studies in non‐Apis bee species is a further major knowledge gap.