昆虫同域物种形成机制及检验

从生物学、生态和遗传的角度阐述昆虫同域物种形成过程中涉及到的可能性机制。昆虫同域种的分化与作用于同域初始种群的歧化选择密切相关,歧化选择间接导致种群生态特征和遗传特征的分化,促进同域近缘种群间的生殖隔离。同域物种形成的过程中涉及到性状替换、性选择、同型交配等机制。寄主专化型多见于昆虫同域种的分化过程中,一般以植食性昆虫为主。有关昆虫同域物种形成的检验机制有多种,归纳起来主要包括同型交配的检验、遗传漂流的量化、遗传分化程度和连锁不平衡(LD)的检测、杂交后代适合度的估算等。目前发现在许多昆虫种类中存在同域物种形成的可能性,但是有关其隔离机制并没有得到充分的解释。     

协同物种形成及其生物学意义

自达尔文与华莱士以来的每位生物学家都承认种间生态学作用对进化的意义。1964年,埃利希和雷文提出了协同进化理论。它反映了生态学相关的不同物种之间的相互作用引起的相互进化。这一理论引起了研究者的广泛重视。近年来,随着进化生态研究的深入发展,学者们对进化过程的生态机制以及生态特性与生态关系进化规律、种间生态学作用引起的物种形成有了进一步的认识。本文仅从协同物种形成的概念出发,对协同物种形成的生态机制以及生物学意义作一简要概述。协同物种形成的概念进化在本质上是一种生态过程,是生物与环境、生物与生物之间相互作用的结果。种群分化的生态机制和物种形成的本质在于对生存条件的逐步适应。按照协同进化理论,物种间的相互作用引起的协同适应     

基因流存在条件下的物种形成研究述评:生殖隔离机制进化

物种形成过程是生物多样性形成的基础, 长期以来一直是进化生物学的中心议题之一。传统的异域物种形成理论认为, 地理隔离是物种分化的主要决定因子, 物种形成只有在种群之间存在地理隔离的情况下才能发生。近年来, 随着种群基因组学的发展和溯祖理论分析方法的完善, 种群间存在基因流情况下的物种形成成为进化生物学领域新的研究焦点。物种形成过程中是否有基因流的发生?基因流如何影响物种的形成与分化?基因流存在条件下物种形成的生殖隔离机制是什么?根据已发表的相关文献资料, 作者综述了当前物种形成研究中基因流的时间和空间分布模式、基因流对物种分化的影响以及生殖隔离机制形成等问题, 指出基因流存在条件下的物种形成可能是自然界普遍发生的一种模式。     

被子植物同域物种形成研究进展

同域物种形成是指在缺少地理隔离的情况下分化出新种,相比异域物种形成更为罕见,存在较多的研究空白.该文分析了近十年来与被子植物同域物种形成相关的国内外研究,着重论述同域物种形成的影响因素和种对间的生殖隔离.考虑到历史上的地理隔离难以确定,加之种对间亲缘关系很近,同域物种的判定容易引发争议.其成因可分为生态因素和突变因素:...     

动物物种形成的生殖隔离机制研究进展

物种形成过程及其机制不仅是理解自然界生物多样性现象的关键,也是长期困扰达尔文的“谜中之谜”,是进化生物学研究领域的核心命题之一。物种形成是指新物种从祖先物种中分化出来的演化过程,也是种群间生殖隔离效应或屏障建立的演化过程,对这一过程及其内在遗传机制的探究和揭示是我们理解生物多样性现象的关键所在。本文聚焦于动物类群,系统阐述了动物物种生殖隔离的产生方式及其分子机制,并探讨了目前动物物种生殖隔离相关研究所面临的瓶颈、挑战和潜在机遇,为后续动物物种形成相关研究提供参考和启发。     

物种形成基因及其功能

什么是物种?新物种是如何形成的？这些问题是生命科学研究的重大问题.物种的形成是在生殖隔离的基础上某些新的生物学性状的形成和保留,是生物进化的最基本过程,其实质是基因结构突变的积累与功能的分化. 地理隔离使群体中的基因不能交流,基因突变也会影响个体间交配趣向,从而造成交配隔离或者交配后杂合体的基因组不亲和、杂交不育甚至杂交不活,使不同的群体逐渐分化为新物种. 随着分子生物学与基因组学的飞速发展,进化生物学家已经发现一些与物种形成有关的基因-物种形成基因（speciation genes）,鉴定并了解这些基因的功能,不仅能使我们在分子水平上理解新物种形成的实质和规律、而且对于我们突破种间屏障进行远缘杂交育种也有重要的理论指导意义.本文综述了目前对几个物种形成基因及其功能的研究进展,为该领域的进一步研究提供资料.     

物种形成与进化研究对现代生物工程技术的影响

自达尔文进化沦问世以来,物种的形成与进化一直成为生物学家关注的中心理论研究问题之一。美国生物学家迈耶(Mayer 1942)著的“系统学和物种起源”,英国辛普松(Simpson1944)的“进化速度和方式”和“进化的意义”,美国植物学家史旦宾斯(Stebbins 1957)著的“植物的变异和进化”,以及美国遗传学家杜布赞斯基(Dobzhansky 1941)的“遗传学和物种起源”等是60年代以前生物系统学和细胞遗传学对物种问题研究的总结。他们的研究已经证明动植物     

植物居群的基因流动态及其相关适应进化的研究进展

生物自然居群间的基因流不但可以阻止遗传分化以维持物种的完整性, 而且也能积极响应生物多样化的进程。理解与基因流相关的适应性进化及其内在机理将有助于我们更好地认识生物物种形成和多样化的原始动力以及真正原因。该文通过对植物种内和种间居群基因流动态进行讨论, 阐述了近年来有关植物基因流动态的一些重要理论观念和研究进展, 以期为相关领域动态及趋势研究提供参考。     

植物居群的基因流动态及其相关适应进化的研究进展

生物自然居群间的基因流不但可以阻止遗传分化以维持物种的完整性,而且也能积极响应生物多样化的进程。理解与基因流相关的适应性进化及其内在机理将有助于我们更好地认识生物物种形成和多样化的原始动力以及真正原因。该文通过对植物种内和种间居群基因流动态进行讨论,阐述了近年来有关植物基因流动态的一些重要理论观念和研究进展,以期为相关领域动态及趋势研究提供参考。     

Interpreting the genomic landscape of speciation: a road map for finding barriers to gene flow

Speciation, the evolution of reproductive isolation among populations, is continuous, complex, and involves multiple, interacting barriers. Until it is complete, the effects of this process vary along the genome and can lead to a heterogeneous genomic landscape with peaks and troughs of differentiation and divergence. When gene flow occurs during speciation, barriers restricting gene flow locally in the genome lead to patterns of heterogeneity. However, genomic heterogeneity can also be produced or modified by variation in factors such as background selection and selective sweeps, recombination and mutation rate variation, and heterogeneous gene density. Extracting the effects of gene flow, divergent selection and reproductive isolation from such modifying factors presents a major challenge to speciation genomics. We argue one of the principal aims of the field is to identify the barrier loci involved in limiting gene flow. We first summarize the expected signatures of selection at barrier loci, at the genomic regions linked to them and across the entire genome. We then discuss the modifying factors that complicate the interpretation of the observed genomic landscape. Finally, we end with a road map for future speciation research: a proposal for how to account for these modifying factors and to progress towards understanding the nature of barrier loci. Despite the difficulties of interpreting empirical data, we argue that the availability of promising technical and analytical methods will shed further light on the important roles that gene flow and divergent selection have in shaping the genomic landscape of speciation.     

A guide to the genomics of ecological speciation in natural animal populations

Interest in ecological speciation is growing, as evidence accumulates showing that natural selection can lead to rapid divergence between subpopulations. However, whether and how ecological divergence can lead to the buildup of reproductive isolation remains under debate. What is the relative importance of natural selection vs. neutral processes? How does adaptation generate reproductive isolation? Can ecological speciation occur despite homogenizing gene flow? These questions can be addressed using genomic approaches, and with the rapid development of genomic technology, will become more answerable in studies of wild populations than ever before. In this article, we identify open questions in ecological speciation theory and suggest useful genomic methods for addressing these questions in natural animal populations. We aim to provide a practical guide for ecologists interested in incorporating genomic methods into their research programs. An increased integration between ecological research and genomics has the potential to shed novel light on the origin of species.     

Ernst Mayr and the integration of geographic and ecological factors in speciation

Mayr's best recognized scientific contributions include the biological species concept and the theory of geographic speciation. In the latter, reproductive isolation evolves as an incidental by‐product of genetic divergence between allopatric populations. Mayr noted that divergent natural selection could accelerate speciation, but also argued that gene flow so strongly retards divergence that, even with selection, non‐allopatric speciation is unlikely. However, current theory and data demonstrate that substantial divergence, and even speciation, in the face of gene flow is possible. Here, I attempt to connect some opposing views about speciation by integrating Mayr's ideas about the roles of ecology and geography in speciation with current data and theory. My central premise is that the speciation process (i.e. divergence) is often continuous, and that the opposing processes of selection and gene flow interact to determine the degree of divergence (i.e. the degree of progress towards the completion of speciation). I first establish that, in the absence of gene flow, divergent selection often promotes speciation. I then discuss how population differentiation in the face of gene flow is common when divergent selection occurs. However, such population differentiation does not always lead to the evolution of discontinuities, strong reproductive isolation, and thus speciation per se. I therefore explore the genetic and ecological circumstances that facilitate speciation in the face of gene flow. For example, particular genetic architectures or ecological niches may tip the balance between selection and gene flow strongly in favour of selection. The circumstances allowing selection to overcome gene flow to the extent that a discontinuity develops, and how often these circumstances occur, are major remaining questions in speciation research. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 26–46.     

Conditions for mutation-order speciation

Two models for speciation via selection have been proposed. In the well-known model of ‘ecological speciation’, divergent natural selection between environments drives the evolution of reproductive isolation. In a second ‘mutation-order’ model, different, incompatible mutations (alleles) fix in different populations adapting to the same selective pressure. How to demonstrate mutation-order speciation has been unclear, although it has been argued that it can be ruled out when gene flow occurs because the same, most advantageous allele will fix in all populations. However, quantitative examination of the interaction of factors influencing the likelihood of mutation-order speciation is lacking. We used simulation models to study how gene flow, hybrid incompatibility, selective advantage, timing of origination of new mutations and an initial period of allopatric differentiation affect population divergence via the mutation-order process. We find that at least some population divergence can occur under a reasonably wide range of conditions, even with moderate gene flow. However, strong divergence (e.g. fixation of different alleles in different populations) requires very low gene flow, and is promoted when (i) incompatible mutations have similar fitness advantages, (ii) less fit mutations arise slightly earlier in evolutionary time than more fit alternatives, and (iii) allopatric divergence occurs prior to secondary contact.     

Ancient lakes revisited: from the ecology to the genetics of speciation

Explosive speciation in ancient lakes has fascinated biologists for centuries and has inspired classical work on the tempo and modes of speciation. Considerable attention has been directed towards the extrinsic forces of speciation—the geological, geographical and ecological peculiarities of ancient lakes. Recently, there has been a resurgence of interest in the intrinsic nature of these radiations, the biological characteristics conducive to speciation. While new species are thought to arise mainly by the gradual enhancement of reproductive isolation among geographically isolated populations, ancient lakes provide little evidence for a predominant role of geography in speciation. Recent phylogenetic work provides strong evidence that multiple colonization waves were followed by parallel intralacustrine radiations that proceeded at relatively rapid rates despite long‐term gene flow through hybridization and introgression. Several studies suggest that hybridization itself might act as a key evolutionary mechanism by triggering major genomic reorganization/revolution and enabling the colonization of new ecological niches in ancient lakes. These studies propose that hybridization is not only of little impediment to diversification but could act as an important force in facilitating habitat transitions, promoting postcolonization adaptations and accelerating diversification. Emerging ecological genomic approaches are beginning to shed light on the long‐standing evolutionary dilemma of speciation in the face of gene flow. We propose an integrative programme for future studies on speciation in ancient lakes.     

Genome-wide patterns of divergence during speciation: the lake whitefish case study

The nature, size and distribution of the genomic regions underlying divergence and promoting reproductive isolation remain largely unknown. Here, we summarize ongoing efforts using young (12 000 yr BP) species pairs of lake whitefish (Coregonus clupeaformis) to expand our understanding of the initial genomic patterns of divergence observed during speciation. Our results confirmed the predictions that: (i) on average, phenotypic quantitative trait loci (pQTL) show higher F(ST) values and are more likely to be outliers (and therefore candidates for being targets of divergent selection) than non-pQTL markers; (ii) large islands of divergence rather than small independent regions under selection characterize the early stages of adaptive divergence of lake whitefish; and (iii) there is a general trend towards an increase in terms of numbers and size of genomic regions of divergence from the least (East L.) to the most differentiated species pair (Cliff L.). This is consistent with previous estimates of reproductive isolation between these species pairs being driven by the same selective forces responsible for environment specialization. Altogether, dwarf and normal whitefish species pairs represent a continuum of both morphological and genomic differentiation contributing to ecological speciation. Admittedly, much progress is still required to more finely map and circumscribe genomic islands of speciation. This will be achieved through the use of next generation sequencing data but also through a better quantification of phenotypic traits moulded by selection as organisms adapt to new environmental conditions.     

Selection and genomic differentiation during ecological speciation: isolating the contributions of host association via a comparative genome scan of Neochlamisus bebbianae leaf beetles

This study uses a comparative genome scan to evaluate the contributions of host plant related divergent selection to genetic differentiation and ecological speciation in maple- and willow-associated populations of Neochlamisus bebbianae leaf beetles. For each of 15 pairwise population comparisons, we identified "outlier loci" whose strong differentiation putatively reflects divergent selection. Of 447 AFLP loci, 15% were outliers across multiple population comparisons, and low linkage disequilibrium indicated that these outliers derived from multiple regions of the genome. Outliers were further classified as "host-specific" if repeatedly observed in "different-host" population comparisons but never in "same-host" comparisons. Outliers exhibiting the opposite pattern were analogously classified as "host-independent." Host-specific outliers represented 5% of all loci and were more frequent than host-independent outliers, thus revealing a large role for host-adaptation in population genomic differentiation. Evidence that host-related selection can promote divergence despite gene flow was provided by population trees. These were structured by host-association when datasets included host-specific outliers, but not when based on neutral loci, which united sympatric populations. Lastly, three host-specific outliers were highly differentiated in all nine different-host comparisons. Because host-adaptation promotes reproductive isolation in these beetles, these loci provide promising candidate gene regions for future molecular studies of ecological speciation.