DNA聚合酶X家族的起源与进化分析

随着DNA聚合酶X家族成员数量的增加,家族内部的系统发育需要重新检查。来自病毒和细胞的DNA聚合酶X家族成员序列第一次被汇编在一起,进行系统发育分析。分析显示：真核生物DNA聚合酶bcta(polβ)是这个家族的祖先基因,可能与昆虫痘病毒(EPv)之间发生过基因的水平转移;DNA聚合酶mu(polμ)基因仅存在于哺乳动物基因组中,是脱氧核苦酸末端转移酶(TdT)的重复基因;这个家族在低等真核生物的种系进化过程中发生了基因丢失。     

APPEARANCE AND SWEEP OF A GENE DUPLICATION: ADAPTIVE RESPONSE AND POTENTIAL FOR NEW FUNCTIONS IN THE MOSQUITO CULEX PIPIENS

Evolution of a new gene function is a fundamental process of adaptation. Gene duplication followed by divergence due to relaxed selection on redundant copies has been viewed as the predominant mechanism involved in this process. At a macroevolutionary scale, evidence for this scenario came from the analysis of sequences of genes families. However, even if several genetic models have described the different potential microevolutionary scenario for a new function to evolve, little is really known about the initial evolutionary dynamics of such processes. We analyze such early dynamics in natural populations of the mosquito Culex pipiens polymorphic for a duplication at Ace.1, a locus involved in insecticide resistance. The date of occurrence and the selective advantages of the duplication were estimated using frequency data. We propose a scenario where the spread of a duplication is driven, from the very beginning, by selection due to insecticide treatment.     

ISOLATION, CHARACTERIZATION, AND CHROMOSOME MAPPING OF AN ACTIN GENE FROM THE PRIMITIVE GREEN ALGA, NANNOCHLORIS BACILLARIS (CHLOROPHYCEAE)

Historically, the genus Nannochloris has been classified using the morphology of cell division, although the mechanics of division remain relatively poorly understood. Nannochloris bacillaris reproduces by binary fission. Microscopic observation with fluorescein isothiocyanate-phalloidin showed that actin filaments localized near the nucleus and appeared as a ring- or beltlike structure in the septum-forming area in the middle of the cell during cell division. In primitive unicellular Chlorophyta such as N. bacillaris, actin is also thought to play important roles in nuclear migration and cell division. The N. bacillaris actin gene has three exons and two introns defined by two exon–intron junctions with splice site consensus sequences. The two introns are located at codons specifying amino acids 3/4 and 47/48. One of these, intron position 3/4, is conserved in the actin gene of Saccharomyces cerevisiae. The actin gene product was predicted to be 378 amino acids long with an estimated molecular weight of 42 kDa. There is only one copy of the actin gene in the N. bacillaris genome. Nannochloris bacillaris has 14 chromosomes that range in size from 230 kb to 3000 kb, and the total size of the genome was estimated to be 20.3 Mb. The actin gene is on either chromosome XI or XII. In a phylogenetic tree based on the actin gene sequence, N. bacillaris diverged before the divergence of Volvox, Chlamydomonas, and higher plants, and very shortly after the radiation of the Rhodophyta.     

EVOLUTIONARY RELATIONSHIPS AMONG MULTIPLE MODES OF CELL DIVISION IN THE GENUS NANNOCHLORIS (CHLOROPHYTA) REVEALED BY GENOME SIZE, ACTIN GENE MULTIPLICITY, AND PHYLOGENY

A single cell divides to multiply, but not all cells follow the same pattern of division. We studied cell division in seven strains from six species belonging to the genus Nannochloris Naumann and classified their modes of cell division into three types: binary fission ( N. bacillaris Naumann), budding ( N. coccoides Naumann), and autosporulation resulting in the formation of two to four daughter cells ( N. maculata Butcher, N . sp. SAG 251-2, N. atomus Butcher CCAP 251/7 and SAG 14.87, and N. eucaryotum [Wilhelm et al.] Menzel and Wild). To determine the evolutionary relationships among these multiple modes of cell division, we investigated the strains' genome sizes, copy number of actin genes, and phylogeny. The genome sizes were determined by counter-clamped homogeneous electric fields electrophoresis and fluorimetry. The genomes are very small and range from 12.6 Mbp ( N. maculata ) to 47.4 Mbp ( N. atomus SAG 14.87). The genomes of Nannochloris species seem to be among the smallest for free-living eukaryotes. Nannochloris bacillaris (binary fission), N. coccoides (budding), Nannochloris sp. (two-cell type of autosporulation), and N. eucaryotum (multicell type of autosporulation) contain a single actin gene, whereas N. maculata (two-cell type of autosporulation) and two strains of N. atomus (two-cell type of autosporulation) contain two actin genes. This suggests that the actin gene was duplicated in this eukaryote, which has a very small genome. Phylogenetic analyses of partial actin gene sequences suggest that autosporulation is the ancestral mode of cell division.     

ELECTROPHORETIC ANALYSIS OF GENETIC VARIATION IN THE CHAROPHYTA. I. GENE DUPLICATION VIA POLYPLOIDY1

Electrophoretic analysis of 12 species of Chara indicates that functional gene duplication via polyploidy has commonly occurred in the genus. Duplication has been followed by differentiation of the loci encoding phosphoglucose isomerase (PGI). This has led directly to generation of substantial levels of genie variation both within and between taxa. A simple genetic model is proposed to account for the large array of PGI phenotypes encountered in natural populations. Constraints imposed by the reproductive biology of members of the genus, such as selfing, appear to have resulted in selective premiums on intrinsic mechanisms of generating genetic variation. Levels of variation in PGI were higher than would be predicted on the basis of charophyte reproductive characteristics; haploid loci segregate approximately two alleles within each species.     

芹菜韧皮部中的肌动蛋白

芹菜韧皮部初步纯化的肌动蛋白,用SDS聚丙烯酸胺凝胶电泳进行分离,得到与兔骨胳肌的肌动蛋白相似的迁移率,其分子量为43 000道尔顿,与免肌肌动蛋白的分子量相一致。韧皮部的G-肌动蛋白聚合成F-肌动蛋白,在电子显微镜下观察到直径5～7nm肌动蛋白的微丝。用兔肌的重酶解肌球蛋白处理并负染后,在电镜下观察到箭头状装饰。韧皮部的F-肌动蛋白能激活兔肌重酶解肌球蛋白ATP酶的活性,酶活性可被激活8倍以上。证明芹菜韧皮部中确实存在肌动蛋白。     

天牛科昆虫高级分类阶元实体的进化研究

本文从生物地理学、形态学、生态学、行为学、生理学、天牛—寄主植物的相互关系、地质学、气候变迁等诸方面,探讨了天牛科高级分类阶元实体的进化证据,提出了各阶元实体进化关系的新假说。研究结果表明,沟胫天牛亚科、锯天牛亚科和天牛亚科可能于侏罗纪在冈瓦纳古陆上分化出来;花天牛亚科和幽天牛亚科于白垩纪在劳亚古陆上分化出来。各亚科的进化顺序有两种可能:(1)沟胫天牛亚科、锯天牛亚科、天牛亚科、花天牛亚科、幽天牛亚科;(2)沟胫天牛亚科、天牛亚科、锯天牛亚科;花天牛亚科、幽天牛亚科。文章最后还讨论了各亚科的系统发育关系。     

天牛科昆虫高级分类阶元实体的进化研究(英文)

本文从生物地理学、形态学、生态学、行为学、生理学、天牛—寄主植物的相互关系、地质学、气候变迁等诸方面,探讨了天牛科高级分类阶元实体的进化证据,提出了各阶元实体进化关系的新假说。研究结果表明,沟胫天牛亚科、锯天牛亚科和天牛亚科可能于侏罗纪在冈瓦纳古陆上分化出来;花天牛亚科和幽天牛亚科于白垩纪在劳亚古陆上分化出来。各亚科的进化顺序有两种可能:(1)沟胫天牛亚科、锯天牛亚科、天牛亚科、花天牛亚科、幽天牛亚科;(2)沟胫天牛亚科、天牛亚科、锯天牛亚科;花天牛亚科、幽天牛亚科。文章最后还讨论了各亚科的系统发育关系。     

毛乌素沙地群落动态中克隆和非克隆植物作用的比较

毛乌素沙地的克隆植物适应当地的沙化环境 ,并对沙化景观具有积极的改造作用。对克隆植物群落和非克隆植物群落内裸地斑块植物入侵的野外对比观测实验表明 ,克隆植物群落内裸地斑块入侵植物所占的格子数显著地大于非克隆植物群落 ,克隆植物可以提高沙化景观的自我恢复能力 ,在沙化景观的恢复重建中是一种值得利用的生物资源。     

毛乌素沙地群落动态中克隆和非克隆植物作用的比较

 毛乌素沙地的克隆植物适应当地的沙化环境,并对沙化景观具有积极的改造作用。对克隆植物群落和非克隆植物群落内裸地斑块植物入侵的野外对比观测实验表明,克隆植物群落内裸地斑块入侵植物所占的格子数显著地大于非克隆植物群落,克隆植物可以提高沙化景观的自我恢复能力,在沙化景观的恢复重建中是一种值得利用的生物资源。     

DISTRIBUTION AND EVOLUTION OF A GLUCOSEPHOSPHATE ISOMERASE DUPLICATION IN THE LEGUMINOSAE

In the common bean, Phaseolus vulgaris, two loci encode cytosolic glucosephosphate isomerase (GPI) subunits, whereas in the garden pea, Pisum sativum, only one locus is expressed. As a working model, we proposed that this change in isozyme number was produced by a gene-duplication event in the lineage leading to Phaseolus after divergence from that leading to Pisum. This model was tested by analyzing the GPI phenotypes in 119 legume genera, representing all three subfamilies and 23 of the 30 tribes of the Papilionoideae. The duplication was detected in 13 of the 20 papilionoid tribes surveyed, including several members of the putatively primitive tribe Sophoreae. Thus, the duplication appears to be an ancient event, a finding incompatible with the initial hypothesis. Instead, gene silencing is postulated to account for the absence of the duplicated phenotype in many tribes, including such advanced groups as Vicieae, Trifolieae, and Cicereae. Furthermore, silencing has occurred numerous times at lower taxonomic levels, including the subtribe Phaseolinae (Phaseoleae), a monophyletic group in which ten genera were found to have duplicated phenotypes and only one (Strophostyles) appeared to have an unduplicated phenotype. Analysis of GPI phenotypes also revealed numerous cases of partial silencing of duplicate loci as well as nearly equal expression of both loci in many, taxonomically widely scattered species. If our revised hypothesis is correct, this latter result implies that most of the subtribes had formed before significant divergence between the GPI isozymes occurred and, thus, that the radiation of the Papilionoideae was rapid relative to the rate of gene silencing.     

中国东北落叶松属植物rbcL 基因的序列分析及系统演化

长白落叶松的分类位置及与兴安落叶松的种间关系, 长期以来未有定论。本研究从大兴安岭、小兴安岭及张广才岭等6 个地点采集实验材料, 对其叶绿体DNA 的rbcL 基因进行PCR-RFLP 分析并测序。结果显示它们的rbcL 基因序列均没有差异, 表明东北地区落叶松属植物有共同起源。在系统演化上, 长白落叶松来自兴安落叶松(Larix gmelinii Rupr.), 应作为兴安落叶松的变种即L.gmelinii Rupr.var.olgensis Ostenfeld et S.Larsen     

PARALLEL EVOLUTION OF LOCAL ADAPTATION AND REPRODUCTIVE ISOLATION IN THE FACE OF GENE FLOW

Parallel evolution of similar phenotypes provides strong evidence for the operation of natural selection. Where these phenotypes contribute to reproductive isolation, they further support a role for divergent, habitat‐associated selection in speciation. However, the observation of pairs of divergent ecotypes currently occupying contrasting habitats in distinct geographical regions is not sufficient to infer parallel origins. Here we show striking parallel phenotypic divergence between populations of the rocky‐shore gastropod, Littorina saxatilis, occupying contrasting habitats exposed to either wave action or crab predation. This divergence is associated with barriers to gene exchange but, nevertheless, genetic variation is more strongly structured by geography than by ecotype. Using approximate Bayesian analysis of sequence data and amplified fragment length polymorphism markers, we show that the ecotypes are likely to have arisen in the face of continuous gene flow and that the demographic separation of ecotypes has occurred in parallel at both regional and local scales. Parameter estimates suggest a long delay between colonization of a locality and ecotype formation, perhaps because the postglacial spread of crab populations was slower than the spread of snails. Adaptive differentiation may not be fully genetically independent despite being demographically parallel. These results provide new insight into a major model of ecologically driven speciation.     

植物多倍体起源与分子进化研究进展

杂交和多倍化是植物最重要的进化方式之一 ,在自然界普遍存在着多倍体物种 ,约 50 %的被子植物和 80 %的蕨类植物进化历史上都曾经历过这种活动 〔1,2〕。在动物界 ,随着大量分子生物学证据的积累 ,有关杂交 -多倍化物种形成的报道也越来越多〔3〕。随着时间的流逝 ,杂种与祖先种在遗传分化上的积累越来越多 ,这使得探讨多倍体物种起源及其进化成为一个极具挑战性的研究领域。早在二十世纪二三十年代 ,生物学家们就对植物多倍体进行了大量的研究 〔4〕,不过 ,由于当时研究方法的限制 ,他们只能在外部形态、生化特性等方面对多倍体植物进行一…     

THE USEFULNESS OF BEHAVIOR FOR PHYLOGENY ESTIMATION: LEVELS OF HOMOPLASY IN BEHAVIORAL AND MORPHOLOGICAL CHARACTERS

It is widely believed that behavior is more evolutionarily labile and/or more difficult to characterize than morphology, and thus that behavioral characters are not as useful as morphological characters for estimating phylogenetic relationships. To examine the relative utility of behavior and morphology for estimating phylogeny, we compared levels of homoplasy for morphological and behavioral characters that have been used in systematic studies. In an analysis of 22 data sets that contained both morphological and behavioral characters we found no significant difference between mean consistency indices (CIs, which measure homoplasy) within data sets for the two types of characters. In a second analysis we compared overall CIs for 8 data sets comprised entirely of behavioral characters with overall CIs for 32 morphological data sets and found no significant difference between the two types of data sets. For both analyses, 95% confidence limits on the difference between the two types of characters indicate that, even if given the benefit of the doubt, morphological characters could not have substantially higher mean CIs than behavioral characters. These results do not support the idea that behavioral characters are less useful than morphological characters for the estimation of phylogeny.     

MORPHOLOGICAL EVOLUTION MEDIATED BY BEHAVIOR IN THE DAMSELFLIES OF TWO COMMUNITIES

Behavior can play a mediating role in determining the selective pressures that influence the evolution of morphological structures. To examine this, I quantified patterns of morphological variation among larvae of Enallagma damselfly species (Odonata: Coenagrionidae) that use different behaviors to avoid the major predators found in each of two communities, lakes with and without fish. Specifically, I quantified the sizes and shapes of the abdomens and caudal lamellae (used for swimming) and legs for three species from fishless lakes and six species from lakes with fish. A preliminary cladistic analysis indicates that species within each lake type are not members of a single clade, which supports the conclusions of previous odonate taxonomists. Previous studies have shown that species in fishless lakes are very active, running and swimming frequently and at high rates of speed in the absence of predators, and they avoid their primary predators, large dragonflies, by swimming. These species have the widest abdomens, the largest caudal lamellae relative to overall body size, and the longest legs of the species studied, which should make them powerful swimmers and runners. Furthermore, species in fishless lakes are morphologically very similar to one another and differ greatly from fish-lake species, although each is more closely related to species in fish lakes. In contrast, species from lakes with fish move very slowly and infrequently in the absence of predators and do not attempt to evade attacking predators. However, despite their behavioral similarity, large interspecific variation in morphology exists among the fish-lake species, and the only morphological patterns were differences associated with membership in the two primary clades identified in the cladistic analysis. A modification of Felsenstein's (1985) method of evolutionary contrasts which allows character change to be isolated along single branches is introduced and is used to reconstruct the evolutionary histories of these characters. This analysis suggests that large increases in caudal lamella size, abdominal segment lengths and widths, and leg length accompany speciation events associated with habitat shifts from fish-lakes to fishless lakes. Following habitat shifts selection pressures exerted by dragonfly predation apparently favored swimming as an escape tactic, which mediated selection pressures onto morphologies used in swimming to increase swimming performance; morphological patterns in extant species reflect this adaptation to a new environment. Mechanisms by which behaviorally mediated selection could have accelerated evolutionary dynamics following founder events are discussed.     

EVOLUTION OF MORPHOLOGICAL NOVELTY: A PHYLOGENETIC ANALYSIS OF GROWTH PATTERNS IN STREPTOCARPUS (GESNERIACEAE)

Abstract.— Streptocarpus shows great variation in vegetative architecture. In some species a normal shoot apical meristem never forms and the entire vegetative plant body may consist of a single giant cotyledon, which may measure up to 0.75 m (the unifoliate type) or with further leaves arising from this structure (the rosulate type). A molecular phylogeny of 87 taxa (77 Streptocarpus species, seven related species, and three outgroup species) using the internal transcribed spacers and 5.8S region of nuclear ribosomal DNA suggests that Streptocarpus can be divided into two major clades. One of these broadly corresponds to the caulescent group (with conventional shoot architecture) classified as subgenus Streptocarpella, whereas the other is mainly composed of acaulescent species with unusual architecture (subgenus Streptocarpus). Some caulescent species (such as S. papangae) are anomalously placed with the acaulescent clade. Available cytological data are, however, completely congruent with the two major clades: the caulescent clade is x = 15 and the acaulescent clade (including the caulescent S. papangae) is x = 16 (or polyploid multiples of 16). The genera Linnaeopsis, Saintpaulia, and Schizoboea are nested within Streptocarpus. The sequenced region has evolved, on average, 2.44 times faster in the caulescent clade than in the acaulescent clade and this is associated with the more rapid life cycle of the caulescents. Morphological variation in plant architecture within the acaulescent clade is homoplastic and does not appear to have arisen by unique abrupt changes. Instead, rosulate and unifoliate growth forms have evolved several times, reversals have occurred, and intermediate architectures are found. An underlying developmental plasticity seems to be a characteristic of the acaulescent clade and is reflected in a great lability of form.     

THE EVOLUTION OF GENES IN BRANCHED METABOLIC PATHWAYS

Simulation models of the evolution of genes in a branched metabolic pathway subject to stabilizing selection on flux are described and analyzed. The models are based either on metabolic control theory (MCT), with the assumption that enzymes are far from saturation, or on Michaelis–Menten kinetics, which allows for saturation and near saturation. Several predictions emerge from the models: (1) flux control evolves to be concentrated at pathway branch points, including the first enzyme in the pathway. (2) When flux is far from its optimum, adaptive substitutions occur disproportionately often in branching enzymes. (3) When flux is near its optimum, adaptive substitutions occur disproportionately often in nonbranching enzymes. (4) Slightly deleterious substitutions occur disproportionately often in nonbranching enzymes. (5) In terms of both flux control and patterns of substitution, pathway branches are similar to those predicted for linear pathways. These predictions provide null hypotheses for empirical examination of the evolution of genes in metabolic pathways.     

线粒体DNA聚合酶的起源与演化

随着新的DNA聚合酶A家族成员的加入,家族内部的系统发育关系需要重新检查,来自大肠杆菌DNA聚合酶I(DNA Pol I)和它的细菌、噬菌体和真核细胞同源物被用来重建这个家族的系统发育史.分析显示:在真核生物演化的不同阶段,线粒体DNA聚合酶基因可能通过水平基因转移方式起源于不同类群的生物.原始真核生物线粒体DNA聚合酶基因可能来源于细菌,植物线粒体DNA聚合酶基因可能从质粒获得,而真菌和动物线粒体DNA聚合酶基因可能起源于T3/T7相关噬菌体.