Competitive relationships between two water plant species: Najas marina L. and Myriophyllum spicatum L.

The interrelationships between two submerged macrophytes, Najas marina and Myriophyllum spicatum, were investigated. Double-reciprocal analysis was used to distinguish between the possible types of negative relationships. Results have demonstrated that interspecific inhibition was more severe than the intraspecific one. The intensity of inhibition was negatively correlated with the density of the examined species. The mutual inhibitory effect and the pattern of the obtained results suggest that competitive relationships exist between Najas marina and Myriophyllum spicatum.     

Competitive Interactions between Hydrilla (Hydrilla verticillata) and Vallisneria (Vallisneria americana) as Influenced by Insect Herbivory

Two experiments (winter and summer) were conducted in outdoor tanks using addition-series methods to evaluate the impact of specialized feeding by two biological control agents,Hydrellia pakistanaeDeonier andBagous hydrillaeO'Brien, on competitive interactions between hydrilla [Hydrilla verticillata(L.f.) Royle] and vallisneria (Vallisneria americanaMichx). Competitive abilities of each plant species were determined using the reciprocal-yield model of mean plant weight. In the absence of the biocontrol agents, intraspecific competition from hydrilla on itself was 8.3 times stronger than interspecific competition from vallisneria.Hydrellia pakistanaeinterfered with hydrilla canopy formation by removing as much as 80% of the plant biomass in the top 30 cm of the water column. Damage byH. pakistanaealso caused a 43% reduction in hydrilla tuber production during the winter experiment. Similarly,B. hydrillaecaused up to a 48% reduction in hydrilla plant weight in the summer experiment. Neither insect species damaged vallisneria. As a result, there were significant shifts in the competitive balance between hydrilla and vallisneria due to selective insect feedings. In the presence ofH. pakistanae, hydrilla intraspecific competition was nearly equal to interspecific competition from vallisneria, indicating that hydrilla had lost its competitive edge over vallisneria.Bagous hydrillaealso produced similar, but smaller, shifts in the relative competitive abilities of hydrilla and vallisneria. These results indicate that biological control agents can disrupt the competitive balance between plant species in favor of native species, thus adding another element to the weed biological control strategies.     

Competitive equivalence maintains persistent inter-clonal boundaries

Clear boundaries often separate adjacent conspecific competitors. These boundaries may reflect bordering animal territories or regions of inter-organism contact in mobile and non-mobile organisms, respectively. Sessile, clonal organisms often form persistent inter-clonal boundaries despite great variation in competitive ability among genotypes within a population. I show that neighboring clones in the sea anemone Anthopleura elegantissima and three species of the marine hydroid genus Hydractinia are more evenly matched in terms of competitive ability than expected by chance. Hypotheses of genetic relatedness or similar environmental regime shared by neighboring clones are inconsistent with the observed similarities between adjacent competitors in one or both taxa. Instead, inter-clonal borders evidently persist as standoffs between evenly matched competitors. Large differences in competitive ability between bordering clones were rarely observed, suggesting that dominant clones quickly displace or eliminate others in competitive mismatches. This ecological parallel between taxa (i.e., competitive equivalence) exists despite several fundamental differences (e.g., geographical distribution, habitat, body size, longevity), suggesting that competitive equivalence may be a widespread determinant of boundary persistence between adjacent competitors.     

烟草青枯病劳尔氏菌与拮抗菌对根系分泌物的竞争作用

[目的]研究青枯病病原菌与拮抗菌的营养特性及其对烟草根系分泌物的响应差异,对提高拮抗菌定殖能力、有效生物防控烟草青枯病具有非常重要的意义。[方法]本研究通过筛选与鉴定贵州烟区青枯病病原菌株及拮抗菌株,通过Biolog表型芯片技术分别检测病原菌与拮抗菌的特征性碳、氮源,利用气质联用(GC-MS)检测烟草主栽品种K326根系分泌物的主要物质,在此基础上进行病原菌与拮抗菌对其利用能力、利用强度以及共培养的研究。[结果]经鉴定,分离、筛选到的病原菌株和拮抗菌株分别为青枯劳尔氏菌(Ralstonia solawacearum)和枯草芽孢杆菌(Bacillus subtilis);在含量为0.01μg/mL以上的根系分泌物中,12种物质的含量从高到低排序为:果胶>葡萄糖>木糖>阿拉伯糖>半乳糖>核糖>蔗糖>苯甲酸>果糖=D-甘露醇>棕榈酸>富马酸,果胶含量最高且明显高于其他物质;拮抗菌(LX4)对碳源利用能力高于病原菌(Rs)的碳源有阿拉伯糖、木糖和核糖,分别是病原菌利用能力的1.22、1.95和2.17倍;前12 h拮抗菌利用果糖强度高于病原菌,不同碳源共培养24 h后LX4对gfp-Rs(绿色荧光蛋白标记后的青枯病病原菌)抑制率为18.34%(阿拉伯糖)、53.23%(木糖)、63.53%(核糖)和52.09%(果糖)。[结论]拮抗菌对烟草根系分泌物的利用不及病原菌,但在特定碳源条件下拮抗菌能够利用根系分泌物中的某些碳源产生某种拮抗物质抑制病原菌,拮抗菌与病原菌之间同时存在利用性竞争和干扰性竞争关系,研究结果为进一步研究烟草青枯病的生物防控提供了新的理论依据。     

Comparison of the evolutionary distances among syngens and sibling species of Paramecium

The morphospecies of the genus Paramecium have several mating type groups, so-called syngens, composed of cells of complementary mating types. The Paramecium aurelia complex is composed of 15 sibling species assigned to the species from the syngen. To increase our understanding of the evolutionary relationships among syngen and sibling species of the genus Paramecium, we investigated the gene sequences of cytosol-type hsp70 from 7 syngens of Paramecium caudatum and 15 sibling species of P. aurelia. Molecular phylogenetic trees indicated that the P. aurelia complex could be divided into four lineages and separated into each sibling species. However, we did not find any obvious genetic distance among syngens of P. caudatum, and they could only be separated into two closely related groups. These results indicated that the concept of syngens in P. caudatum differs quite markedly from that of the P. aurelia complex. In addition, we also discuss the relationships among these species and other species, Paramecium jenningsi and Paramecium multimicronucleatum, which were once classified as varieties of P. aurelia.     

Detection of NADPH-diaphorase activity in Paramecium primaurelia

Recently, we showed that Paramecium primaurelia synthesizes molecules functionally related to the cholinergic system and involved in modulating cell-cell interactions leading to the sexual process of conjugation. It is known that nitric oxide (NO) plays a role in regulating the release of transmitter molecules, such as acetylcholine, and that the NO biosynthetic enzyme, nitric oxide synthase (NOS), shows nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity. In this work, we detected the presence of NADPH-d activity in P. primaurelia. We characterized this activity histochemically by examining its specificity for beta-NADPH and alpha-NADH co-substrates, and sensitivity both to variations in chemico-physical parameters and to inhibitors of enzymes showing NADPH-d activity. Molecules immunologically related to NOS were recognized by the anti-rat brain NOS (bNOS) antibody. Moreover, bNOS immunoreactivity and NADPH-d activity sites were found to be co-localized. The non-denaturing electrophoresis, followed by exposure to beta-NADPH or alpha-NADH co-substrates, revealed the presence of a band of apparent molecular mass of about 124 kDa or a band of apparent molecular mass of about 175 kDa, respectively. In immunoblot experiments, the bNOS antibody recognized a single band of apparent molecular mass of about 123 kDa.     

Costs of Predator Avoidance Reduce Competitive Ability of Daphnia

Large-sized Daphnia hyalina×galeata hybrid and small-sized Ceriodaphnia reticulata were raised together for 3 weeks in thermally stratified flow-through tubes ('plankton organ'), in the presence and the absence of fish kairomone, and their relative performance was monitored, as indicated by the populations' growth rates (r). In the kairomone-free medium, D. hyalina grew faster than C. reticulata; the presence of kairomone reversed this ratio, producing relatively higher r in C. reticulata. The simulated fish presence reduced growth in D. hyalina population also when it was separated from the competitor, while growth in C. reticulata was altered by the kairomone only in the presence of Daphnia. It is suggested that costs of surface avoidance in Daphnia can reduce its competitive superiority to small-sized cladocerans, permanently dwelling at the surface.     

Paramecium GPI Proteins: Variability of Expression and Localization

In Paramecium primaurelia, the two major classes of cell surface proteins, the surface antigen (SAg) and the surface GPI proteins (SGPs), are linked to the plasma membrane through a glycosylphosphatidylinositol (GPI) anchor. In the present study, we have characterized the expression of the SGPs in several geographical strains of P. primaurelia and P. tetraurelia at different temperatures, 23 °C and 32 °C. The identification of the expressed SGPs was performed on purified cilia, by establishing the SGP SDS-PAGE profiles under four different conditions: with or without their anchoring lipid, cleaved with a Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (PI-PLC), and either in a reduced or in an unreduced state. This screening revealed the existence of specific sets of ciliary SGPs, as a function of temperature and the geographical origin of the strains. The SGPs the most abundant at 23 °C and 32 °C displayed a rapid turnover. We also looked for the presence of PI-PLC releasable proteins in purified cortices. In addition to the SAg and SGPs, the cortical fraction was shown to contain other PI-PLC releasable proteins, not found in the ciliary fraction, thus localized exclusively in the interciliary region.     

温度对蝇蛹俑小蜂寄生瓜实蝇蛹功能反应的影响

【目的】蝇蛹俑小蜂是很多双翅目害虫的蛹寄生蜂。了解温度对寄生蜂寄生效能的影响是利用寄生蜂控制害虫的重要前提。【方法】实验室条件下设置温度为21、24、27、30、33℃,测定温度对蝇蛹俑小蜂雌蜂寄生瓜实蝇蛹功能反应的影响。蝇蛹俑小蜂对瓜实蝇蛹的功能反应用Michaelis-Menten-Ⅱ型功能反应模型N_a=AN/(F+N)进行拟合。【结果】不同温度下蝇蛹俑小蜂的寄生潜能(A)和寄主半饱和密度(F)不同。当温度在27℃时,其寄生潜能最大;而寄主半饱和密度随着温度升高而降低。【结论】瓜实蝇在瓜地盛发期的栖境温度适宜蝇蛹俑小蜂的寄生。     

辽河源自然保护区油松群落特征及优势种群结构

通过实地踏查,选取辽河源自然保护区内成片的不同年龄的油松天然次生林群落,采用样方法进行群落学特征信息调查,分析研究区的群落区系特征、外貌特征和优势种群结构特征,为油松天然林的保护和抚育管理提供理论依据。结果表明：（1）辽河源自然保护区油松天然次生林群落中共有种子植物41科90属144种,植物种类丰富,具有明显的温带针叶林特征,以地面芽植物为主（60.27%）,中叶植物占优势（82.19%）;区系组成与温带的成分关系最为密切。（2）优势种油松在研究区构成成片的不同林龄的纯林,幼龄林的群落中小径级（Ⅰ~Ⅲ）个体所占比例较高（75%）,随着年龄增加,大径级个体所占比例逐渐增加,成熟林径级呈正态分布,各龄组高度级和冠幅的变化趋势与径级相似。（3）4个龄组幼苗储备都很丰富,均占更新层的58%以上,成熟林中幼苗所占比例达90%,但幼树比例较少,群落的更新状况不佳,但潜在更新能力较强。     

珍稀濒危植物梓叶槭种群径级结构与种内种间竞争关系

该研究对四川省珍稀濒危植物梓叶槭(Acer catalpifolium)种群的主要分布区进行调查,分析梓叶槭种群径级结构与种内和种间的竞争关系,探讨竞争强度与径级和距离之间的关系。结果表明:(1)梓叶槭胸径与树高之间存在显著的幂函数关系;种群径级结构呈正态分布,中小径级树木较多,高径级树木较少。(2)梓叶槭种内和种间竞争强度分别占总竞争强度(222.87)的15.16%和84.84%,说明竞争主要来自种间。(3)梓叶槭与主要伴生种之间的竞争强度大小依次为柳杉桢楠白栎刺楸灯台树桦木杉木厚朴光皮桦;对象木和竞争木距离与竞争指数之间较好地服从指数函数关系,当对象木与竞争木距离小于1m时,竞争指数可达到5.5,随着距离逐渐增加,其竞争指数相应降低,并最终趋于平缓。(4)竞争强度随对象木胸径的增大而减小,当对象木胸径小于20cm时,受到的竞争压力最大,竞争指数最大的分别是梓叶槭与整个林分(234.98)以及梓叶槭与种间(184.01);当对象木胸径小于10cm时,竞争指数均可以达到18;当对象木胸径大于20cm时,竞争强度变化很小且竞争指数较低;竞争强度与对象木胸径服从幂函数关系(CI=AD-B)。(5)模型预测结果表明,随着梓叶槭胸径的增加,竞争指数均越来越小,竞争强度呈降低趋势;当梓叶槭胸径为0~5cm时,梓叶槭与整个林分受到的竞争强度最大,竞争指数为7.14,占总竞争强度的50%;当胸径大于20cm时,竞争指数变化不大;该模型能很好的预测梓叶槭种内和种间竞争强度。     

Competitive interactions between the rotifer Synchaeta oblonga and the cladoceran Scapholeberis kingi Sars

Competition experiments showed that the small cladoceran Scapholeberis kingi rapidly excluded the rotifer Synchaeta oblonga from mixed-species cultures, but was itself unaffected by the presence of S. oblonga. Short-term experiments testing the effect of S. kingi on the survivorship and reproduction of S. oblonga showed that the former imposed a high mortality on the latter, even though shared food resources were abundant. These results indicate that adult S. kingi mechanically interferes with S. oblonga either by ingesting, or by rejecting in a damaged condition, individuals swept into its branchial chamber. In contrast to many other small species of cladocerans, and like large species of Daphnia, S. kingi has the potential to markedly suppress populations of some rotifer species through a combination of interference and exploitative competition.     

Does uptake of Alexandrium fundyense cysts contribute to the levels of PSP toxin found in the sea scallop, Placopecten magellanicus?

Atlantic sea scallops, Placopecten magellanicus, in most areas of the Bay of Fundy, New Brunswick, Canada, have year-round concentrations of paralytic shellfish posioning (PSP) toxins greater than the regulatory concentration of 80 μg STX eq. 100 g⁻¹ wet weight. Scallops (mean shell height of 10.7 cm, age 3–5 years) were collected by SCUBA and individually tagged near Parker Island, Bay of Fundy. Half were hung 2 m below the low tide water level and the remainder were placed on the bottom (11 m depth at low tide) under the scallops held at 2 m. Scallop, water and sediment samples were collected monthly for determination of concentrations of PSP toxins and Alexandrium fundyense.In October, 1993, mean concentrations of PSP toxins in digestive gland, and mantle were 3205 and 1018 μg STX eq. 100 g⁻¹ wet weight, respectively. Eight months later (June 1994), PSP concentrations in digestive glands from the surface and bottom had declined to 504 and 682 μg STX eq. 100 g⁻¹ wet weight, respectively, whereas those in the mantle had declined to 802 and 681 μg STX eq. 100 g⁻¹ wet weight. During July 1994, A. fundyense concentrations observed at Parker Island and offshore were 320 cells l⁻¹ and 14,200 cells l⁻¹, respectively. Subsequently, toxin concentrations in surface and bottom scallop digestive glands increased to 12,720 and 11,408 μg STX eq. 100 g⁻¹ wet weight, whereas concentrations in mantles increased to 2126 and 1748 μg STX eq. 100 g⁻¹ wet weight, respectively. Concentrations of PSP toxins in these tissues in October 1994 were similar to those measured in October 1993. Concentrations of PSP toxin were less than the regulatory concentration in the gonads and non-detectable in adductor muscles of all scallops sampled.There were no statistically significant differences in profiles for uptake and depuration of PSP toxins in scallops held at the surface compared to those from bottom, suggesting that A. fundyense cysts at the concentrations found in the sediment (45 cysts cm⁻³) did not contribute significantly to the year-round presence of PSP toxins within scallop tissues. The year-round occurrence of PSP toxin is probably due to accumulation during summer blooms followed by a very slow rate of depuration.     

川西北高寒地区多年生禾本科人工草地土壤线虫群落动态

为了查明青藏高原地区建植多年生禾本科人工草地对土壤线虫群落的影响及土壤线虫群落随人工草地建植年限增加的变化趋势,以川西北红原县2018年建植的垂穗披碱草样地(Elymus nutans)和老芒麦样地(Elymus sibiricus)为研究对象,以天然草地(Natural grassland)为对照,于2018—2020每年9月对土壤线虫群落、植被和土壤因子等进行连续监测。研究共分离到土壤线虫38470条,隶属于2纲8目65科172属,平均密度2482条/100g干土;食细菌线虫是研究样地的主要营养类群。垂穗披碱草和老芒麦样地的土壤线虫群落组成结构与天然草地间存在明显差异,但差异性随建植年限增加逐渐降低。线虫群落密度和多样性指数在垂穗披碱草、老芒麦和天然草地间均无显著差异。随建植年限增加,土壤线虫群落密度显著上升,Pielou指数显著下降,丰富度和Shannon指数无显著变化;植物寄生线虫密度和比例在第2年显著增加,并成为优势营养类群。线虫群落生态指数在不同草地类型间无显著差异,但垂穗披碱草和老芒麦样地的线虫基础指数随建植年限增加先增加,在第3年时显著降低(P<0.05)。冗余分...     

The membrane skeleton in Paramecium: Molecular characterization of a novel epiplasmin family and preliminary GFP expression results

Previous attempts to identify the membrane skeleton of Paramecium cells have revealed a protein pattern that is both complex and specific. The most prominent structural elements, epiplasmic scales, are centered around ciliary units and are closely apposed to the cytoplasmic side of the inner alveolar membrane. We sought to characterize epiplasmic scale proteins (epiplasmins) at the molecular level. PCR approaches enabled the cloning and sequencing of two closely related genes by amplifications of sequences from a macronuclear genomic library. Using these two genes (EPI-1 and EPI-2), we have contributed to the annotation of the Paramecium tetraurelia macronuclear genome and identified 39 additional (paralogous) sequences. Two orthologous sequences were found in the Tetrahymena thermophila genome. Structural analysis of the 43 sequences indicates that the hallmark of this new multigenic family is a 79 aa domain flanked by two Q-, P- and V-rich stretches of sequence that are much more variable in amino-acid composition. Such features clearly distinguish members of the multigenic family from epiplasmic proteins previously sequenced in other ciliates. The expression of Green Fluorescent Protein (GFP)-tagged epiplasmin showed significant labeling of epiplasmic scales as well as oral structures. We expect that the GFP construct described herein will prove to be a useful tool for comparative subcellular localization of different putative epiplasmins in Paramecium.     

Field evidence and model predictions of butterfly-mediated apparent competition between gentian plants and red ants

In recent spatial models describing interactions among a myrmecophilous butterfly Maculinea rebeli, a gentian Gentiana cruciata and two competing species of Myrmica ant, we predicted that apparent competition should exist between gentians (the food of young M. rebeli caterpillars) and Myrmica schencki, which supports M. rebeli in its final instar. Here we extend and quantify model predictions about the nature of this phenomenon, and relate them to ecological theory. We predict that: (i) Within sites supporting the butterfly, fewer M. schencki colonies occur in sub-areas containing gentians than in identical habitat lacking this plant. (ii) Where G. cruciata and M. schencki do co-exist, the ant colonies will be less than half the size of those living > 1.5 m from gentians; (iii) The turnover of M. schencki colonies will be much greater than that of other Myrmica species in nest sites situated within 1.5 m of a gentian. All three predictions were supported in the field on 3–6 sites in two mountain ranges, although the exact strength of the apparent competition differed from some model predictions. Field data were also consistent with predictions about apparent mutualisms between gentians and other ants. We suggest that apparent competition is likely to arise in any system in which a specialist enemy feeds sequentially on two or more species during its life-cycle, as occurs in many true parasite-host interactions. We also predict that more complex patterns involving other Myrmica species and G. cruciata occur in our system, with apparent competition existing between them in some sub-areas of a site being balanced by apparent mutualism between them in other sub-areas.     

竞争强度变化对针阔混交林红松和水曲柳径向生长的影响

以3种间伐强度处理下(15%,30%和50%)针阔混交林内优势树种红松(Pinus koraiensis)和水曲柳(Fraxinus mandshurica)为研究对象,基于3次复测数据和树轮宽度数据分析不同间伐强度处理下红松和水曲柳的竞争变化特征,探讨竞争环境变化对保留木径向生长的影响。结果表明,1)红松保留木竞争环境发生变化的单木比例随着间伐强度增加而有所下降,但竞争减弱的保留木所占比例与间伐强度正相关,重度间伐样地内竞争减弱的红松保留木所占比例最大达到63%。不同间伐强度下水曲柳保留木竞争环境发生变化的单木比例一致,竞争减弱的单木比例占50%。2)不同竞争环境的水曲柳保留木径向生长趋势基本一致,而红松保留木径向生长变化趋势有所不同。轻度和重度间伐样地内竞争减弱的红松保留木径向生长在间伐后均呈上升趋势,而中度间伐样地内竞争减弱的红松保留木和各样地竞争不变的红松保留木以及不同竞争强度下水曲柳保留木均在2013年和2014年(间伐后2年内)出现生长抑制,而在2015年(伐后第3年)得到促进。3)随着间伐强度上升,自2015年(伐后第3年)竞争减弱的红松保留木径向生长年增量明显增加,显著...     

Vacuolization of target cells: response to microbial toxins

Summary Vacuolization as a marker of microbial activity on cells is a well-known reaction. The phenomenon involves the formation of vacuoles in the cytoplasm of target cells followed by lysis, especially after the action of different cytotoxins. In this review we summarize data on microbial toxic products causing vacuolization of target cells in the light of recent publications, on the basis of the widely described VacA cytotoxin of Helicobacter pylori.