壶状臂尾轮虫(Brachionus urceus)培养滤液对斜生栅藻(Scenedesmus obliquus)形态和多聚糖含量的影响

分离自太湖的壶状臂尾轮虫(Brachionus urceus (Linnaeus))按1000 ind·L-1的密度置于斜生栅藻(Scenedesmus obliquus)中培养24h后,用孔径0.10 靘的微孔滤膜抽滤,得到壶状臂尾轮虫培养滤液.将壶状臂尾轮虫培养滤液以20%的比例添加到纯培养的斜生栅藻中,进行为期7d的试验.结果表明壶状臂尾轮虫培养滤液能显著地影响斜生栅藻的形态,处理组中诱发性多细胞群体增加,导致处理组中斜生栅藻种群平均每个个体的细胞数量显著高于对照组.斜生栅藻在壶状臂尾轮虫诱发下形成群聚体可以解释为一种诱发性的反牧食防御,同时也进一步证实了栅藻对浮游动物牧食的响应是一种广泛存在的现象.壶状臂尾轮虫培养滤液处理后的斜生栅藻在生长率上与对照组没有显著性差异,说明诱发性防御群聚体形成的代价没有体现在对生长的影响上.在壶状臂尾轮虫培养滤液诱发下,较多栅藻细胞聚积在一起形成群聚体后,栅藻溶解性胞外多聚糖和固着性胞外多聚糖均有显著提高,而胞内多聚糖略有下降.但从总多聚糖含量看,处理组明显高于对照组,这也说明轮虫培养滤液刺激了栅藻多聚糖合成的额外增加,且被分泌到胞外,充当细胞之间的粘合物,促使细胞容易聚合形成群聚体,有效防御象轮虫这些小型浮游动物的进一步牧食,保持种群得以延续.     

食物种类和密度对萼花臂尾轮虫休眠卵形成的影响

采用种群累积培养法,研究了藻类食物的种类和密度对萼花臂尾轮虫休眠卵形成的影响。结果表明,萼花臂尾轮虫的休眠卵主要在开始培养后的６天内形成。在０．１ｍｇ／ｍｌ的食物密度下,与蛋白核小球藻相比,斜生栅藻或斜生栅藻和蛋白核小球藻经１：１（湿重）组成的混合藻均能显著地提高休眠卵的产量和形成效率,同时也使轮虫种群中的平均混交雌体百分率和产休眠卵的混交雌体的平均产卵量明显增大,但对平均混交雌体受精率无显著影响     

食物种类对萼花臂尾轮虫种群增长率的影响

在短期慢性观测过程中,食物类型可能是造成萼花臂尾轮虫(Brachionuscalyciflorus)种群繁殖率变化的一种原因。共观测了分别单独投喂10种不同绿藻对轮虫种群增长率的影响。为验证藻青菌是藻类饵料(如绿藻Scenedesmus)有价值的佐剂这一假说,还用蓝细菌单独投喂或与斜生栅藻(Scenedesmusobliquus)混合投喂轮虫进行实验观测。结果发现食物种类对萼花臂尾轮虫种群增长率影响显著。斜生栅藻组获得最大种群增长(1.6/d),而Desmodesmus组增长率最低(0.3/d)。以占斜生栅藻组最大增长的百分率来表示,其它几种绿藻组种群增长由高到低依次为:Desmodesmussubspicatus88%,小球藻(Chlorellavulgaris)83%,单壳缝藻(Monoraphidiumminutum)77%,D.quadricauda74%,S.falcatus71%,S.acuminatus69%,S.pectinatus64%,莱茵衣藻(Chlamydomonasreinhardtii)57%,D.abundans19%。轮虫增长率的差异不能用藻类饵料的大小差异来解释。蓝细菌(Microcystisaeruginosa)和(Synechococcuselongates)不论是单独投喂还是与优良藻类饵料(斜生栅藻)混合投喂都对萼花臂尾轮虫种群增长有抑制作用。这种副作用似乎与微囊藻素无关。该结果不支持无毒蓝细菌可作为与其他绿藻饵料配合使用的优良佐剂这一假说。本研究所观察到的生长变化显示了饵料种类对萼花臂尾轮虫种群增长的影响,也预示了对毒性实验结果的影响     

三种淡水藻类对萼花臂尾轮虫培养效果的比较

在28℃下,采用群体累积培养法,探讨了不同浓度的蛋白核小球藻（Chlorella pyrenodeosa）、水华鱼腥藻（Anabaena flas-aquae）和沙角衣藻（Chlamyclomoras sajao）,以及在等生物量条件下,以上3种藻类两两配比饵料（3：1、1：1和1：3）对萼花臂尾轮虫（Brachionus calyciflorus）的培养效果。结果表明,不同浓度的蛋白核小球藻、水华鱼腥藻和沙角衣藻对萼花臂尾轮虫增殖效果的影响分别表现为差异极显著（P〈0．01）、显著（P〈0．05）和不显著（P〉0．05）;蛋白核小球藻与水华鱼腥藻组成的混合饵料对萼花臂尾轮虫的增殖效果均优于其中的单一种类（P〈0．05）;沙角衣藻无论是单独投喂,还是与其它藻类混合投喂,轮虫的培养效果均不理想。因此,该种类不宜用作轮虫饵料开发。该研究还表明,蛋白核小球藻是培养萼花臂尾轮虫的最适单一种类,它与水华鱼腥藻组成的混合饵料培养萼花臂尾轮虫效果更好。     

三氯杀螨醇浓度和食物密度对萼花臂尾轮虫种群增长的影响

采用群体累积培养方法,研究了不同浓度(0.03、0.3、3.30和300 μg·L-1)的三氯杀螨醇和不同食物密度(3.0和5.0×106cells·ml-1)的斜生栅藻(Scenedesmus obliquus)对萼花臂尾轮虫(Brachionus calyciflorus)种群增长影响.结果表明:藻类食物密度、三氯杀螨醇浓度以及二者的交互作用对轮虫种群增长率均有显著影响(P＜0.05);藻类食物密度和三氯杀螨醇浓度对轮虫最大种群密度也有显著影响(P＜0.01),但二者的交互作用对其却无显著作用(P＞0.05);与空白对照组相比,在3.0×106cells·ml-1藻密度下.0.03-30μg·L-1的三氯杀螨醇显著提高了轮虫种群增长率,3μg·L-1的三氯杀螨醇显著降低了轮虫的最大种群密度,而300μg·L-1的三氯杀螨醇则极显著提高了轮虫的最大种群密度;在5.0×106cells·ml-1藻密度下,三氯杀螨醇对萼花臂尾轮虫种群增长率和最大种群密度均无显著影响;高密度的藻类食物降低了0.03-30μg·L-1和300μg·L-1的三氯杀螨醇分别对萼花臂尾轮虫种群增长率和最大种群密度所具有的促进作用,以及3μg·L-1的三氯杀螨醇对轮虫最大种群密度所具有的抑制作用.     

斜生栅藻密度对新安江萼花臂尾轮虫种群动态的影响

以浓度分别为1.0×106、2.0×106、4.0×106和8.0×106cells·mL-1的斜生栅藻(Scenedesmus obliquus)为轮虫食物,在25℃下,应用群体累积培养和单个体培养法研究了食物浓度对采自新安江水域(屯溪段)的萼花臂尾轮虫的种群动态影响。结果表明:食物浓度对轮虫的种群增长率和休眠卵产量均有显著的影响,均表现为低食物浓度下(≤4.0×106cells·mL-1)萼花臂尾轮虫的种群增长率和休眠卵产量较小且无差异,高食物浓度下(8.0×106cells·mL-1)轮虫的种群增长率和休眠卵产量较大;食物浓度对轮虫的混交雌体百分率和受精率无显著影响;在食物浓度为4.0×106cells·mL-1时萼花臂尾轮虫的净生殖率最大,世代时间最长,而其内禀增长率在食物浓度为1.0×106cells·mL-1时最小;在食物浓度为8.0×106cells·mL-1时平均寿命和生命期望最长。     

温度和铜绿微囊藻毒性对萼花臂尾轮虫生活史参数的影响

文章开展了25℃下两个品系铜绿微囊藻(有毒与无毒)不同浓度对萼花臂尾轮虫生活史的影响研究, 及在5个温度下不同浓度有毒铜绿微囊藻对萼花臂尾轮虫生活史影响的研究。结果表明铜绿微囊藻毒性、浓度及二者交互作用对轮虫生活史参数净生殖率(R₀; F=31.83, P<0.01; F=30.36, P<0.01; F=13.51, P<0.01)、内禀增长率(r_m; F=34.67, P<0.01; F=18.73, P<0.01; F=12.99, P<0.01)均有显著影响; 温度、铜绿微囊藻浓度及二者交互作用对轮虫生活史参数净生殖率、内禀增长率也均有显著影响。无毒铜绿微藻在低浓度(1×104 cells/mL)下对轮虫种群有促进作用, 可作为轮虫食物来源, 但缺乏脂肪酸等营养物质, 食物质量比蛋白核小球藻低; 在高浓度(1×105和5×105 cells/mL)下轮虫摄食无毒铜绿微囊藻机率变大, 整体食物品质下降, 对轮虫有抑制作用。有毒铜绿微囊藻对轮虫种群的抑制作用更加明显, 微囊藻浓度升高, 净生殖率和内禀增长率显著下降。研究结果还表明30℃和35℃高温下轮虫生长繁殖变快, 世代时间缩短。在高温(30℃和35℃)环境下, 铜绿微囊藻浓度升高对轮虫抑制作用更加明显。     

三个地理品系萼花臂尾轮虫生活史特征的比较

应用单个体培养方法 ,以浓度为 4 0× 10 6 cells ml的斜生栅藻 (Scenedesmusobliquus)为食物 ,在 30℃下 ,对采自广州、芜湖和青岛等地的萼花臂尾轮虫的生活史特征进行了比较研究。结果发现 ,三个地理品系的萼花臂尾轮虫除生殖前期历时无显著差异外 ,其生殖期历时、生殖后期历时、平均寿命和产卵量等均存在显著的差异。轮虫种群的内禀增长率、周限增长率和净生殖率均以芜湖品系最大 ,广州品系最小。这表明若要在 30℃下进行萼花臂尾轮虫的规模化生产 ,芜湖品系应是首选的最适品系     

铜锈环棱螺对水华中常见藻类的抑制效应

藻类水华频发已成为全球性的水环境问题,近年来,生物控藻法因具有环境友好的特点而备受关注。本研究以我国富营养化湖泊中常见大型底栖动物铜锈环棱螺为操纵生物,通过室内培养试验,研究了其对水华水体中常见蓝藻铜绿微囊藻、绿藻普通小球藻和斜生栅藻生长及光合活性的影响,以期阐明螺-藻间相互作用关系,探究铜锈环棱螺作为生物操纵物种的可行性。结果表明: 铜锈环棱螺能在短时间内大量摄食藻细胞,其对铜绿微囊藻产毒株和不产毒株以及斜生栅藻的去除率均在12 h内达到最大值,分别为73.7%、73.2%和51.1%;其对普通小球藻的摄食强于其他藻类,至试验结束时去除率达到99.2%。产毒铜绿微囊藻产生的微囊藻毒素会在铜锈环棱螺体内累积并促发其肝脏病理学变化,进而阻碍铜锈环棱螺的摄食。试验后期各处理组藻细胞光合活性均显著低于对照组,表明铜锈环棱螺的摄食作用对藻细胞造成了损伤,抑制了其大量增殖。此外,当不产毒铜绿微囊藻与斜生栅藻混合时,铜锈环棱螺的选择摄食性导致微囊藻的优势地位被斜生栅藻所取代。因此,铜锈环棱螺可以通过摄食作用抑制藻类的光合活性并降低其生物量,从而在一定程度上抑制或减缓水华的形成。     

铜绿微囊藻对萼花臂尾轮虫与大型溞竞争关系的影响

为探究铜绿微囊藻(Microcystis aeruginosa)浓度变化对浮游动物竞争关系的影响, 通过控制实验法, 评估了在 3个铜绿微囊藻浓度梯度下, 萼花臂尾轮虫(Brachionus calyciflorus)和大型溞(Daphnia magna)之间的种间竞争关系。结果表明不同浓度铜绿微囊藻对萼花臂尾轮虫、大型溞的增长及二者种间竞争影响具有差异, 并且在3种铜绿微囊藻浓度下均以大型溞为主要优势类群。低浓度(5×104 cells/mL)铜绿微囊藻仅促进大型溞种群增长(P<0.01), 大型溞占据主要优势地位; 中浓度(1×105 cells/mL)铜绿微囊藻对萼花臂尾轮虫和大型溞增长均有显著影响(P<0.01), 在此浓度下大型溞在种群竞争中依旧占优势地位, 使得萼花臂尾轮虫种群衰亡; 在高浓度铜绿微囊藻(5×105 cells/mL)环境中种群生长均受到抑制(P<0.01), 在共培养体系中仅大型溞种群存活。在无其他外在影响因素存在时, 实验结果显示在不同浓度的铜绿微囊藻下, 大型溞均占优势, 说明铜绿微囊藻的浓度可能不是影响大型溞与萼花臂尾轮虫的竞争地位的主要因素。研究不同浓度铜绿微囊藻条件下浮游动物种间竞争关系对于理解蓝藻水华暴发的生态效应有重要意义。     

The effect of substances from different zooplankton species and fish on the induction of defensive morphology in the green alga Scenedesmus obliquus

The common green alga Scenedesmus obliquus may respond morphologicallyto the presence of natural enemies. Exposure to water-bornecues from the herbivorous zooplankton Ceriodaphnia reticulata,Daphnia galeata x hyalina, Daphnia magna and Daphnia pulicariastimulated the formation of protective colonies in S. obliquus.This response seemed strongly related to the amount of algaegrazed upon, because a highly significant correlation betweenthe amount of S. obliquus consumed and the induced colony formationwas found. However, when exposed to medium that had been inhabitedby the carnivorous zooplankton Bythotrephes longimanus and Leptodorakindtii, no colony formation occurred. A similar result wasobtained in two different experiments when S. obliquus was exposedto filtrate from cultures of the freshwater fish ide (Leuciscusidus) and perch (Perca fluviatilis). These results support thehypothesis that S. obliquus responds to a herbivorous zooplanktonchemical cue, rather than to a more general animal excretoryproduct. No support was obtained for the hypothesis that cuesfrom the enemy of their enemy could serve as signals to thealgae: despite the presence of filtrate from fish culture, filtratefrom Daphnia cultures induced the formation of colonies in S.obliquus. The biological activity seems to be linked to thealga–grazer interaction, which ensures a reliable cuethat evokes the morphological response of S. obliquus only whennecessary. The grazer-induced colony formation can be viewedas an adaptive reaction in habitats with variable grazing pressurefrom an assemblage of many different herbivores to pare downmortality through grazing.     

食物密度对镜湖萼花臂尾轮虫不同克隆生活史特征的影响

对镜湖萼花臂尾轮虫（Brachionus calyciflorus）夏季种群内4个生化遗传特征上互不相同的克隆（克隆A、B、C和D）在4个斜生栅藻（Scenedesmus obliquus）密度（1.0×10⁶、2.0×10⁶、4.0×10⁶和8.0×10⁶ cells·L^-1）下的生活史特征进行了研究.结果表明：食物密度对各克隆轮虫的存活率和繁殖率均有不同的影响.4克隆中克隆C的世代时间最短,克隆B的世代时间、生命期望和平均寿命最长,克隆A的后代混交雌体百分率最高;净生殖率和个体适合度在4克隆间无显著差异.镜湖萼花臂尾轮虫在2.0×10⁶ cells·L^-1的食物密度下净生殖率最低;在1.0×10⁶cells·L^-1的食物密度下平均寿命和生命期望最短,而后代混交雌体百分率却最高;在8.0×10⁶cells·L^-1的食物密度下种群内禀增长率最高,平均寿命和生命期望最长;在高食物密度（4.0、8.0×10⁶cells·L^-1）下个体适合度较大.克隆C的个体适合度在密度为3.9×10⁶cells·L^-1时最小,而克隆D的个体适合度在食物密度为6.34×10⁶cells·L^-1时最大.食物密度的变化可能是7月份之后镜湖萼花臂尾轮虫从水环境中消失的原因,而4克隆轮虫个体适合度的相似性则可能是镜湖轮虫共存于同一水体的原因之一.     

Morphological Response of Microcystis aeruginosa to Grazing by Different Sorts of Zooplankton

In the experiment we investigated the effect of grazing by different sorts of zooplankton on the induction of defensive morphology in the cyanobacterium Microcystis aeruginosa. The results showed that protozoan flagellate Ochromonas sp. grazing could induce colony formation in M. aeruginosa, whereas M. aeruginosa populations in the control and the grazing treatments of copepod Eudiaptomus graciloides, cladoceran Daphnia magna, and rotifer Brachionus calyciflorus were still strongly dominated by unicells and paired cells and no colony forma occurred. In the protozoan grazing treatment, the proportion of unicells reduced from 83.2% to 15.7%, while the proportion of cells in colonial form increased from 0% to 68.7% of the population at the end of the experiment. The occurrence of a majority of colonial M. aeruginosa being in the treatment with flagellates, indicated that flagellate grazing on solitary cells could induce colony formation in M. aeruginosa. The colonies could effectively deter flagellate from further grazing and thus increase the survival of M. aeruginosa. The colony formation in M. aeruginosa may be considered as an inducible defense against flagellate grazing under the conditions that toxin cannot deter flagellate from grazing effectively.     

浮游动物诱发藻类群体的形成

从研究蓝藻水华形成机理的需要出发,综述了浮游动物的牧食压力对藻类群体形成的诱发作用。指出诱发藻类群体形成的化合物来自牧食性浮游动物对藻类的有效牧食,是藻类群体形成的重要原因之一,而这些诱发性的化合物并不是有关生物体的组成成分,是种间相互作用的结果。藻类群体的形成方式有源于一个母细胞的分裂和业已存在的单细胞的聚合两种方式,栅藻的诱发性群体可能是来自一个母细胞的分裂,而在其它藻类的诱发性群体形成如铜绿微囊藻则可能是业已存在的单细胞的聚合。由于藻类形成群体后能显著降低浮游动物对其牧食速率,因此,这种诱发性群体形成的现象,可以解释为藻类对变化的牧食压力的一种有效的反牧食防御策略,也是两者协同进化的结果。浮游动物对藻类群体形成的重要作用,在研究模拟蓝藻群体及水华形成值得借鉴应用。作者还提出推测,水华蓝藻的群体形成,可能就是在富营养化条件下藻类快速生长,加上浮游动物的牧食压力共同作用下联合驱动的结果,而这种群体形成很可能在积累到一定程度后,结合特定的气象水文等理化因子,就会聚集于水表“爆发”出肉眼可见的水华。因此,开展浮游动物牧食作用对水华蓝藻早期群体形成诱发效应的研究不仅能加深对水华形成的全面认识,而且对于进一步认识藻类的诱发性反牧食防御适应机制、揭示生态系统中生物之间的复杂关系也具有重要的理论意义。     

Changes in food quality of the green alga Scenedesmus induced by Daphnia infochemicals: biochemical composition and morphology

1. The effects of Daphnia infochemicals on the morphology and biochemical composition of Scenedesmus were studied and subsequently their influence on Daphnia life history. Three species of Scenedesmus ( S. acutus, S. obliquus and S. subspicatus ) were tested for Daphnia -induced colony formation. Life history experiments were performed with Daphnia cucullata and D. magna feeding on unicellular or colonial S. acutus.
2. Colony formation was promoted when S. acutus and S. obliquus were exposed to filtered water from a D. magna culture. S. subspicatus did not form colonies when exposed to culture water, but showed some colony formation when exposed to live D. magna.
3. No clear differences were found in total lipid, protein or carbohydrate content between the unicellular and colonial ecomorphs of the three Scenedesmus species. However, fatty acid (FA) concentration and composition were changed. Total FA as a percentage of frozen dry weight (DW) were increased in colonies. The ratio of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) and the ratio of ω3 : ω6 fatty acids decreased in colonies.
4. A short-term grazing experiment with three size classes of Scenedesmus revealed lower clearance rates for small Daphnia when feeding on large colonial Scenedesmus.
5. Life history parameters of both Daphnia species were influenced by food type. The intrinsic rate of population increase ( r) was significantly lower for daphnids feeding on colonies.
6. The negative influence of colonial Scenedesmus on population growth of Daphnia seems to be determined by algal morphology rather than biochemical composition.     

The efficacy of Scenedesmus morphology as a defense mechanism against grazing by selected species of rotifers and cladocerans

Phytoplankton often develop various defense mechanisms in response to zooplankton grazing, such as spines and colonies. While it is now known that increased spine length and cells in a colony of members of the genus Scenedesmus, when zooplankton grazing is intense, helps in reducing zooplankton filtering rates, the effect of these defense mechanisms at the population level has been observed in few studies. Here we present data on the growth rates of four zooplankton species, Brachionus calyciflorus, B. patulus, Ceriodaphnia dubia and Daphnia pulex at two food levels using two species of colony-forming Scenedesmus spp.: S. acutus (cell length = 18.2 ± 0.4 µm; width = 4.2 ± 0.1 µm; average colony length = 90 µm; width: 21 µm) and S. quadricauda (cell length: 21 ± 0.5 width 7.5 ± 0.3 µm; average colony length: 84 µm; width: 30 µm). Whereas S. acutus had no spines, S. quadricauda had spines of 6–10 µm. Population growth experiments of the test rotifers and cladocerans were conducted in 100 ml containers with 50 ml of the medium with test algae. Algae concentrations used were: 13 and 52 mg dw l^–1 of each of the two algal species offered in colonial forms. We used an initial inoculation zooplankter density of 1 ind. ml^–1 for either of the rotifer species and 0.2 ind. ml^–1 for either of the cladoceran species. In all, we had 64 test containers (4 test species of zooplankton × 2 test species of algae × 2 algal densities × 4 replicates). We found a significant effect of algal size on the growth rates of all the four tested species of zooplankton. The population growth rates of zooplankton ranged from –0.58 to 0.66 and were significantly higher on diet of S. acutus than of S. quadricauda. Thus, our study confirms that the larger colony size and the formation of spines in S. quadricauda were effective defenses against grazing by both rotifers and smaller sized cladoceran Ceriodaphnia dubia but that larger-bodied Daphnia pulex could exploit both the algal populations equally.