黑龙江省低额溞属的种类及分布（鳃足纲：双甲目）

本文对黑龙江省低额属Ｓｉｍｏｃｅｐｈａｌｕｓ的种类及分布进行了初步的调查。鉴定出低额９种,即锯顶低额Ｓｉｍｏｃｅｐｈａｌｕｓｓｅｒｒｕｌａｔｕｓ,老年低额Ｓ．ｖｅｔｕｌｕｓ,拟老年低额Ｓ．ｖｅｔｕｌｏｉｄｅｓ,棘爪低额Ｓ．ｅｘｓｆｉｎｏｓｕｓ,西伯利亚低额Ｓ．ｓｉｂｉｒｉｃｕｓ,角壳低额Ｓ．ｌｕｓａｔｉｃｕｓ,微齿低额Ｓ．ｈｉｍａｌａｙｅｎｓｉｓｍｉｃｒｏｄｕｓ,黑龙江低额Ｓ．ｈｅｉｌｏｎｇｊｔａｎｇｅｎｓｉｓ和北安低额Ｓ．ｂｅｉａｎｅｎｓｉｓ。对各种低额的形态特征及分布特点作了概括并编制了种的检索表。对所述各种的模式形态及已获种中雄体的精子形态提供活体照片。对部分低额生活环境中的几种主要因子进行了测试,其结果表明,本属各种多生活在水质清洁溶解氧较高且偏碱的水环境中,其水质多在寡污到β中污之间。     

温度和种间竞争对大型溞种群动态和两性生殖的影响

在20℃、25℃下,将大型溞和老年低额溞分别按7+3(B组),5+5(C组),3+7(D组)的组合进行混合培养,以及用单种培养(10+0(A组),0+10(E组))作为对照,研究了温度和种间竞争对大型溞种群动态和两性生殖的影响.实验结果表明:在混合培养时,大型溞对老年低额溞产生明显的竞争优势.20℃、25℃下,单种培养的老年低额溞最大种群密度分别为大型溞的2.31和1.97,而在混合培养下老年低额溞的种群密度明显低于大型溞,在实验25d后几乎全部死亡.25℃下两种溞的种群密度之间存在极显著的负相关性(C组:r=-0.508,n=30,P<0.01;D组:r=-0.483,n=30,P<0.01).在20℃、单种培养下,大型溞在首次产幼溞时即出现雄体,且种群密度与雄体密度呈显著的相关性(r=0.678,n=24,P<0.01).大型溞的最大雄体密度(106 ind.(200ml)~(-1))和最大雄体比例(36.8%)均出现在20℃、单种培养下.25℃下,大型溞在混合培养的B组和C组首次产幼溞时即出现雄体,且雄体在混合培养B组的比例达28.2%.大型溞在25℃、单种培养下没有产生卵鞍,在混合培养下总计产生66个卵鞍,其中空卵鞍占51.5%,而在20℃、混合培养下没有卵鞍产生.实验结果暗示:在较高的温度下,种间竞争刺激了大型溞雄体的产生和卵鞍的形成,高密度的雄体有助于大型溞孤雌生殖雌体向两性生殖雌体的转化.     

温度和食物浓度对老年低额溞生长与生殖的影响

在20℃和25℃培养温度下研究了3种食物浓度对老年低额(Simocephalus vetulusOF Müller)生长与生殖的影响。结果表明:老年低额有4个幼龄(在20℃、低食物浓度下有5个)和10-13个成龄。成龄的龄期明显高于幼龄,第一成龄的发育时间一般最长。在相同温度下,老年低额的首次怀卵所需时间及各龄期一般随食物浓度的增加而缩短,而各龄的平均体长及其生殖量则呈相反的趋势。在相同的食物条件下,25℃老年低额在生长后期的平均体长明显高于20℃,而各龄期却小于20℃。最大体长是2.82mm,出现在25℃、高食物浓度下的第16龄。老年低额的平均最大生殖量和最大内禀增长率分别为144个和0.41/d,均出现在25℃和高食物浓度下。统计分析显示老年低额的生殖量与体长之间存在显著的相关性。老年低额的食物浓度域值小于1×104cells/mL(Scenedesmus obliquus)。作者探讨了老年低额在渔业生产中作为活体饵料养殖对象的可能性。       

The effects of Anabaena spiroides (Cyanophyceae) exopolysaccharide on copper toxicity to Simocephalus serrulatus (Cladocera, Daphnidae)

1. This work investigated the consumption of a microalgal (Anabaena spiroides) exopolysaccharide by the cladoceran Simocephalus serrulatus (Cladocera, Daphnidae) and its effect on copper toxicity. 2. Total organic carbon concentration was used to quantify the microalgal exopolysaccharide. Both copper‐complexed exopolysaccharides and copper‐free exopolysaccharides were taken up by S. serrulatus. 3. A reduction of free copper ions was obtained in the presence of A. spiroides exopolysaccharide. Copper toxicity (EC₅₀) and zooplankton concentrations were inversely correlated to exopolysaccharide concentration in experimental media. 4. An increase of free copper ions in experimental media was obtained after exopolysaccharide consumption, suggesting that S. serrulatus excreted copper to the surrounding environment.     

中国低额溞属二新种和二新纪录（甲壳纲：双甲目：溞科）

本文描述了中国枝角类科低额属的两个新种：黑龙江低额Ｓｉｍｏｃｅｐｈａｌｕｓｈｅｉｏｎｇｊｉａｎｇｅｎｓｉｓｓｐ．ｎｏｖ．和北安低额Ｓｉｍｏｃｅｐｈａｌｕｓｂｅｉａｎｅｎｓｉｓｂｅｉａｎｅｎｓｉｓｓｐ．ｎｏｖ．及两个中国新记录种．     

Spatial patterns and population dynamics of plant-associated microcrustacea (Cladocera) in an English shallow lake (Little Mere, Cheshire)

Little Mere (Cheshire) is a small (2.7 ha) and shallow (average depth 0.7 m) fertile lake in Cheshire, UK. Nymphaeids cover almost 40 % of its entire surface during the growing season (April to October) and practically all the rest is covered by a mixed community of submerged plants. The lake was intensively sampled for plant-associated Cladocera and zooplankters from April 1998-April 2000. Samples were collected at five sites across the lake, three of them located within lily beds, the other two over submerged plant beds of mixed composition. Specific sampling techniques were developed for floating lily leaves, petioles, submerged plants and water. Significant horizontal differences were identified for most cladoceran species, both open-water and plant-associated, for chydorid periphyton scrapers and for filter-feeders. Daphnia hyalina (L.) and Ceriodaphnia sp were significantly more abundant in lily beds than in more open water in both growing seasons, suggesting lily beds are an effective refuge against fish predation. Size-structure and egg-ratio data support this contention. Egg-ratio models were examined for Daphnia hyalina and Simocephalus vetulus (O.F. Müller), a plant-associated cladoceran. The fertility of S. vetulus in lily beds was generally high throughout growing seasons. The construction of egg-ratio models for this species was hampered by their generally very patchy distributions.     

Comparative histopathology of some Diptera and Crustacea of aquatic alpine ecosystems, after treatment with Bacillus thuringiensis var. israelensis

Species of Diptera (larval Culicidae, Chironomidae and Simuliidae) and Crustacea (cladoceran adults) that are representative of the fauna of aquatic alpine ecosystems are routinely treated with Bacillus thuringiensis var. israelensis (Bti) for mosquito control. The toxicity of Bti on these organisms was investigated. Bioassays indicated that Bti used at the concentration for operational field application is deleterious to all dipteran species, but not to Cladocera. Histopathological observations reveal that, in all cases, the midgut epithelium is affected by Bti treatment. However, the vulnerability of epithelial cells to the microbial insecticide is different from one cell-type to another, clear cells being more vulnerable than dark cells. Because of the concentration of clear cells within the anterior midgut of dipteran larvae, this region appears to be the first to show symptoms of intoxication through enhancing a natural process of cell turnover. The relative importance of such a vulnerable region in the midgut of dipteran larvae may account for the general efficacy of Bti to these species. Its harmlessness to Cladocera may be correlated to the relative scarcity of clear cells and their patchy distribution along the whole midgut together with important cellular renewal capacity of the epithelium.     

Lifetable demography of four cladoceran species in relation to algal food (Chlorella vulgaris) density

Algal food density is known to influence life history variables of cladoceran species. It is not, however, well established whether both littoral and planktonic cladocerans show similar trends when exposed to increasing food concentrations. In the present work, we studied the life table demography of four cladoceran species (Ceriodaphnia cornuta, Moina macrocopa, Pleuroxus aduncus and Simocephalus vetulus) in relation to three algal food concentrations (low: 0.5 × 10⁶, medium: 1.5 × 10⁶ and high: 4.5 × 10⁶ cells ml^–1 of Chlorella vulgaris) (in terms of carbon content, these were equivalent to 0.15, 0.45 and 1.35 g ml^–1, respectively) at 25 °C. In general, for all the tested cladoceran species, values of average lifespan, gross reproductive rate, net reproductive rate, generation time and the rate of population growth were higher at lower food concentrations. Furthermore, high food concentration resulted in a negative population growth rate (mean ± standard error: –0.091 ± 0.026) for P. aduncus. The highest population growth rate (0.602 ± 0.014) was recorded for M. macrocopa at low food density. S. vetulus had the longest average lifespan (40 ± 1 d) while M. macrocopa had the lowest (5 ± 1 d). C. cornuta showed better performance at medium food concentration. We conclude that among the algal concentrations used here, 0.5 × 10⁶ – 1.5 × 10⁶ was beneficial not only to the planktonic species but also to the littoral P. aduncus and S. vetulus while 4.5 × 10⁶ cells ml^–1 was unsuitable for all the cladocerans tested.     

Adaptive microevolutionary responses to simulated global warming in Simocephalus vetulus: a mesocosm study

Although several studies suggest the occurrence of microevolutionary responses that may allow local persistence of populations under global warming, rigorous experimental proof is lacking. Here, we combined the realism and rigid, replicated experimental design of a large‐scale mesocosm study where populations of the zooplankter Simocephalus vetulus were exposed for 1 year to different global warming scenarios with a life table experiment under laboratory conditions at three temperatures that eliminated confounding, nongenetic factors. Our results provide solid proof for a rapid microevolutionary response to global warming in both survival and the subcomponents of individual performance (age at reproduction and number of offspring), which may allow populations of S. vetulus to persist locally under predicted scenarios of global warming. Such microevolutionary responses may buffer changes in community structure under global warming and help explain the outcome of previous mesocosm studies finding only marginal effects of global warming at the community level.