Combined effect of concentrations of algal food (Chlorella vulgaris) and salt (sodium chloride) on the population growth of Brachionus calyciflorus and Brachionus patulus (Rotifera)

Salinity is an important variable influencing the density and diversity of rotifers. Studies on salt tolerance of rotifers have so far concentrated on euryhaline species while very little information is available on non-euryhaline taxa. In the present work, we have evaluated the combined effects of Chlorella vulgaris and sodium chloride on the population growth of two freshwater rotifers B. calyciflorus and B. patulus. A 24 hr acute tolerance test using NaCl revealed that B. calyciflorus was more resistant (LC50 = 3.75 +/- 0.04 g l-1) than B. patulus (2.14 +/- 0.09 g l-1). The maximal population density (mean +/- standard error) for B. calyciflorus in the control at 4.5 x 10(6) cells ml-1 (algal level) was 80 +/- 5 ind. ml-1, which was nearly a fifth of the one for B. patulus (397 +/- 7 ind. ml-1) under comparable conditions. Data on population growth revealed that regardless of salt concentration, the density of B. calyciflorus increased with increasing food levels, while for B. patulus, this trend was evident only in the controls. Regardless of salt concentration and algal food level, the day of maximal population density was lower (4 +/- 0.5 days) for B. calyciflorus than for B. patulus (11 +/- 1 day). The highest rates of population increase (r values) for B. calyciflorus and B. patulus were 0.429 +/- 0.012 and 0.367 +/- 0.004, respectively, recorded at 4.5 x 10(6) cells ml-1 of Chlorella in the controls. The protective role of algae in reducing the effect of salt stress was more evident in B. calyciflorus than B. patulus.     

Effect of three food types on the population growth of Brachionus calyciflorus and Brachionus patulus (Rotifera: Brachionidae).

We compared the population growth of B. calyciflorus and B. patulus using the green alga Chlorella vulgaris, baker's yeast Saccharomyces cerevisiae or their mixture in equal proportions as food. Food was offered once every 24 h in two concentrations (low: 1 x 10(6) and high: 3 x 10(6) cells ml-1) separately for each species. The experiments were terminated after 15 days. In general, at any food type or concentration, B. patulus reached a higher population density. A diet of Chlorella alone supported a higher population growth of both rotifer species than yeast alone. B. calyciflorus and B. patulus achieved highest population densities (103 +/- 8 ind. ml-1 and 296 +/- 20 ind. ml-1, respectively) on a diet of Chlorella at 3 x 10(6) cells ml-1. When cultured using the mixture of Chlorella and yeast, the maximal population densities of B. calyciflorus were lower than those grown on Chlorella. Under similar conditions, the maximal abundance values of B. patulus were comparable in both food types. Regardless of food type and density the rate of population increase per day (r) for B. calyciflorus varied from 0.13 +/- 0.03 to 0.63 +/- 0.04. These values for B. patulus ranged from 0.19 +/- 0.01 to 0.37 +/- 0.01. The results indicated that even though Chlorella was a superior food for the tested rotifers, yeast can be effectively used at low concentrations to supplement algal requirements in rotifer culture systems.     

Comparative population growth and life table demography of the rotifer Asplanchna girodi at different prey (Brachionus calyciflorus and Brachionus havanaensis) (Rotifera) densities

Population growth and life table demography of the predatory rotifer A. girodi using spineless Brachionus calyciflorus and spined Brachionus havanaensis as prey at densities of 1, 2, 4 and 8 ind. ml^–1 at 25°C were studied. Regardless of the prey species, the population of A. girodi increased with increasing availability of Brachionus in the medium. At any given prey density, A. girodi fed B. calyciflorus showed consistently better growth than when fed B. havanaensis. The maximum population densities of A. girodi varied from 0.28 to 1.8 ind. ml^–1 depending on the prey species and the density. The rate of population increase observed in population growth studies varied from 0.17 to 0.43 day^–1 when fed B. calyciflorus and 0.09 to 0.27 day^–1 when fed B. havanaensis. Male population of A. girodi was closely related to female density. The lowest average lifespan was observed for A. girodi when fed B. havanaensis at 1 ind. ml^–1, while the converse was the case when fed B. calyciflorus at comparable prey concentration. Net reproductive rates varied from 16 to 26 offspring female^–1 lifespan^–1 depending on the prey species and concentration. Generation time of A. girodi decreased with increasing food concentrations for both the prey species. The rates of population increase obtained from life table demography were lower for A. girodi when fed B. havanaensis than when fed B. calyciflorus.     

溴氰菊酯对萼花臂尾轮虫实验种群动态的影响

采用生命表技术对暴露于不同浓度溴氰菊酯溶液中的萼花臂尾轮虫的存活和繁殖进行了研究。结果显示, 溴氰菊酯使轮虫的存活时间显著缩短, 繁殖率降低; 当溴氰菊酯浓度高达3 6 mg/L时, 轮虫的存活时间最短、繁殖率最低。与对照组相比, 除1 2 mg/L外, 其它各浓度的溴氰菊酯均使轮虫的生殖前期显著延长; 浓度为0 6和1 2 mg/L的溴氰菊酯使轮虫的生殖期显著延长, 而浓度为2 4和3 0 mg/L的溴氰菊酯却使轮虫的生殖期显著缩短; 1 2 mg/L的溴氰菊酯使轮虫的平均寿命显著延长。轮虫的生命期望、世代时间、净生殖率和种群内禀增长率均随溴氰菊酯浓度的升高而下降。当溴氰菊酯浓度升高达1 2 mg/L时, 轮虫的净生殖率开始与对照组有显著差异; 而轮虫的种群内禀增长率从溴氰菊酯浓度升高达2 4 mg/L时才开始与对照组有显著差异。在溴氰菊酯的毒性监测中, 净生殖率是比种群内禀增长率更敏感的指标。     

Acute and chronic toxicity of the pesticide methyl parathion to the rotifer Brachionus angularis (Rotifera) at different algal (Chlorella vulgaris) food densities

Methyl parathion is a commonly used insecticide in Mexico to eradicate insect pests. We evaluated the effects of this insecticide on rotifer B. angularis using both acute and chronic toxicity tests. Median lethal concentration (LC₅₀) of methyl parathion for B. angularis for a 24-h bioassay in the presence and absence of an algal diet was derived. Elevated LC₅₀ due to the survival of a greater number of test individuals in the presence of food was observed. Regardless of the toxicant concentration, population growth curves of the animals maintained at the low food level (0.75×10⁶ cells ml^-1) had a longer lag phase than those at the high food level (1.5×10⁶ cells ml^-1). Regardless of food level, an increase in the toxicant concentration in the medium resulted in decreased population growth. The lowest peak population density (50 ind. ml^-1) was observed at the highest toxicant concentration and the lower food level. The highest population density (200 ind. ml^-1) was observed in the controls at high food level. The rates of population increase per day (r) in the controls were higher (from 0.14 to 0.37 depending on the food level). Irrespective of food level, there was a decrease in the r values with increasing pesticide concentration in the medium. In order to detect the effect of population density on the growth rates in relation to the toxicant stress, we plotted the daily growth rate against initial density for the entire duration of the experiment. We observed the existence of a significantly inverse relation at all treatments except at the low food level and high toxicant concentrations (0.625 and 1.25 mg l^-1). We discuss the role of algae in the toxicity of methyl parathion to zooplankton.     

镜湖萼花臂尾轮虫种群内不同基因型克隆的生活史特征

应用生命表统计学等方法,比较了15、20、25和30℃4个温度下镜湖萼花臂尾轮虫种群内13个不同基因型克隆的生命表统计学参数和后代混交雌体百分率等生活史特征．结果表明：轮虫的世代时间、平均寿命、出生时的生命期望值、内禀增长率、净生殖率和后代混交雌体百分率对升高温度的反应均因克隆的不同而存在差异;温度、克隆及两者间的交互作用对其也都具有极显著影响．表明水环境在温度等方面所具有的时间异质性可能是镜湖萼花臂尾轮虫种群丰富的遗传变异得以维持的原因之一;自然选择出现在共存的克隆中,但其强度较低或作用时间较短是克隆共存的重要原因;遗传漂变可能在种群的基因型频率变化中起重要作用．不同基因型轮虫克隆的存在对其种群在水环境中的持续存在具有重要意义．     

邻苯二甲酸酯类物质对萼花臂尾轮虫种群增长和有性生殖的影响

以萼花臂尾轮虫(Brachionus calyciflourus)为受试动物,以17β-雌二醇(E2)为阳性对照,运用3d种群增长和4d休眠卵产量实验方法研究了不同浓度的邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二异辛酯(DEHP)和邻苯二甲酸丁苄酯(BBP)对轮虫种群增长和有性生殖的影响。结果显示,与空白对照组相比,0.05-5000μg/L的E2和500μg/L的BBP显著提高了轮虫种群增长率,而0.5和5000μg/L的DBP以及0.05和0.5μg/L的BBP使轮虫种群增长率显著降低;0.5-500μg/L的E2、50和500μg/L的DBP、0.005和500μg/L的DEHP和500μg/L的BBP显著提高了轮虫的休眠卵产量,而5000μg/L的DBP和0.05μg/L的BBP却与其相反;5和500μg/L的E2、50和500μg/L的DEHP以及500μg/L的DBP和BBP均使轮虫混交率显著上升,而0.005和0.05μg/L的E2、5000μg/L的DBP和DEHP及0.5μg/L的BBP显著降低了轮虫种群中混交雌体受精率;除5000μg/L的E2显著降低轮虫种群中的混交雌体数/非混交雌体数之外,其它所有处理组均对其无显著性影响;5、500和5000μg/L的E2、5000μg/L的DBP和5-5000μg/L的DEHP均使轮虫种群中的带卵雌体数/不带卵雌体数显著升高,而BBP对其无显著影响。在实验设置浓度范围内,轮虫种群中的混交雌体数/非混交雌体数与E2浓度间、轮虫种群中的混交雌体受精率和种群增长率与DBP浓度间、轮虫休眠卵产量与DEHP浓度间、轮虫混交率与BBP浓度间均具有显著的效应-剂量关系     

镜湖萼花臂尾轮虫夏季种群内不同克隆的生活史特征

应用生命表统计学等方法对镜湖萼花臂尾轮虫夏季种群内4个在生化遗传特征上互不相同的克隆（克隆A、B、c和D）在4种温度（15℃、20℃、25℃和30℃）下的生活史特征及其对升高的温度的反应进行了比较研究。结果表明,温度对萼花臂尾轮虫存活率和繁殖率的影响在不同克隆间存在着差异。20℃和25℃下,4个克隆轮虫的世代时间和净生殖率均分别无显著的差异;20℃、25℃和30℃下,4个克隆轮虫的平均寿命和出生时的生命期望亦然。其余各温度下,4个克隆间轮虫的其他生命表参数均有显著的差异。20℃、25℃和30℃下,4个克隆轮虫所产后代中的混交雌体百分率间均具有显著的差异,且克隆c轮虫所产后代中的混交雌体百分率最高。15℃下,克隆D轮虫的个体适合度最高;25℃下,克隆A和B轮虫的个体适合度较高。4个克隆轮虫的生活史特征对升高的温度的反应也存在着差异。忽略温度的影响时,4克隆间,克隆D轮虫的世代时间、平均寿命和出生时的生命期望最短,净生殖率、种群内禀增长率和个体适合度均最低;克隆C轮虫所产后代中的混交雌体百分率最高。30℃下,4个克隆轮虫的种群内禀增长率存在着差异可能是不同基因型的轮虫克隆群在种群内所占的比例不同的重要原因;而它们的个体适合度相似则可能是不同基因型的轮虫克隆群在夏季镜湖中共存的主要原因之一。     

Life table demography and population growth of Brachionus variabilis Hempel, 1896 in relation to Chlorella vulgaris densities

We studied the life history variables and population growth characteristics of Brachionus variabilis, which was recorded for the first time from Mexico. The animals were fed Chlorella, using five concentrations (0.25, 0.5, 1, 2 and 4 × 10⁶ cells ml^–1) at 25 °C. Food density was observed to have significant effect on life expectancy, average lifespan, gross reproductive rate, net reproductive rate, generation time and population growth rate. The average lifespan ranged from 3 to 6 days depending on the food density. The net reproductive rate ranged from 2 to 7 neonates female^–1 d^–1. The rate of population increase per day varied from 0.14 to 0.35. The highest net reproductive rate and average lifespan and life expectancy were recorded at Chlorella concentrations of 1 × 10⁶ and 2 × 10⁶ cells ml^–1.     

在培养基和食料中添加铅和镉对轮虫种群动态的影响

由于工业活动的影响,墨西哥水体环境中的重金属浓度在上升.浮游动物,尤其是轮虫类,由于对环境变化十分敏感而且是淡水中的常见组成部分,因此被广泛用于生态毒理试验以确定水质标准.在不同的胁迫途径下(如通过培养基或食料),重金属的毒性是不同的.在本研究中,通过在轮虫Brachionus rubens的培养基和食料中添加重金属这两种途径,我们评估了镉和铅的效应.对于这两种重金属,均采用将轮虫置于含0.5×106个/ml绿藻的培养基中或每天喂食经5倍于LC50值的金属处理(1,2和4h)的绿藻.对于在培养基中添加镉,使用了三个毒性水平(0.1,0.2和0.4 mg/L),铅的浓度分别为0.005,0.010 和0.015 mg/L.基于LC50的数据,B.rubens对铅的敏感性要比镉高24倍.镉浓度为0.4 mg/L时,培养基中加入镉造成B.rubens的生长趋缓.而喂食经不同时间处理的绿藻后,轮虫的密度随着食料在重金属中处理时间的延长而减小.培养基中或食料中添加铅时,轮虫种群生长的的趋势与在镉处理下的情况类似.随着培养基中重金属浓度的增加,每天种群增长率(r值)会减小.在培养基和食料处理两种不同途径下,r值会在0.33(对照)到0.02 d-1(经重金属处理)间变化[动物学报 51(1)46-52,2005].     

镜湖萼花臂尾轮虫夏季种群等位酶分析以及克隆间的生殖差异

应用聚丙烯酰胺凝胶垂直板电泳技术和特异性染色方法,对采自芜湖市镜湖的萼花臂尾轮虫(Brachionuscalyciflorus)夏季种群内的16个克隆进行了等位酶分析。在检测的6种等位酶系统中,依据葡萄糖磷酸异构酶(GPI)和苹果酸脱氢酶(MDH)的酶谱在克隆间所存在的明显差异,将镜湖萼花臂尾轮虫夏季种群内的16个克隆划分为4个互不相同的克隆群。对由4个克隆群中分别随机选取的1个克隆(共4个克隆,分别命名为克隆A、克隆B、克隆C和克隆D)在4种斜生栅藻(Scenedesmusobliquus)密度(1.0,2.0,4.0和8.0×106cells/ml)下的孤雌生殖和有性生殖所作的研究发现,食物密度、克隆以及两者间的交互作用对轮虫的种群瞬时增长率、种群中的混交雌体百分率、混交雌体受精率和休眠卵产量等4项指标均有显著影响。4克隆中,克隆D的这4项指标均最高,而克隆B的种群瞬时增长率以及克隆A的其他3项指标均最低。克隆B的种群瞬时增长率、种群中的混交雌体百分率和混交雌体受精率均与食物密度间无显著的相关性;克隆A和C的种群瞬时增长率与食物密度间呈曲线相关,而其种群中的混交雌体百分率和混交雌体受精率均与食物密度间无显著的相关性;克隆D的种群瞬时增长率、种群中的混交雌体百分率和混交雌体受精率均与食物密度间呈曲线相关。这些结果表明:镜湖萼花臂尾轮虫夏季种群内存在“克隆共存”现象,且有些克隆间在生化遗传和生态特征方面具有明显的差异     

Effect of salinity on competition between the rotifers Brachionus rotundiformis Tschugunoff and Hexarthra jenkinae (De Beauchamp) (Rotifera)

We studied the effect of different concentrations (0, 3, 6, 9 and 12 g l^–1) of sodium chloride at one food level of Chlorella (1×10⁶ cells ml^–1) on competition between the rotifers B. rotundiformis and H. jenkinae, both of which were isolated from a saline lake. The population growth experiments were conducted for 3 weeks. Both the rotifer species did not survive beyond one week at a salinity of 0 g l^–1. Regardless of salt concentration and the presence of a competitor, H. jenkinae reached higher densities than B. rotundiformis. When grown alone, both B. rotundiformis and H. jenkinae showed optimal peak population densities at the salinity of 6 and 9 g l^–1. Since biomass wise, B. rotundiformis was larger than H. jenkinae, it showed a lower numerical abundance. Thus, the maximum peak population densities of B. rotundiformis and H. jenkinae recorded in this study were 107±3 and 203±28 ind. ml^–1. The maximal rates of population increase for B. rotundiformis and H, jenkinae when grown alone were 0.264±0.003 and 0.274±0.004, respectively. Our results also indicated that B. rotundiformis and H. jenkinae coexisted better at a salinity of 6 and 9 g l^–1 of sodium chloride while a salinity of 3 g l^–1 favoured Hexarthra over B. rotundiformis. At 12 g l^–1, both the rotifer species grown alone or together showed lower growth rates compared to those at lower salinity levels. Except 0 g l^–1, in all other salinity treatments, H. jenkinae was a superior competitor to B. rotundiformis.     

Population responses and fatty acid profiles of Brachionus calyciflorus (Rotifera) in relation to different thermal regimes

Diurnal temperature fluctuations affect ectothermic species more than endothermic taxa. We tested the effect of three fixed temperatures (20, 25 and 30 °C) and a 24 h variable (20–30 °C) on the population growth and fatty acid profiles of the common rotifer Brachionus calyciflorus. Depending on the temperature treatment, the peak population abundances of B. calyciflorus varied from 65 to 80 ind./ml, the lowest being on variable temperature range. The rate of population increase varied from 0.31 to 0.52 per day, highest being at 30 °C. There was a curvilinear relationship between the population density and the egg ratio (number of eggs/female) in all the tested temperature regimes. The egg ratio was higher (>0.6) for treatments involving fixed temperatures, but for variable temperature regime, the egg ratios were lower (<0.5). Temperature also induced changes in the fatty acid content of B. calyciflorus. While the total saturated fatty acids increased, both mono-unsaturated and poly-unsaturated fatty acids decreased with increasing temperature regime. These results have been interpreted in relation to the role of temperature (both intensity and mode of exposure) on the population growth characteristics of rotifers.     

萼花臂尾轮虫培养滤液对铜绿微囊藻、斜生栅藻和小球藻群体形成及生长的影响

为探索浮游动物和藻类之间可能存在的信息传递,研究了萼花臂尾轮虫培养滤液对铜绿微囊藻、斜生栅藻和小球藻的生长及群体形成的影响.把萼花臂尾轮虫按1000个·L^-1的初始密度置于小球藻中培养24h后,用孔径0.15μm的微孔滤膜抽滤,得到轮虫培养滤液,此滤液中含有轮虫在生活过程中释放的一些信息化学物质.将轮虫培养滤液以20%的比例分别加入纯培养的铜绿微囊藻、斜生栅藻和小球藻中,进行为期7d的试验.结果表明,萼花臂尾轮虫培养滤液能显著地促进斜生栅藻的群体形成,而对铜绿微囊藻和小球藻在群体形成方面没有显著作用.另外,该滤液能显著提高小球藻种群的增长,对铜绿微囊藻和斜生栅藻的生长无明显影响.3种藻类对萼花臂尾轮虫的潜在牧食采取了不同的生态策略:斜生栅藻形成群体,增大摄食阻力,从而降低被摄食的风险;小球藻通过提高增长率来抵消被取食的损失;铜绿微囊藻是通过其它方式来降低被牧食(例如毒素).这些方式分别是这些藻类维持种群规模的反牧食防御策略之一.     

Life history characteristics of three types of females in Brachionus calyciflorus Pallas (Rotifera) fed different algae

This study describes the life history characteristics of amictic, unfertilized mictic and fertilized mictic females of the rotifer Brachionus calyciflorus cultured individually on two different algae at 0.1 mg ml^–1 food concentration and 27 °C. The duration of the juvenile period of amictic females was significantly shorter on Chlorella pyrenoidosa Chick than on Scenedesmus obliquus Kütz or both algae together. The duration of the juvenile period of unfertilized mictic females was significantly longer, and the number of eggs produced by amictic females was significantly larger on Chlorella pyrenoidosa than on S. obliquus. When fed the same type of alga, the duration of the juvenile period of the fertilized mictic females was the longest among the three types of females, and the durations of the reproductive period of the amictic females and the post-reproductive period of the fertilized mictic females were longer than, or equal to those of the other two types of females, respectively. The number of eggs produced by an unfertilized mictic female was the largest among the three types of females, and that of amictic females was larger than or equal to that of fertilized mictic females, depending on the type of diet.     

几种培养方法对萼花臂尾轮虫(Brachionus calyciflorus)种群密度及其环境因子影响的比较研究

分别利用泥鳅 -藻 -轮虫和罗非鱼 -藻 -轮虫共生隔离培养的方法 ,研究萼花臂尾轮虫 ( Brachionuscalyciflorus)的种群密度和主要环境因子的变化。研究结果表明 :加入泥鳅的培养缸中 ,有 1 1 d轮虫数量超过 1 0 0 ind/ml,其中有 5d超过 2 0 0ind/ml,最高密度达 2 50 ind/ml;在罗非鱼的培养缸中 ,在整个实验过程中 ,种群密度超过 1 0 0 ind/ml以上的时间有 6d(第5～ 1 0天 ) ;单纯利用藻类培养轮虫时 ,种群密度较低 ,且维持时间较短 ,最高种群密度不足 1 0 0 ind/ml,利用藻类 -轮虫 -鱼类共存同一生态系统中 ,并使鱼类和轮虫隔离进行生态培养时 ,能提高轮虫种群密度 ,延长种群高峰期     

Isolation and purification of glutathione S-transferases from Brachionus plicatilis and B. calyciflorus (Rotifera)

1. The enzyme glutathione S-transferase (GST), a critical element in xenobiotic metabolism, was isolated from the marine rotifer Brachionus plicatilis and its freshwater congener B. calyciflorus. 2. In B. plicatilis, GST comprised 4.2% of cytosolic protein and was present as three separate isozymes with mol. wts 30,000, 31,400 and 33,700. Specific activity of crude homogenates was 56 nmol min-1 mg-1 protein, while that of affinity chromatography purified GST was 1850. 3. In B. calyciflorus, GST was present as two isozymes with mol. wts of 26,300 and 28,500, representing 1.0% of cytosolic protein. Crude GST specific activity was 1750 nmol min-1 mg-1 protein and purified was 72,400. 4. Rotifer GSTs are unusual because they are monomers whereas all other animals thus far investigated posses dimeric GSTs.     

Morphometric and demographic responses of brachionid prey (Brachionus calyciflorus Pallas and Plationus macracanthus (Daday)) in the presence of different densities of the predator Asplanchna brightwellii (Rotifera: Asplanchnidae)

We quantified the indirect effects of different densities (1, 4, 16 individuals per jar) of the predator Asplanchna brightwellii on the morphometry and demography of their prey Brachionus calyciflorus and Plationus macracanthus. Population growth and life table demography experiments were separately conducted for each of the two prey rotifer species while keeping A. brightwellii in indirect contact. The brachionids were fed the green alga Chlorella vulgaris at a density of 1 × 10⁶ cells ml⁻¹. As compared to those cultured in the absence of the predator, in the presence of A. brightwellii the postero-lateral spines of P. macracanthus increased by about 15 μm, while in B. calyciflorus the increase was more (>80 μm). For both the brachionid species, the peak population density significantly decreased in the presence of A. brightwellii. The reproductive variables viz., net reproductive rate, generation time, and the rate of population increase of B. calyciflorus and P. macracanthus were negatively affected in the presence of kairomones from A. brightwellii.     

Feeding preference and population growth of Asplanchna brightwelli (Rotifera) offered two non-evasive prey rotifers

Population growth rates of the predatory rotifer Asplanchna brightwelli were determined at 25 °C using a large (Brachionus calyciflorus) and a small (Anuraeopsis fissa) rotifer prey species in three concentrations (0.5, 0.1 and 2.0 g dry weight ml^-1) and in five combinations. The prey ingestion time by the predator was also measured. For B. calyciflorus the ingestion time (22.97–8.95 s) was more than six times that of A. fissa (3.68 ± 0.93). Regardless of prey type, the population growth of Asplanchna increased with increasing food density. There was a direct correlation between densities of amictic and mictic fernales. The maximum rate of population growth (1.01 ± 0.10 d^-1) was higher at high density of A. fissa prey than that at the same density of B. calyciflorus. Progressive increase of A. fissa density in the offered food combination resulted in a corresponding increase of the predator's number. Gut content analysis of A. brightwelli revealed that the number of prey ingested increased with increasing prey densities.     

Reduced investment in sex as a cost of inducible defence in Brachionus calyciflorus (Rotifera)

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