海洋浮游桡足类滞育的研究进展

海洋桡足类在海洋生态系统中占有重要的地位,其重要的生理现象一滞育是影响其种群数量变动的重要因子。本文对海洋桡足类滞育的形式、滞育的意义、滞育卵的孵化与发育以及诱导桡足类滞育的环境因子等方面的研究进行了综述,同时还提出了今后研究的方向,以期对桡足类滞育机制的研究提供新的思路。     

盐度和低温冷藏对桡足类休眠卵萌发的影响

休眠卵是桡足类渡过不良环境的重要生存策略,是水体桡足类种群的重要潜在补充来源。通过采集珠江口南沙海域表层沉积物,研究了不同盐度和低温冷藏对桡足类休眠卵萌发的影响。结果表明:南沙沉积物中休眠卵萌发量和萌发率在盐度为20和盐度为5的实验组中最高;用50μm孔径筛绢过滤后,50μm粒径沉积物中休眠卵萌发量显著高于50μm粒径的休眠卵(P0.05);冷藏30 d后休眠卵萌发量显著高于冷藏前休眠卵萌发量(P0.05);冷藏前的休眠卵主要是静止卵和已渡过不应期的滞育卵,而冷藏后的休眠卵主要是未渡过不应期的滞育卵,表明50μm粒径沉积物中休眠卵主要以滞育卵为主。研究结果为进一步了解河口桡足类受到盐度干扰后的潜在补充机制提供了基础数据,对揭示河口桡足类种类演替规律具有重要科学意义。     

枯林湾浮游桡足类生态研究

2000年7月至2001年7月的周年调查结果表明,粤东柘林湾浮游桡足类29属57种,其中,强额拟哲水蚤Para-ca;amis crassorpstris和短角长腹剑水蚤Ootjpma brevicomis为优势种,合计占浮游桡足类总个体数的66.7%.柘林湾是一个浮游桡足类相对丰富的海湾,年均总个体数达5.4×103ind.@m-3.浮游桡足类的种类数和总个体数均表现为湾外大于湾内的平面分布格局,周年变化基本上为单峰型,高峰期位于5～10月,最低谷位于冬季1月.     

拓林湾浮游桡足类生态研究

2000年7月至2001年7月的周年调查结果表明,粤东柘林湾浮游桡足类29属57种,其中,强额拟哲水蚤Paracalanus crassirostris和短角长腹剑水蚤Oithona brevicornis为优势种,合计占浮游桡足类总个体数的66.7%.柘林湾是一个浮游桡足类相对丰富的海湾,年均总个体数达5.4×10³ind.·m^-3.浮游桡足类的种类数和总个体数均表现为湾外大于湾内的平面分布格局,周年变化基本上为单峰型,高峰期位于5~10月,最低谷位于冬季1月。     

海洋酸化对日本虎斑猛水蚤抗氧化性指标和繁殖发育的影响

本文选取海洋桡足类日本虎斑猛水蚤(Tigriopus japonicus)为模式生物,采用生化测定和实验生态学方法,研究不同酸化胁迫对桡足类体内抗氧化性指标[超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、谷胱甘肽硫转移酶(GST)和脂质过氧化(LPO)]、幼体发育时间、世代发育时间和产后代数的影响。结果表明:海水酸化可显著诱导桡足类的抗氧化性酶(SOD和CAT)的活性,而GST活性不受酸化影响,同时酸化可显著提高桡足类的LPO水平,可见该桡足类可通过SOD和CAT活性的提高来抵抗酸化胁迫引起的氧化胁迫;另外,酸化显著缩短桡足类的幼体发育时间和世代发育时间,并显著抑制其产后代数,提示酸化可以影响海洋桡足类的种群补充和动态;酸化引起该桡足类氧化胁迫的出现,继而对细胞生物大分子(如蛋白质、核酸等)造成氧化损伤,最终影响到该动物的个体水平和种群动态(如缩短发育时间和抑制繁殖力)。     

四川省的桡足类(下)

四川桡足类区系的特点由于四川的地形复杂,桡足类的种群繁多,目前已知53种,占全国已知206种的25.73%,占全国纯淡水种类的33.76%。凉山荡镖水蚤为我省特有种。53种桡足类中,以广温性种占绝对优势,其次是南方热带性种,北方寒带性种较少。这与四川地跨东洋界和古北界,全省气候比较温和有关。哲水蚤目虽是浮游性种类,但可能由于它的躯体较大,对环境、的适应性较弱,因此地域性较强。如我省特有种只在雷波马湖采得,其他地区还未发现。但也有一些分布延伸的现象,如近方蒙镖水蚤,原仅发现于西藏和新疆,海拔高度在1040—4000米,现在我省南溪县的池塘…     

重金属对海洋桡足类的影响研究进展

桡足类是海洋浮游动物种群的主要组成部分和重要的初级消费者,重金属污染对其影响可通过食物链传递到其他海洋生物甚至人类。综述了近20 a来重金属对桡足类影响的研究进展,包括重金属对桡足类的毒性和生理效应,重金属在桡足类体内蓄积及桡足类体内重金属的食物链(网)传递。并指出今后的研究重点:桡足类体内致毒重金属的存在形式,重金属食物暴露对桡足类生理生化影响机理,以及重金属对桡足类生活史的影响。     

三峡水库坝前段蓄水前后桡足类种类组成的变化

三峡水库蓄水后库区水环境发生了巨大变化,坝前茅坪至归州的西陵峡段由激流型河流生态系统演变为相对静水的水库型生态系统。桡足类是河流、湖泊、水库中重要的浮游动物类群,在水生态系统中占有重要地位,在浮游动物的研究中备受重视[1—7]。20世纪50年代三峡水库论证时也曾对其淹没区小水体的桡足类进行过调查,并对建库后的桡足类的种类组成进行了预测,但当时在未成库区干流中没有采集到桡足类[8]。作者对三峡水库蓄水前后坝前段(茅坪至归州)的桡足类进行研究,以期为三峡水库水生态系统中桡足类的演替、水环境管理、第二和第三阶段蓄水后桡…     

厦门港表层水体磷周转的生物学过程Ⅱ：桡足类对浮游植物的摄食压力

为了解桡足类在磷的生物地球化学循环中的作用,于2005年5、8、11月和2006年3月分别在厦门时间序列站（XMTS）采用肠道色素法,研究了桡足类对浮游植物的现场摄食率,同步分析了桡足类的种类组成和数量变化,进而得到桡足类群体对浮游植物的摄食率.结果表明：厦门港桡足类对浮游植物的年平均摄食率为55.53 μg·m^-3·d^-1;其中秋季最高,为108.98 μg·m^-3·d^-1,夏季最低,为7.18 μg·m^-3·d^-1.根据试验数据估算,厦门港桡足类对浮游植物现存量的摄食压力四季平均为1.81%,春、夏、秋、冬分别为3.22%、0.06%、3.52%和0.46%.     

上海淀山湖浮游桡足类群落组成与季节变动研究

本文报道了1984年2月至1985年2月上海淀山湖浮游桡足类的群落及优势种数量季节变动的调查结果．在淀山湖共获得11种浮游桡足类,隶属2目5科10属;根据各种类出现的月份,可以把这儿种桡足类划分成4种类型,终年出现型、夏秋季型、冬春季型和畏严冬型;在湖泊敞水区的浮游桡足类,年数量变动曲线有春季、夏季以及秋季三次高峰,秋季高峰比春季、夏季高峰更突出,持续时间约两个月;中华窄腹剑水蚤、汤匙华哲水蚤、广布中剑水蚤和近邻剑水蚤这4个优势种制约了桡足类群落总数量的季节消长。浮游桡足类生物量的季节变动有4次高峰,春季及秋季高峰出现时间迟于总数量高峰,其原因是数量高峰期桡足类群落中含有约80—90％的幼体,幼体成长之后方能达到生物量高峰期。本文还就影响浮游桡足类群落数量、生物量的生态因子作了初步的讨论。     

Diapause of Cyclops vicinus (Uljanin) in Lake Søbygård: Indication of a Risk-spreading Strategy

Cyclops vicinus is reported to enter summer diapause triggered by day length in order to survive food scarcity and fish predation. Development ceases and the fourth or fifth copepodid stages persist in the sediment for several weeks. In Lake Søbygård, however, a small eutrophic lake in Denmark, C. vicinus is found in the sediment as well as in the open water throughout the year. We performed laboratory experiments to elucidate the life cycle strategy of this population. In order to find the factors that induce diapause we tested the influence of food composition and light regime on the proportion of copepods entering diapause. Further we examined the diapause pattern of the offspring from diapausing and non-diapausing parents to see whether the co-occurrence of diapausing and non-diapausing copepods results from genetic differentiation within the population. In all experiments some of the copepods developed directly into adults, while others remained at the fourth or fifth copepodid stage and displayed diapause features. The proportion of copepods that developed directly into adults was influenced by food supply. Fewer individuals entered diapause when they received a mixed diet of algae and ciliates or algae, ciliates and seston compared with a pure algal diet. The response to light was different than described in literature: about 30% of the copepods entered diapause under dark conditions, and the diapause frequency was not higher when copepods had been exposed to continuous light. The offspring from diapausing parents showed no higher tendency to enter diapause than the offspring of non-diapausing parents, indicating no genetic differentiation. We conclude that diapause in C. vicinus represents a risk-spreading strategy, modified by food. The simultaneous production of diapausing and non-diapausing offspring ensures survival under harsh conditions; the influence of the food supply on the proportion of individuals entering diapause may adjust the population to the actual environmental condition. This flexible life cycle strategy might contribute to the exclusive dominance of C. vicinus in Lake Søbygård.     

Control of Diapause by Acidic pH and Ammonium Accumulation in the Hemolymph of Antarctic Copepods

Life-cycles of polar herbivorous copepods are characterised by seasonal/ontogenetic vertical migrations and diapause to survive periods of food shortage during the long winter season. However, the triggers of vertical migration and diapause are still far from being understood. In this study, we test the hypothesis that acidic pH and the accumulation of ammonium (NH₄ ⁺) in the hemolymph contribute to the control of diapause in certain Antarctic copepod species. In a recent study, it was already hypothesized that the replacement of heavy ions by ammonium is necessary for diapausing copepods to achieve neutral buoyancy at overwintering depth. The current article extends the hypothesis of ammonium-aided buoyancy by highlighting recent findings of low pH values in the hemolymph of diapausing copepods with elevated ammonium concentrations. Since ammonia (NH₃) is toxic to most organisms, a low hemolymph pH is required to maintain ammonium in the less toxic ionized form (NH₄ ⁺). Recognizing that low pH values are a relevant factor reducing metabolic rate in other marine invertebrates, the low pH values found in overwintering copepods might not only be a precondition for ammonium accumulation, but in addition, it may insure metabolic depression throughout diapause.     

Population differences in the timing of diapause: a test of hypotheses

Summary The reproductive phenology of the freshwater copepod Diaptomus sanguineus differs markedly between populations residing in two Rhode Island ponds. In a permanent pond the population switches abruptly from making subitaneous (immediately hatching) eggs to diapausing eggs at the end of March each year. In contrast, a temporary pond population switches egg types in May, returns to production of subitaneous eggs in June, and concludes the reproductive season by making diapausing eggs in July. An ESS model suggests that the pattern of diapause expected of a copepod population is a function of annual variation in the onset of harsh conditions (catastrophe date). When variation is relatively low, the superior strategy is for diapause to begin a constant period before the mean catastrophe date. When variation is high, females should make first subitaneous eggs and then diapausing eggs irrespective of the expected catastrophe date. With discrete generations, such a population would alternate between egg types. In the permanent pond, variation of catastrophe date the spring onset of planktivory by sunfish is low, whereas in the temporary pond variation of the catastrophe (pond drying) is high. The model predicts well the phenology of the two copepod populations.In the research reported here, we tested the hypothesis that copepods from the permanent pond, which switch to diapause at the same time every year, are cued by the environment to begin diapause (i.e. by photoperiod, temperature, or both), whereas those from the temporary pond make both egg types regardless of environmental conditions. In opposition to our hypothesis, experimental results indicate that diapause in both populations is cued by the environment. The distinct reproductive phenologies documented in the two populations apparently result from the copepods responding to different environmental cues, rather than one being responsive to the environment while the other is not.     

Diapause, a potent force in the evolution of freshwater crustaceans

After a brief historical review of the discovery of diapause in freshwater crustaceans, its dramatic nature in certain cyclopoid copepods, in which diapausing individuals may occur at densities of > 10⁶ per m², is used to illustrate the enormous ecological significance of the phenomenon. Some of the problems presented by dispause in cyclopoid copepods are noted, including the different behaviour in different lakes of what appears to be a single species. Different physiological cues or different genetic endowments are clearly involved.The wider incidence of diapause in freshwater copepods and ostracods is noted.Among freshwater crustaceans it it the Branchiopoda that have universally adopted diapause, always at the egg stage. Even such an ancient order as the Anostraca, perhaps the most primitive of all crustaceans, produces elaborately constructed resting eggs that are capable of cryptobiosis, can remain viable in a dry state for long periods, and can tolerate extreme conditions. The nature of branchiopod resting eggs is briefly reviewed. Of these, only those of the Anomopoda are protected by containers derived from the parental carapace. These are mechanically complex in the most advanced species but, as shown by fossils, are extremely ancient structures.Factors initiating the onset and termination of diapause in branchiopods are briefly noted, and the process of hatching of resting eggs is outlined.     

二化螟滞育幼虫的蛋白和核酸含量以及保护酶活性的变化

为了阐明二化螟Chilo supprressalis滞育幼虫的分子特征及滞育期间保护酶活性的变化规律, 本研究应用Trizol法、 总量DNA提取法和蛋白定量试剂盒, 测定了在长光周期16L∶8D和25℃下发育的非滞育老熟幼虫、 在短光周期12L∶12D 和25℃下诱导滞育51 d的幼虫（称为滞育0个月）、 滞育1, 2和3个月幼虫的核酸含量和总蛋白含量; 同时应用试剂盒测定了老熟幼虫、 滞育0, 1和2个月的二化螟幼虫5种保护酶（POD, CAT, SOD, LDH和ATP酶）的活性。结果表明： 滞育幼虫的总RNA含量显著低于非滞育的老熟幼虫（P<0.05）, 而滞育1, 2和3个月的幼虫之间没有显著差异（P≥0.05）。老熟幼虫的总DNA含量显著高于滞育幼虫（P<0.05）。老熟幼虫的RNA/DNA比值较低, 滞育幼虫的RNA/DNA比值较高, RNA/DNA比值随着滞育时间的推移呈现出先上升后下降的趋势。滞育期大于1个月的幼虫中蛋白含量均显著高于非滞育的老熟幼虫（P<0.05）, 而滞育1, 2和3个月的幼虫之间没有显著差异（P≥0.05）。二化螟幼虫体内5种保护酶活性随发育阶段不同而存在差异。滞育幼虫中POD, CAT和SOD的活性随滞育时间延长而逐渐增强, 滞育2个月幼虫中的活性最高, 而非滞育老熟幼虫中的活性最低; LDH和ATP酶的活性则相反, 非滞育老熟幼虫中的活性最高, 滞育2个月幼虫中的活性最低。这些结果说明, 总RNA和DNA含量降低、 RNA/DNA比值先升后降、 总蛋白含量升高以及保护酶活性的变化是二化螟幼虫滞育过程中的主要生理特征。     

Observations of neutral buoyancy in diapausing copepods Calanoides acutus during Antarctic winter

The herbivorous Antarctic copepod Calanoides acutus overwinters inactively in a resting stage (diapause) at depths below 500 m. It is assumed that during diapause C. acutus is neutrally buoyant in order to retain energy reserves otherwise depleted by swimming activities. However, so far, no experimental observations on its buoyancy have been reported and our knowledge of buoyancy regulation mechanisms is incomplete. In the present study, species-specific differences in buoyancy were assessed visually. Observations were made of specimens from the diapausing cohort of C. acutus and compared to another herbivorous copepod Calanus propinquus, which overwinters actively feeding in the upper water layers. Freshly caught copepods were anaesthetized in a 3-amino-benzoic acid ethyl ester (MS222) in seawater solution in order to exclude the influence of swimming movements on buoyancy control. It was shown that C. propinquus was negatively buoyant, whereas diapausing C. acutus remained neutrally buoyant. This is the first record that neutral buoyancy in diapausing copepods is maintained by the biochemical body composition without the additional need of swimming movements.     

The effect of diapause emergence on the seasonal dynamics of a zooplankton assemblage

1. The role of seasonal phenology in the emergence of zooplankton from diapause in patterns of seasonal abundance in the water column was investigated in Oneida Lake, New York. Replicate emergence traps, placed in contact with the lake sediments at two locations (one at a shallow site and one at a deep site), were monitored between May and August.
2. Although six rotifer taxa showed a clear seasonal succession in the water column throughout the study period, all but one taxon emerged exclusively in spring. Three cladoceran and three calanoid copepod species, also present in the water column throughout the study period, again showed predominantly spring emergence. In contrast, three cyclopoid copepod species had distinct seasonal periods of emergence that corresponded, at least in part, to the timing of abundance peaks in the plankton.
3. These results for a single lake are largely consistent with patterns observed or inferred by other investigators for other lakes: variable dependence of abundance in the plankton on diapause emergence for species with long-lived diapausing eggs (i.e. rotifers, cladocerans and calanoid copepods), and much closer dependence for species with short-lived diapausing immature stages (i.e. cyclopoid copepods).     

Population differences in the timing of diapause: adaptation in a spatially heterogeneous environment

Summary Populations of the planktonic copepod, Diaptomus sanguineus, live in permanent and temporary freshwater ponds in Rhode Island. All ponds in which they occur become uninhabitable at some time during the year, but the nature and timing of the harsh period varies both spatially and temporally. Females produce discrete clutches either of subitaneous eggs which hatch immediately or of diapausing eggs which hatch the following season. The two egg types show distinct chorion morphologies under transmission electron microscopy. In permanent ponds the copepods start making diapausing eggs in March, one month before rising water temperatures induce planktivorous sunfish to become active. In temporary ponds diapausing eggs are produced, in a complex pattern from May to July, before the water disappears in late summer or early fall.We investigated the spatial scale at which D. sanguineus is adapted to this complex environment. In a reciprocal transfer experiment between temporary and permanent bodies of water, female copepods placed in new ponds made subies of water, female copepods placed in new ponds made subitaneous and diapausing eggs in the same sequence as control females retained in their home ponds. The copepod populations enter diapause at times appropriate for the local habitat conditions they experience, but inappropriate for other, nearby ponds. Transplanted females were unable to sense a change in pond type or to adjust egg production accordingly. We conclude that D. sanguineus populations are adapted to the specific conditions of isolated ponds rather than to a broader geographical region containing several pond types.     

Dissolved solids do not induce diapause in the calanoid copepod Aglaodiaptomus leptopus

The effect of different total dissolved solid levels (TDS) was investigated as a predictor of diapause induction in the calanoid copepod Aglaodiaptomus leptopus. We collected adult copepods in the field and monitored seasonal changes in diapause egg production. We determined total dissolved solid levels, conductivity and temperature values from five ponds. In experimental work, females bearing clutches, collected from the field, were monitored under laboratory conditions to determine the extent of diapause induced. Females without clutches were placed with males and then subjected to low, medium and high TDS levels. After six days, females bearing clutches were isolated to determine the proportion of clutches that were diapausing. The relationship between TDS and food levels was calculated using Williamson and Butlers food limitation index (f). We concluded that neither TDS nor temperature are predictors of the induction of diapause in this study. The obtained results suggest, however, that density possibly plays a role in predicting diapause induction.     

Termination and induction of diapause in the gypsy moth larval parasitoid, Apanteles melanoscelus

Diapause in Apanteles melanoscelus can be terminated by exposure of the diapausing last instar larvae within their cocoons to 5°C for a period of 8 or more weeks. Photoperiod has no consistent influence upon diapause termination, but is of paramount importance for diapause induction. At less than 16 hr light per day virtually all larvae diapause, and at 18 hr and above very few larvae diapause. By exposing different larval stages to different photoperiods it was found that older larvae were most sensitive to the light-dark cycle. It was also noted that cocoons of diapausing larvae are larger than those of non-diapausing larvae.