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.     

The relation of biotic and abiotic interactions to eutrophication in Tjeukemeer,The Netherlands

During the summer months of 1974–1985 chlorophyll-a and total P concentration, biomass of Daphnia hyalina, smelt Osmerus eperlanus, bream Abramis brema and pikeperch Stizostedion lucioperca, water temperature and water intake from lake IJsselmeer were monitored in Tjeukemeer. During this period there were manipulations with the bream and pikeperch stocks as a consequence of the termination of a gill-net fishery in 1977, and larval smelt immigrated each year from the large lake IJsselmeer and contributed largely to the yearly smelt recruitment.The correlation matrix of the nine variables mentioned above showed a positive correlation between bream and chlorophyll-a, but surprisingly a negative one between smelt and chlorophyll-a. The latter can only be explained when smelt is the dependent variable. In a multi-linear regression there was a negative effect of temperature, chlorophyll a and pikeperch on smelt and a positive effect of water intake. Daphnia hyalina was negatively influenced by the biomass of smelt and the water intake of lake IJsselmeer. The positive relation of Daphnia hyalina and chlorophyll-a was probably related to better survival chances of D. hyalina in an Oscillatoria-rich environment when smelt is the most important predator. An increasing biomass of bream coincided with higher total-P levels and probably contributed to higher chlorophyll-a levels.     

Four different head shapes in Daphnia hyalina (Leydig) induced by the presence of larvae of Chaoborus flavicans (Meigen)

In many species of Daphnia spines, neck teeth, and enlarged or reshaped helmets are well-known as defences against invertebrate predators. Until now, Daphnia hyalina (Leydig, 1860), a common species in many European lakes, has appeared to be an exception to this rule.Here, we provide evidence that the larvae of Chaoborus flavicans (Meigen) also can induce morphological changes in D. hyalina. Specimens react morphologically to the presence of larvae in three ways: (a) by changes in the shape of head shield, (b) by the formation of spine(s) on the head, and (c) by the elongation of the tail spine. The frequency and intensity of these morphological changes are correlated positively with midge larvae densities. The most pronounced reactions occurred in young D. hyalina.The predator kairomone also induced changes in Daphnia body size.     

Zooplankton and their relationships with water quality and fisheries

Zooplankton population structure in Rutland Water changed over the first five years of the reservoir's existence. Daphnia pulex, initially dominant was replaced by D. hyalina in late 1975 and since 1979 this latter cladoceran has coexisted for part of each year with Bosmina longirostris. Population fluctuations of all the main crustacean zooplankton — D. hyalina, Cyclops spp. and Diaptomus gracilis — were erratic in the first three years (1975–1977) but have since become more regular. The relationships of the zooplankton with their potential algal food supply and with their potential predators, the fish population, are discussed.     

Contrasting migration behaviour of Daphnia pulicaria and D. galeata x hyalina, in avoidance of predation by 0+perch (Perca fluviatilis)

In spring and early summer, a small population of the large-bodied Daphnia pulicaria coexists with a much larger population of the medium-sized hybrid Daphnia galeata × hyalina in the epilimnion of Lake Maarsseveen (The Netherlands). When large shoals of juvenile perch (Perca fluviatilis) appear in the open water, both species start to migrate vertically. Since D. pulicaria has a larger body-size than D. galeata × hyalina, and is therefore competitive dominant over the hybrid, it is unlikely that both species interact via their common food resource, but they react both to fish predation. However, since they differ in size, and therefore in vulnerability for fish predation, both species adopt different strategies. The smaller bodied, and less vulnerable D. galeata × hyalina exhibits diel vertical migration ascending to the surface at dusk, and staying there during the night. In this way, benefiting from the higher temperatures of the surface layers. In contrast, the large-bodied, and more vulnerable D. pulicaria selects the deep cold hypolimnion water layers as refuge against fish predation. In this way it benefits from a safe habitat, free from fish predators, but on the other hand suffers from low water temperatures, which decrease its fitness. It is likely that the relatively higher temperature in the upper water layers serves as a proximate factor for the downward migration of D. pulicaria.     

A test of a model for planktivorous filter feeding by bream Abramis brama

Synopsis The planktivorous feeding of bream, Abramis brama on Daphnia hyalina and Bosmina coregoni was analyzed in a stepwise regression analysis with the average size (and standard deviation) of consumed organisms as dependent variable and the size of the fish, the average size (and standard deviation) of the organisms and their density in the environment as independent variables. Three basic predictions on filter feeding were formulated and tested. It was predicted that the (average) prey size should increase with fish size, but that the standard deviation should decline. Secondly the prey size should be strongly correlated with the prey size available and thirdly the prey density should have little effect on the size selection. These hypotheses could not be rejected for bream>10 cm feeding on B. coregoni and for bream>20 cm feeding on D. hyalina. The hypotheses were not valid for smaller bream as these acted as particulate or combined filter- and particulate feeders.     

Population dynamics and production of Daphnia hyalina Leydig and Daphnia cucullata Sars in Tjeukemeer

As part of a research programme on the food chains in Tjeukemeer, the Daphnia hyalina and Daphnia cucullata populations were studied for three successive years. To analyse the factors regulating the production of these two species, their population parameters (density, size distribution, fecundity) and population dynamics (birth rate, mortality rate) were studied and related to environmental factors. Since Daphnia in Tjeukemeer shows continuous recruitment, the population dynamics model INSTAR was developed and used to integrate field data with laboratory data on development rates and length-weight relationships. The dynamics of the Daphnia species are mainly regulated by temperature and fish predation, the latter affects both birth rate and mortality. Total annual Daphnia production was 3.1–6.9 g org. dry wt M^–2, and annual P/B ratio ranged from 25 to 40 for D. cucullata and from 45 to 49 for D. hyalina.     

Results Regarding the Food of the Planktic Crustaceans Daphnia hyalina and Eudiaptomus gracilis

The graph of maximum filtering and grazing rates versus particle size shows that Daphnia hyalina is a microfiltrator and Eudiaptomus gracilis is a macrofiltrator. In contrast to Eudiaptomus gracilis, Daphnia hyalina is also able to utilize larger bacteria (c. 1 μm³) as a food source.     

Effects of crowding and different food levels on growth and reproductive investment of Daphnia

The effects of daphniid crowding on juvenile growth rate, length at first reproduction, clutch size and egg size of four species of Daphnia were compared with the effects of food level. Juvenile Daphnia were grown to primipary in a flow-through system in water conditioned by different densities of the same, or another, species. At high ambient food levels, water from Daphnia that had been crowded at densities 150 l^–1 depressed growth rate and lowered body size and clutch size of D. hyalina and D. galeata; effects on the same traits of D. magna and D. pulicaria were variable (stimulation, depression, or no effect). D. hyalina and D. galeata responded to gradients of increasing daphniid density (0–300 l^–1) by altering egg mass, somatic mass and clutch size to maintain a relatively constant reproductive investment; egg mass increased with crowding and then decreased in a pattern consistent with Glazier's (1992) hypothetical model of changes in offspring size in relation to food quantity and maternal demand. Effects of crowding by conspecifics were indistinguishable from those of other species. This study, which uncouples the effect of crowding per se from ambient resource depletion, shows that chemical substances released by high densities of Daphnia can cause changes in life-history traits comparable to those that occur in response to low food levels.     

中国的被孢霉种类

被孢霉属(Mortierella Coemans)是接合菌纲(Zygomycetes)、毛霉目(Mucorales)、被孢霉科(Mortierellaceae)中的一个大属,目前已知约有90种;主要存在于土壤、植物残体、动物粪便等基物中。我国过去对被孢霉的研究不多,在《中国真菌总汇》(1979)中记录了8个种。本研究从全国22个省、市、自治区采集的2000多号样品中,分离到约220个被孢霉菌株。本研究主要采用Gams (1970, 1977)的分类系统进行分类鉴定,并对该系统进行了修改。在属下分3个亚属(Micromucor, Mortierella和Gamsiella), 8个组(Actinomortierella, Alpina,Hygrophila, Mortierella, Schmuckii, Simplex, Spinosa和Stylospora),单囊霉(Haplosporangium)被承认为独立的一个属。本研究鉴定出22个种和3个变种,包括一个新种(武夷山被孢霉Mortierella wuyishanensis sp. nov.)和一个新变种(极细无色被孢霉Mortierella hyalina(Harz) W. Gams var. subtilissima var. nov.), 14个中国新纪录。这14个新纪录为:产芽胞被孢霉(Mortierella. gemmifera M. Ellis)、园圃被孢霉(M. horticola Linnem.)、矮小被孢霉(M. humilis Linnem.)、无色被孢霉(M. hyalina(Harz) W. Gams)、印度被孢霉(M. indica B.S. Mehrotra)、英杜被孢霉(M. indohii C.Y. Chien),詹金氏被孢霉(M. jenkinii (A.L. Sm.) Naumov)、可疑极小被孢霉(M. minutissima Tiegh. var. dubia Linnem.)、易变被孢霉(M. mutabilis Linnem.)、微孢被孢霉(M. parvispora Linnem.)、角胞拉曼被孢霉(M. ramanniana(Moller) Linnem. var. angulispora (Naumov) Linnem.)、网孢被孢霉(M. reticulata Tiegh.& G. Le Monn.)、多疣被孢霉(M. verrucosa Linnem.)、轮枝被孢霉(M. verticillata Linnem.)。文中讨论和评价了一些分类性状,还列出分亚属、分组、分种和变种的检索表.每个分类单元都有描述和讨论以及线条图、并列出分布地区。     

P-load,phytoplankton, zooplankton and fish stock in Loosdrecht Lake and Tjeukemeer: confounding effects of predation and food availability

The fish community in the Loosdrecht lakes is dominated by bream, pikeperch and smelt and is characteristic of shallow eutrophic lakes in The Netherlands. The biomasses of the respective fish species amount to ca. 250, 25 and 10 kg ha^–1 and correspond to those in Tjeukemeer, another lake in The Netherlands. The average size of bream, however, is much smaller in the Loosdrecht lakes as a consequence of poorer feeding conditions. The zooplankton community in the Loosdrecht lakes is predominantly composed of relatively small species such as Daphnia cucullata, Bosmina coregoni and cyclopoid copepods, whereas in Tjeukemeer, Daphnia hyalina is permanently present in relatively high densities and the other species show a larger mean length. In the Loosdrecht lakes, the absence of D. hyalina and the smaller sizes of the other zooplankton species could be the consequence of a higher predation pressure, in combination with unfavourable feeding conditions for the zooplankton including the low density of green algae and the high density of filamentous cyanobacteria. A biomanipulation experiment in Lake Breukeleveen, one of the Loosdrecht lakes, indicated that feeding conditions were too unfavourable for large zooplankton to develop in spring, when the reduced fish biomass was not yet supplemented by natural recruitment and immigration.     

Does trimethylamine induce life-history reactions in Daphnia?

Laboratory experiments were carried out to investigate life-history reactions of Daphnia to trimethylamine (TMA), a substance, which has recently been found to induce a similar phototactic reaction in Daphnia as fish kairomones. The effects of different treatments (control, fish kairomone and TMA) on the life-history traits of five clones of D. magna and one clone of D. galeata and D. hyalina, respectively, were studied. Only D. magna exhibited significant reactions to TMA and to fish kairomone. D. galeata showed no significant responses to either TMA or to fish kairomone. D. hyalina reacted to the fish treatment with two traits (size and number of eggs at maturity). The comparison of the reaction norms to TMA and fish kairomone demonstrated that the directions of some responses to both factors were similar but were different for others such as for size at maturity. TMA resulted in a larger size at maturity in D. magna, whereas fish kairomone had no significant influence on this trait. We, therefore, conclude that trimethylamine is not the primary causative chemical agent in fish induced life-history adaptations in Daphnia.     

The effects of a temperature shock on zooplankton

Summary Exposure of 4–5 day oldDaphnia hyalina to temperatures of 32° C and higher caused substantial mortality when the exposure time was an hour or more. The tolerance ofBosmina sp. to temperature shocks appears to be about that ofD. hyalina. Naupllus larvae ofCyclops sp. were much more tolerant.Survival and reproduction ofD. hyalina at high temperatures were strongly influenced by the food concentration. In a high food concentration the reproduction is at 28° C as high as at 20° C.     

Seasonal dynamics of metabolic activity of the Daphnia community in Lake Bled (Slovenia)

Seasonal changes of the community composition, oxygen consumption (R) and respiratory electron transport system (ETS)-activity of the Daphnia community living in Lake Bled (Slovenia) were studied between January and December 1998. The ETS activity of ovigerous Daphnia females at in situ temperature ranged from 3.27 l O₂ mg dw^–1 h^–1 in February to 20.91 l O₂ mg dw^–1 h^–1 in July. Respiration rates at in situ temperature varied from 4.04 l O₂ mg dw^–1h^–1 in December to 18.68 l O₂ mg dw^–1 h^–1in July. The influence of four factors (temperature, body size, fecundity, genetic differences) on the metabolism were investigated. Both ETS activity and respiration rate significantly correlated with temperature. The proportion of hybrid D. cucullata× galeata in Daphnia community correlated significantly with respiration rate at in situtemperature and ETS activity at standard temperature also. ETS activity and respiration rate showed no significant correlation with body size and the fecundity of Daphnia, whereas ETS activity in D. hyalina × galeata and D. cucullata× galeataseparately correlated with body size. ETS activity of D. hyalina × galeata also was correlated with fecundity. Hybrid D. hyalina× galeata had up to one third lower ETS activity than D. cucullata× galeata. The mean ETS/R ratio in the Daphnia community was 1.16±0.28 (N= 12). The ETS/R ratio did not correlate significantly with temperature, body size, fecundity or the proportion of D. cucullata× galeatain the Daphnia community. Laboratory experiments showed that both hybrids had similar ETS/R ratios.     

Elemental composition of two coexisting Daphnia species during the seasonal course of population development in Lake Constance

Summary In 1986 and 1987 the seasonal course of population density, life history traits and biomass composition (CHN-elemental and ash) of two coexisting Daphnia species from L. Constance (Überlinger See) were studied. The two daphnids are morphologically similar, but demonstrate different seasonal variation of behaviour (i.e. diurnal vertical migration). With the exception of nitrogen content, the mean biomass composition of adults and that of eggs were significantly different: the dry biomass of eggs (adults) contained on average 55.6 (46.1) % C, 7.9 (6.5) % H, 9.7 (9.7) % N, and 10.0 (23.8) % ash. These values were similar to those of other daphnids; it may be concluded that the average daphnid composition is not species specific, but is determined mainly by the position in the life cycle and by the nutritional state of the animal. A distinct seasonal variation in the elemental composition of the biomass of adult daphnids was observed. It related significantly to the concentration of food, as indicated by the epilimnetic chlorophyll-a concentrations and by Secchi depth. From the amplitude of seasonal variation of elemental composition and from the shape of relationships between the elemental composition of daphnids and their food, it can be concluded that in summer the non-migrating D. galeata lives under stronger food limitation than the migrating H. hyalina. In spring, there were no differences in the biomass composition of either species. In summer, the adult fcmales of D. galeata contained significantly less carbon, and hydrogen than those of D. hyalina. In most parameters of biomass (i.e. biomass composition of adults) and of life history (i.e. clutch size, mean adult weight), D. galeata displayed higher coefficients of variation. A tendency in D. galeata to have peaks of population development carlier in the season and in D. hyalina to have them towards autumn was observed. These contrasting responses of the populations development, the seasonal variability of the biomass composition seem to support the view of Geller (1986) who called D. galeata and D. hyalina exploitative and conservative strategists respectively.This research was supported by the Deutsche Forschungsge-meinschaft within the Sonderforschungsbereich Cycling of Matter in Lake Constance (SFB 248), and by scholarship to R.B. from the Deutscher Akademischer Austauschdienst (DAAD)     

A major shift in Daphnia genetic structure after the first ice‐free winter in a German reservoir

1. Climate warming may cause disruption of trophic linkages in aquatic ecosystems and lead to changes in abundance and genetic structure of zooplankton populations. We monitored the community of the Daphnia galeata‐hyalina hybrid complex in the Saidenbach Reservoir (Saxony, Germany) using allozyme electrophoresis for three consecutive years (2005–07), including one (2007) following an unusually warm winter that prevented the formation of ice cover for the first time in the history of the reservoir. 2. Genetic composition during the 2007 season differed substantially from the two preceding years that experienced the usual 3‐month ice period. Three abundance peaks in June, July and October 2007 were dominated by hybrids of Daphnia galeata x hyalina, whereas in the 2005 and 2006 seasons two peaks in June and September were dominated by Daphnia hyalina genotypes. 3. The genetic composition of the pool of diapausing eggs produced in autumn and the rate of change of genotype abundance during the following spring indicate recruitment of the D. hyalina subpopulation from ex‐ephippial animals during the spring population increase. 4. The differing potential to contribute to the overwintering animal pool or to the inoculum from diapausing eggs was confirmed by results from laboratory life‐table experiments. Daphnia galeata clones survived longer and produced parthenogenetic offspring under winter conditions, whereas D. hyalina clones showed a shorter lifespan and produced resting eggs. 5. Our results indicate a profound role of recruitment strategy in the observed shift in genetic composition. Increasing winter temperatures predicted in the context of climate change may thus favour overwintering animals, leading to an increase in the contribution of these genotypes to the population. Such microevolutionary processes may dampen possible seasonal mismatches between daphnid populations and their food or predator populations.     

Food Quality Constraints in Daphnia: Interspecific Differences in the Response to the Absence of a Long Chain Polyunsaturated Fatty Acid in the Food Source

The effect of the long chain polyunsaturated fatty acid (PUFA) eicosapentaenoic acid (EPA, 20:53) on food quality for Daphnia galeata, Daphnia hyalina and a D. galeata×hyalina hybrid was examined. Somatic growth rates of all three species were determined when growing on EPA-free Scenedesmus obliquus and on S. obliquus which had been supplemented with free EPA prior to the growth experiments. Growth rates on S. obliquus were substantially higher in D. galeata(0.45day^–1) than in D. hyalina(0.27day^–1) and D. galeata×hyalina(0.31day^–1). Supplementary EPA increased growth of D. galeata and D. hyalina, but not of the hybrid. Hence within the D. galeata/hyalina complex species differ in their ability to cope with an EPA-free diet. Analysis of fatty acids revealed that tissue concentrations of 18:33, 18:43, 20:33 and 20:43 were higher in D. galeata than in D. hyalina which indicated higher rates of assimilation and biosynthesis of PUFAs in D. galeata. This was contrasted by lower tissue concentrations of 20:53 D. galeata than in D. hyalina which suggests that 20:53 is metabolised with growth. In the D. galeata×hyalina hybrid high PUFA assimilation and biosynthesis were associated with low growth rates which explains the finding that tissue concentrations of 20:53 were highest and that growth was not constrained by the availability of 20:53.     

Are there allelopathic interactions in zooplankton? Laboratory experiments with Daphnia

Summary Daphnia hyalina and Daphnia cucullata were kept in flow-through chambers in lake water (I), water from mass cultures of D. hyalina (II) and water from mass cultures of D. cucullata (III). A good correlation between body length and clutch size of the Daphnia was found in all cases. The regression lines of the different treatments were compared with respect to different slopes and different intercepts. D. hyalina showed the same reaction to medium II and III, but a lower regression coefficient and higher intercept in medium I. In contrast D. cucullata showed the same reaction to medium I and II, but a higher regression coefficient in medium III.     

Diurnal vertical migration of Daphnia hyalina Leydig, 1860 (Crustacea: Cladocera) in Lake Bled (Slovenia) in relation to temperature and predation

Diurnal vertical migration (DVM) of Daphnia hyalina in Lake Bled was most intense during summer stratification. The extent of DVM varied with the size of the animal and its reproductive state. Migration distances were shortest in immature specimens and longest in ovigerous females. During daytime, ovigerous females stayed deeper in the water column than females without ova or immatures. The daytime temperature of water at the median depth of the ovigerous females did not exceed 10 °C, even in the warmest season. At night they migrated upward to an environment which was warmer by as much as 9 °C.Laboratory observations indicate that specimen's size and water temperature determine the velocity of passive sinking, such that morning descent of the different groups of Daphnia can be explained by passive sinking alone.Our hypothesis is that the distribution of different groups of D. hyalina in Lake Bled is influenced by two types of predators: fish (Perca fluviatilis L. and Rutilus rutilus (L.)) and larvae of Chaoborus flavicans (Meig.), the latter appearing in the epilimnion during the night. Fish predation has a key-role at the beginning of thermal stratification. Supposing that in spring the gene pool of Daphnia consists of a mix of different genotypes, distributed at different depths during the day, fish predation combined with a presence of fish chemicals favored genotypes with a lower day-depth during the spring/summer period.     

The relationship between cladoceran body size and the growth of underyearling roach (Rutilus rutilus) (L.) in two shallow lowland lakes: a mechanism for density-dependent reductions in growth

Large planktonic Cladocera are typically the most important components of the diet of underyearling roach. Selection for large species and individuals by fish can result in a shift in the species composition of the cladoceran community as well as a reduction in the mean size of the individuals of large species and in the assemblage as a whole. Laboratory experiments demonstrated that underyearlings feeding on Daphnia hyalina smaller than 1 mm in length has a significantly lower intake of prey volume per unit time than when feeding on prey greater than 1.5 mm. A decrease in the nutritional quality of zooplankton prey, brought about by increasing predation pressure is suggested as the mechanism for density-dependent reductions in the growth of underyearling roach in eutrophic water bodies.