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  • 1
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Freshwater biology 35 (1996), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. This paper describes the effects of differences in food quantity and quality on selected life history traits of Ceriodaphnia pulchella. Animals were fed with four concentrations of two green algae, Scenedesmus obliquus and Chlamydomonas globosa, given separately as well as in a 1 : 1 mixture.2. In most cases growth, reproduction and condition of the animals and consequently the rate of population increase, r, increased with food concentration. Life history parameters of animals raised on S. obliquus were lowest, whereas no significant differences were found between animals fed with C. globosa and with the mixture of the two algal species.3. In contrast to the large effects of food quantity and quality found in the laboratory, an analysis of the population dynamics of C. pulchella in Lake Tjeukemeer showed that the effect of changes in food conditions during the growing season of this species was limited, although overall food levels seemed to be poor throughout the year.4. Changes in the birth rate of the population are mainly governed by changes in temperature, and possibly by changes in the densities of the invertebrate predator Leptodora kindtii.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 398 (1999), S. 382-382 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] It has long been known that the waterflea Daphnia hyalina exhibits diel vertical migration in the water column, but the chemical that triggers this behaviour has not been identified. We find that trimethylamine (TMA), which is a major component of the odour produced by decaying fish, induces ...
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 103 (1995), S. 309-318 
    ISSN: 1432-1939
    Keywords: Coexistence ; Hybrid ; Competition ; Daphnia ; Hemispecific
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract I investigated the competitive relationships between two species of Daphnia, D. galeata and D. cucullata, and their interspecific hybrid. The term hemispecific competition was introduced to describe competition between parental species and hybrids. In eutrophic Tjeukemeer both parental species were found to compete with the hybrid, whereas competition between D. galeata and D. cucullata seemed limited. Although the effect of competition on life history traits of daphnids may be profound, the influence of the competitors on the seasonal dynamics of the Daphnia species seems limited.
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  • 4
    ISSN: 1573-5117
    Keywords: microcrustacean zooplankton ; tropical limnology ; biomass ; production ; empirical relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Production, biomass and productivity of the microcrustacean zooplanktonpopulations of three low-land reservoirs, Tissawewa (eutrophic), Ridiyagama(moderately eutrophic), and Muruthawela (mesotrophic) in South-east SriLanka were studied. The temporal variation of zooplankton production wasstudied in Tissawewa on basis of fortnightly sampling on five fixed samplingstations for 2 years. Zooplankton production was relatively high, mainlybecause of high copepod production predominantly realised due to twocalanoid copepods, Phyllodiaptomus annae and Heliodiaptomus viduus. Abouthalf of the copepod production was contributed by the naupliar instarstages, whereas the contribution of the eggs was generally much smaller(〈20%). In contrast, the cladoceran production consisted for ca50–70% of egg production. The results of this study werecompared with those from more than twenty other tropical and subtropicalwaterbodies reported in the literature by deriving empirical relationshipsbetween mean phytoplankton biomass and mean zooplankton biomass andproduction. Mean zooplankton biomass and annual zooplankton production werefound to be positively related to mean phytoplankton biomass, and meanphytoplankton biomass proved to be a good predictor of mean zooplanktonbiomass (r2 = 0.58) and a moderate good predictor ofannual zooplankton production (r2 = 0.43). However,the relationships between the mean phytoplankton biomass and zooplankton P/Bwere not significant neither for small-bodied and large-bodied cladoceransnor for copepods.
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  • 5
    ISSN: 1573-5117
    Keywords: microcrustacean zooplankton ; tropical limnology ; laboratory cultures ; growth ; development rates ; temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Length growth, instar durations, fecundity and mortality rates of fivespecies of microcrustacean zooplankton from a tropical reservoir weremeasured in relation to food quantity and temperature in laboratorycultures. Three cladocerans (Ceriodaphnia cornuta, Moina micrura,Diaphanosoma excisum), one calanoid copepod (Heliodiaptomus viduus), and onecyclopoid copepod (Mesocyclops thermocyclopoides) were studied. Filteredseston (45 µm mesh) from a local pond was used for food. Two foodconcentrations were employed: (1) 10 µg chlorophyll l−1(ca 0.25 mg Cl−1), and (2) 50 µg chlorophylll−1 (ca 1.25 mg C l−1). Food levels and watertemperature (22.5, 27.5, and 32.5 °C) used, roughly covered the rangesfound in the reservoir. Although all the three growth parameters were oftenaffected to some degree by temperature and food, the quantitative responseof the species differed. Also, the species reacted differently to the threepossible interactions (i.e. food × temperature,food × instar, andtemperature × instar). This contributed to the overalldifferences in the species responses. For the cladocerans, instar durationswere always affected by temperature. The food did not affect the durationtime of the adults and that of the combined juvenile instars, the latterexcept in one case significantly. For the two copepods food level affectedthe duration times of naupliar and copepodite instars, but the effect oftemperature was only significant for H. viduus. The development timesobserved for H. viduus were extraordinary long compared with values reportedin the literature for other tropical calanoids. This suggests that foodconditions in our culture were adversely affecting its growth rates.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 360 (1997), S. 79-88 
    ISSN: 1573-5117
    Keywords: Life history ; food
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Variation in offspring size and number has beendescribed for a wide range of organisms. In this studyI investigated the relationship between resource levelof the mother and size of her offspring in thecladoceran Daphnia magna, in order to assess whetheroffspring produced at different food levels areoptimal in size for these food levels. Optimaloffspring size was defined as the size of offspringthat yields the highest parental fitness (i.e.offspring of optimal size have the highest juvenilefitness per unit maternal effort invested in them). Iobserved that especially at the higher food levels,daphnids produced offspring that are larger than thecomputed optimal offspring size at these food levels.I interpret this as a mechanism to avoid starvation ofneonates in the case of suddenly deteriorating foodconditions.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 307 (1995), S. 109-115 
    ISSN: 1573-5117
    Keywords: Daphnia ; food quality ; life history ; standard carbon content
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this paper we describe the life history consequences of feeding Daphnia galeata with different food types in different concentrations. We fed the animals with four concentrations of two green algae Scenedesmus obliquus and Chlamydomonas globosa, given separately as well as in a 1:1 mixture. Growth, reproduction and condition of the animals and consequently the intrinsic rate of population increase, r, increased with the concentration of the food for all three experimental series. The life history parameters measured were lowest in the animals raised on C. globosa. Animals fed on S. obliquus showed higher values for r. We observed a distinct synergistic effect of the two algal species: growth, reproduction, condition and r were significantly higher for the animals raised on the mixed media as compared to the animals raised on the mono-algal media. We conclude that the two algal species represented complementary food resources.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Aquatic ecology 31 (1997), S. 89-98 
    ISSN: 1573-5125
    Keywords: fish predation ; inducible defence ; interspecific hybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We studied the combined effect of fish kairomones and food conditions on the relative tail spine length (RTL) of five Daphnia taxa, and the interaction of these factors with the vertical distribution of the daphnids. The experiment was done in two large-scale indoor containers, the so-called plankton towers in Plön, Germany. We conducted a competition experiment in which food level and the presence of fish chemicals and later fish were varied. A strong response of RTL to fish kairomones (e.g., longer tail spines), significant differences in RTL between species, but no differences in RTL with water depth were found. Further, we observed that these Daphnia taxa produced a higher RTL only under high food conditions. This suggests that there is a cost related to the production of longer tail spines. In a preliminary study in lake Plußsee, we found that Daphnia had longer average RTL than in the towers. Further, we noted significant differences in RTL between the two sampling dates, which may be related to a lower food level. We also detected a strong inverse correlation between RTL and depth. We discuss the implications of these findings for the co-existence of co-occurring Daphnia species and their hybrids.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Evolutionary ecology 11 (1997), S. 439-450 
    ISSN: 1573-8477
    Keywords: food ; life history ; predation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Variation in offspring size and number has been described for a wide range of organisms. Many theoretical models predict that in a given environment, the production of one single offspring size would yield the highest parental fitness. In most planktonic cladocerans, however, offspring size has been found to increase with size and age of the mother, and as individuals of variable size often co-occur within a population, offspring of variable sizes can be produced simultaneously. In this study, I investigated the relationship between age of the mother and size of her offspring to assess at what age of the mother the optimal offspring size was produced. Optimal offspring size was defined as that size of the offspring yielding the highest parental fitness, which translates to a definition of optimal offspring size as the one having the highest juvenile fitness per unit effort put in these juveniles. I observed that the youngest females produced offspring with the highest juvenile fitness per unit effort, and hence concluded that offspring produced by these females were of optimal size. Larger offspring produced by older females were estimated to yield only 70% of the potential fitness of optimally sized offspring.
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  • 10
    ISSN: 1573-5125
    Keywords: microcrustaceans ; Daphnia ; evolution ; interspecific hybridization ; molecular systematics ; aquatic ecology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cladoceran crustaceans are an important component of zooplankton in a wide range of freshwater habitats. Although the ecological characteristics of several cladoceran species have been well studied, biogeographical studies have been hampered by problematic taxonomic affiliations. However, recently developed molecular techniques, provide a powerful tool to subject aquatic taxa to comparative analyses. Here we highlight recent molecular approaches in aquatic ecology by presenting a simple method of DNA preparation and PCR amplification of the mitochondrial DNA (16S rDNA) in species from nine different families within the cladocera. On a broad taxonomic scale, sequence analysis of this mtDNA fragment has been used to produce the first molecular based phylogeny of the cladocera. This analysis clustered the cladoceran families in a fashion similar to that suggested by previous systematic classifications. In a more detailed analysis of the family Daphniidae, nuclear randomly amplified polymorphic DNA (RAPD), mitochondrial restriction fragment length polymorphism (RFLP) and morphological analyses were combined to identify species and interspecific hybrids within the Daphnia galeata species complex across 50 lakes in 13 European countries and one lake in Africa. The study revealed interspecific hybridization and backcrossing between some taxa (D. cucullata and D. galeata) to be widespread, and species and hybrids to frequently occur in sympatry. Genetic, as well as morphological information, suggests the occurrence of D. hyalina outside the Holarctic.
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