Predation impact of Leptodora kindtii on population dynamics and morphology of Bosmina fatalis and B. longirostris in mesocosms

1. We assessed the impact of predation by the invertebrate predator Leptodora kindtii on Bosmina longirostris and B. fatalis, which show seasonal and reciprocal succession patterns in Lake Suwa, in a mesocosm experiment using 20‐L tanks with or without the predator under different food conditions. We also analysed morphological responses of the two Bosmina species to the predator in the tanks. 2. Bosmina fatalis dominated B. longirostris regardless of predator presence under high food density. However, the presence of Leptodora induced the dominance of B. fatalis more rapidly than its absence. On the contrary, no dominance of B. fatalis was observed in tanks with low food density, irrespective of the presence of the predator. Only B. fatalis showed morphological changes in response to the presence of Leptodora. 3. Mucrone length and antennule shape (angle between body and antennule and angle between antennules) showed marked responses at both high and low food densities, but antennule length responded only at high food density. Mucrone length seems to be a more effective defence against Leptodora. 4. The results suggest that B. fatalis is a superior competitor against B. longirostris and is more resistant to Leptodora predation, especially in good food conditions. The repeatedly observed seasonal succession of the two Bosmina species in the eutrophic Lake Suwa – the replacement of B. longirostris by B. fatalis following the occurrence of abundant Leptodora– seems to be caused by the selective predation of Leptodora on B. longirostris as well as the competitive ability of B. fatalis.     

Distribution patterns and predation risk of the coexisting cladocerans Bythotrephes longimanus and Leptodora kindtii in a large lake – Lake Constance

The distributions of the coexisting, planktonic, predatory cladocerans Bythotrephes longimanus and Leptodora kindtii were studied at four different stations (Langenargen-Arbon, Fischbach-Uttwil, Bregenzer Bucht and Zeller See) of a great lake, Lake Constance. The stations Langenargen-Arbon and Fischbach-Uttwil are deep (>200 m) with a high density of the coregonid fish Coregonus lavaretus, the stations Bregenzer Bucht and Zeller See are shallow (<60 m) with lower densities of coregonid fish. B. longimanus was present in the pelagic zone from mid May to November at all stations. L. kindtii generally appeared slightly later in the year than B. longimanus. Peak abundances of B. longimanus with more than 5000 ind. m^–2 (Langenargen-Arbon) appeared in late spring. During summer, when predation pressure by fish is high, abundance of B. longimanus decreased gradually. In contrast, L. kindtii displayed maximum abundances with more than 18 000 ind. m^–2 (Zeller See) in summer. During the summer months, B. longimanus lived in greater depths than L. kindtii. Differences of vertical distribution between both species were most pronounced at the deep stations (Langenargen-Arbon, Fischbach-Uttwil). Analysis of stomachs of the planktivorous fish Coregonus lavaretus showed that B. longimanus was preferred by C. lavaretus over all other prey; Ivlev's selectivity index was 0.97–0.99. Due to this high positive selection for B. longimanus by coregonids, it is surprising that the cladoceran could maintain its existence since the first recordings in 1877. Spatial refuge or indigestible resting eggs may be the underlying mechanism for this phenomenon.     

Diel vertical migration and feeding rhythm of Daphnia longispina and Bosmina corexoni in Lake Toya, Hokkaido, Japan

Diel vertical migration (DVM) and diel feeding rhythm of two cladocerans, Daphnia longispina and Bosmina coregoni were investigated at the pelagic area of Lake Toya (Hokkaido, Japan) in May, August and October 1992. Both species performed nocturnal DVM. The amplitude of DVM, however, became smaller from May to October. Such seasonal variations in DVM could not be explained by light penetration and/or water temperature. The two species had a clear feeding rhythm; they fed at night in May and October but also after sunrise in August. These feeding rhythms appeared to be related to the light-dark cycle, but were not necessarily associated with their DVM. We suggest that the diel feeding rhythm and DVM are regulated independently by light cues.     

The food preference of vendace (Coregonus albula) in South Swedish forest lakes including the predation effect on zooplankton populations

Vendace (Coregonus albula, L.) is in the southern part of its distribution area during the summer period restricted to hypolimnion. Food is dominated by Bosmina coregoni and Daphnia sp. The selectivity index is highest for large cladocerans and large copepods.The pelagic crustacean fauna in vendace lakes is dominated by small species like Bosmina coregoni, Daphnia cristata, Thermocyclops and Mesocyclops sp. and Eudiaptomus sp. During periods of maximum vendace abundance only Bosmina coregoni is left of the cladocerans, while the abundance of cyclopoid copepods increases.     

Chaoborus predation and the function of phenotypic variation in Daphnia

To investigate the role of helmet formation in defense against predation, laboratory experiments were used to analyze the effects of morphological changes in Daphnia on susceptibility to Chaoborus predation. Behavioral observations of Chaoborus preying on helmeted and non-helmeted Daphnia suggest pre-contact advantages for helmeted prey but post-contact advantages for non-helmeted prey. Helmeted Daphnia are better at evading capture by Chaoborus but may also be more easily handled by the predator. Swimming behavior of the prey, which is influenced by the presence of a tailspine, may affect Chaoborus strike distance. These results re-emphasize the potential hydromechanical importance of body shape changes in defense against predation.     

On the relationship between the Bosmina taxa coregoni and thersites (Cladocera), as indicated by subfossil remains

A succession of morphs from Bosmina coregoni f. coregoni to B. c. f. thersites, which vary in shell and antennule characters, occurred in an undated 176 cm long sediment core from the Neversdorfer See (N. Germany).     

Cereal phosphate transporters associated with the mycorrhizal pathway of phosphate uptake into roots

A very large number of plant species are capable of forming symbiotic associations with arbuscular mycorrhizal (AM) fungi. The roots of these plants are potentially capable of absorbing P from the soil solution both directly through root epidermis and root hairs, and via the AM fungal pathway that delivers P to the root cortex. A large number of phosphate (P) transporters have been identified in plants; tissue expression patterns and kinetic information supports the roles of some of these in the direct root uptake pathways. Recent work has identified additional P transporters in several unrelated species that are strongly induced, sometimes specifically, in AM roots. The primary aim of the work described in this paper was to determine how mycorrhizal colonisation by different species of AM fungi influenced the expression of members of the Pht1 gene families in the cereals Hordeum vulgare (barley), Triticum aestivum (wheat) and Zea mays (maize). RT-PCR and in-situ hybridisation, showed that the transporters HORvu;Pht1;8 (AY187023), TRIae;Pht1;myc (AJ830009) and ZEAma;Pht1;6 (AJ830010), had increased expression in roots colonised by the AM fungi Glomus intraradices,Glomus sp. WFVAM23 and Scutellospora calospora. These findings add to the increasing body of evidence indicating that plants that form AM associations with members of the Glomeromycota have evolved phosphate transporters that are either specifically or preferentially involved in scavenging phosphate from the apoplast between intracellular AM structures and root cortical cells. Operation of mycorrhiza-inducible P transporters in the AM P uptake pathway appears, at least partially, to replace uptake via different P transporters located in root epidermis and root hairs. Electronic Supplementary Material Supplementary material is available for this article at     

Somatic embryogenesis,plant regeneration and somaclonal variation in barley

In vitro culture of immature embryo and young leaf tissues was carried out with five cultivars of barley, Hordeum vulgare. Two cultivars (Albacete and Porthos) responded poorly from both types of explants, while the three others (Dissa, Golden Promise and Ingrid) produced a high frequency of embryogenic callus from these explants (25–60%). For Dissa and Ingrid, young leaf explants were slightly better than immature embryo explants for embryogenic callus induction, while immature embryo cultures of Golden Promise responded better than young leaf explants. Thus, there appears to be a significant genotype × explant interaction in the initiation of embryogenic callus in barley.Some phenotypic variants were detected among the regenerated plants of Golden Promise and Ingrid, most originating by epigenetic changes. Only in one case was the variant phenotype heritable, probably due to a mutation in the chloroplast DNA. Mitotic alteractions were not detected. Consequently, somaclonal variation did not appear to be a very frequent event in plants regenerated from 1- to 6- month-old cultures of barley.     

Morphology and defensive structures in the predator-prey interaction: an experimental study of Parabroteas sarsi (Copepoda,Calanoida) with different cladoceran prey

Parabroteas sarsi is a predaceous calanoid copepod commonly found in South Andes lakes. Feeding experiments were carried out in order to estimate the predation rates and attack patterns on different cladoceran prey. Predation rates were related with prey sizes. The smallest prey, Bosmina longirostris, was ingested up to 5 prey pred^–1 h^–1 while the largest, Daphnia middendorffiana, only at 0.12 prey pred^–1 h^–1. The functional response of P. sarsi differed when confronted with different prey although in all cases, the number of kills increased with prey density. A saturation of ingestion rates at high prey densities was only observed for B. longirostris and Ceriodaphnia dubia juveniles. Remains seldom appeared at the end of the experiments, implying that the predator consumed prey totally. Yet, in all experiments carried out with Daphnia ambigua and D. middendorffiana, remains, including soft parts, were found. Direct observations of attack and of number and types of remains showed interference of handling by tail, helmet, and size of the prey.     

Predation of freshwater jellyfish on Bosmina : the consequences for population dynamics,body size,and morphology

Invertebrate predators may cause strong changes in behaviour, life-history, and morphology of prey species. However, little is known about the influence of jellyfish on such characteristics of their prey. This study analyses the impacts of the freshwater jellyfish Craspedacusta sowerbii on life history and morphological defenses in a population of the cladoceran Bosmina longirostris . Length of mucro and antennule, size-dependent number of eggs, size at maturity, and size of juveniles, adults, and egg-carrying females were investigated during a 23 days experiment using medusae-enriched and control enclosures filled with natural plankton populations. Significant differences in parameters investigated were found not only between treatments, but also within treatments over time. Changes in Bosmina life-history parameters and morphology in controls were probably due to predation by cyclopoid copepods. The significant increase in the size of adults and egg-carrying females as well as the increase in mucro and antennule length in medusae-enriched enclosures are discussed as defense strategies against the freshwater jellyfish.     

Leptodora kindti: efficient predator and preferred prey item in Neusiedler See,Austria

In the Neusiedler See, Leptodora kindti appeared in the plankton in April/May; the growing season lasted until November. Its optimum conditions prevailed during the summer months, when densities of >500 ind. m^–3 were recorded. First, males appeared by the mid/end of August, while maximum resting egg production occurred in September. At temperatures below 10 °C the population declined.At high population levels, L. kindti caused suppression of its preferred prey item, the juveniles of Diaphanosoma mongolianum. Twenty-five to 45% of juvenile Diaphanosoma can be eliminated by Leptodora. This predation impact is a pronounced but short-term event. During the periods of high Leptodora densities, a significant relationship between Leptodora predation and the death rate of Diaphanosoma is found.The older developmental instars of L. kindti are themselves endangered by the impact of planktivorous fish (i.e. Pelecus cultratus, Alburnus alburnus), which show a preference for Leptodora larger than 6 mm. Frequently, elimination by fish corresponds with high death rates of Leptodora. During the periods when adult Leptodora occurred in numbers >50 ind. m^–3, 55% of the variance connected with its death rate can be attributed to fish predation. The success of this population of L. kindti is discussed within the framework of predator-prey interactions.     

Cyclomorphosis inDaphnia galeata mendotae: variation and stability in phenotypic cycles

Phenotypic change is studied in a cyclomorphicDaphnia galeata mendotae population known from previous studies to be clonally diverse. Morphological analyses revealed cyclical changes in both adult and juvenile helmet length and tailspine length which were: 1) strongly correlated with mean water temperature; and 2) repeated annually during the 3-year study period. Field populations exhibited high (5% to 30%) coefficients of variation (CV) for both helmet length and tailspine length; the CV also exhibited seasonal fluctuations such that it was lowest in late summer. The period of highestDaphnia helmet development coincides with peak densities of the common invertebrate predatorsChaoborus andLeptodora. The fluctuations in CV may be due to both differential phenotypic expression of the coexisting clones and invertebrate predation.     

Contaminated sediments in the Elbe estuary: Ecological and economic problems for the Port of Hamburg

The effects of food density on competition between Bosmina longirostris and Bosmina fatalis from Lake Kasumigaura were examined in the laboratory. When the animals were reared with a high concentration of Chlorella, B. fatalis, which is slightly larger than B. longirostris in body length, had larger brood sizes and a higher rate of population growth than B. longirostris. When the species were reared together at high food density, B. fatalis overcame B. longirostris. But B. longirostris won the competition at low food density.The effects of Microcystis on the competition were also examined. When the two species of Bosmina were reared in a mixture of Chlorella and Microcystis, the populations of both species hardly increased, although individual B fatalis showed slightly better individual growth and reproduction than B. longirostris. Decomposed Microcystis, however, was utilized well by both species.In Lake Kasumigaura, the decomposition of abundant Microcystis seemed to raise the food level, favouring B. fatalis over B. longirostris.     

Biomass relationship to growth and phosphate uptake ofPseudomonas fluorescens,Escherichia coli andAcinetobacter radioresistens in mixed liquor medium

The ability ofPseudomonas fluorescens, Escherichia coli andAcinetobacter radioresistenns to remove phosphate during growth was related to the initial biomass as well as to growth stages and bacterial species. Phosphate was removed by these bacteria under favourable conditions as well as under unfavourable conditions of growth. Experiments showed a relationship between a high initial cell density and phosphate uptake. More phosphate was released than removed when low initial cell densities (10²–10⁵ cells ml^–1) were used. At a high initial biomass concentration (10⁸ cells ml^–1), phosphate was removed during the lag phase and during logarthmic growth byP. fluorescens. Escherichia coli. at high initial biomass concentrations (10⁷ cells ml^–1), accumulated most of the phosphate during the first hour of the lag phase and/or during logarithmic growth and in some cases removed a small quantily of phosphate during the stationary growth phase.Acinetobacter radioresistens, at high initial cell densities (10⁶, 10⁷ cells ml^–1) removed most of phosphate during the first hour of the lag phase and some phosphate during the stationary growth phase.Pseudomonas fluorescens removed phosphate more thanA. radioresistens andE. coli with specific average ranges from 3.00–28.50 mg L^–1 compared to average ranges of 4.92–17.14 mg L^–1 forA. radioresistens and to average ranges of 0.50–8.50 mg L^–1 forE. coli.     

The feeding behaviour of Leptodora kindti and its impact on the zooplankton community of Neusiedler See (Austria)

Leptodora kindti is a very efficient invertebrate predator. Its searching mode of preying is tactile. The setae of the first thoracic limb act as mechanoreceptors, the other thoracic limbs, thorax and head together form the shape of an open basket in which after encounter the prey is pushed in by the aid of the first thoracic limbs and the furca. In Neusiedler See, small individuals of Diaphanosoma brachyurum (0.6–0.9 mm) are the preferred prey, rarely copepods are taken. The predation rate is influenced by temperature, prey density and predator size and varies between less than one and 12 prey items per predator per day. At high predator densities, Leptodora will have a substantial effect on the Diaphanosoma population of Neusiedler See.     

Relative uptake of32P by cassava,banana, elephant foot yam and groundnut in intercropping systems

Absorption of applied³²P by the treated as well as neighbouring plants in two- and three-crop intercropping systems involving cassava (Manihot esculenta Crantz), banana (Musa (AAB) Mysore), elephant foot yam (Amorphophallus campanulatus Blume) and groundnut (Arachis hypogaea L.) was studied in field trials. Radiophosphorus applied to the root zone of one of the component species in the mixed systems was found to be absorbed not only by the treated plant but also by the neighbouring plants. Banana was the most dominant species in the cassava-banana-elephant foot yam intercropping system and accumulated the major portion of the radioactivity recovered in the whole system. Cassava planted on raised mounds absorbed³²P from the root zones of elephant foot yam and banana growing in the interspaces. Absorption of³²P from cassava mounds by elephant foot yam was negligible.In cassava-groundnut intercropping system, cassava was the dominant component accumulating about 96 to 99 per cent of the total³²P recovery in the system when the radiolabel was applied to cassava and about 48 to 88 per cent when applied to the intercrops depending on whether cassava was planted on paired row-ridge, mound or flat bed. The groundnut was able to absorb only negligible quantity of³²P from cassava root zone. The absorption of³²P by treated groundnut was highest in paired-row ridge method of planting and lowest in flat bed method of planting.     

The effect of temperature and age structure on P/B for bosmina longirostris in a small impoundment

The relationships between temperature, the age structure, and daily P/B ratios for B. longirostris are examined. Temperature is the single most important factor affecting the daily P/ B, while also having an indirect influence on the age structure. The rate of change of the daily P/B with temperature is nearly identical to the rate predicted by the ‘normal’ Krogh curve.     

Availability of phosphorus in a calcareous soil treated with rock phosphate or superphosphate as affected by phosphate-dissolving fungi

A study was undertaken to isolate some fungi exhibiting phosphate-dissolution ability, and to test whether these fungi are capable of increasing the amount of available P in a calcareous soil treated with rock phosphate (RP) or with triple superphosphate (TSP) and its subsequent uptake by sorghum (Sorghum bicolor L. Moench).Penicillium sp. and twoAspergillus foetidus (Naka) isolates significantly increased the availability of P in soil treated with RP or TSP during the growing season.Penicillium sp. isolate was more effective in increasing available P in the soil treated with RP or TSP than were Aspergillus isolates. However, the dry matter and P uptake responses to inoculation with these fungi were better in the soil treated with RP than in soil treated with TSP. In the TSP treated soil, the fungi achieved their maximum P releasing capacity two weeks earlier than in soil treated with RP. Positive and significant correlation coefficients among available P, P uptake and dry matter production at different periods of the growing season were observed following inoculation. However, none of these variables were found to be significantly correlated with the fungal populations.     

Characterization of phosphonate uptake in two Phytophthora spp. and its inhibition by phosphate

The uptake of the phosphonate ion, the active breakdown product in plant tissues of the systemic anti-Oomycete compound Fosetyl-Al (aluminium tris-Oethylphosphonate), was investigated in two Phytophthora spp. of differential sensitivity. Uptake was due to the simultaneous operation of two transport systems, one of low affinity (high K _m) and one of high affinity (low K _m). The relative contribution of each transport system varied with the external concentration of phosphonate, suggesting that phosphonate was a potent regulator of both systems. Phosphate was a partial competitive inhibitor with respect to phosphonate. Phosphate competed with phosphonate for uptake with a K _i of 105 M for P. cryptogea and 68 M for P. citrophthora. Uptake was sensitive to pH, showing a maximum at pH 5.0 to 5.5. P. cryptogea was more efficient in phosphonate uptake, although it was less sensitive to inhibition by phosphonate in vitro, than P. citrophthora. This implied that the selective activity of phosphonate was not due to differential rates of uptake of this oxyanion. These results were discussed in relation to the mode of action of phosphonate towards Oomycetes.