Members of the Ikaros gene family are present in early representative vertebrates

Members of the Ikaros multigene family of zinc finger proteins are expressed in a tissue-specific manner and most are critical determinants in the development of both the B and T lymphocytes as well as NK and dendritic APC lineages. A PCR amplification strategy that is based on regions of shared sequence identity in Ikaros multigene family members found in mammals and several other vertebrates has led to the recovery of cDNAs that represent the orthologues of Ikaros, Aiolos, Helios, and Eos in Raja eglanteria (clearnose skate), a cartilaginous fish that is representative of an early divergence event in the phylogenetic diversification of the vertebrates. The tissue-specific patterns of expression for at least two of the four Ikaros family members in skate resemble the patterns observed in mammals, i.e., in hematopoietic tissues. Prominent expression of Ikaros in skate also is found in the lymphoid Leydig organ and epigonal tissues, which are unique to cartilaginous fish. An Ikaros-related gene has been identified in Petromyzon marinus (sea lamprey), a jawless vertebrate species, in which neither Ig nor TCRs have been identified. In addition to establishing a high degree of evolutionary conservation of the Ikaros multigene family from cartilaginous fish through mammals, these studies define a possible link between factors that regulate the differentiation of immune-type cells in the jawed vertebrates and related factors of unknown function in jawless vertebrates.     

Continental-scale patterns of nutrient and fish effects on shallow lakes: synthesis of a pan-European mesocosm experiment

1. Results are analysed from 11 experiments in which effects of fish addition and nutrient loading on shallow lakes were studied in mesocosms. The experiments, five in 1998, six in 1999, were carried out in six lakes, distributed from Finland to southern Spain, according to a standard protocol. 2. Effects of the treatments on 29 standard chemical, phytoplankton and zooplankton variables are examined to assess the relative importance of bottom‐up (nutrient enrichment) and top‐down (fish predation) effects. For each year, the experiments in different locations are treated as replicates in a meta‐analysis. Results of individual experiments are then compared in terms of the patterns of significant influences of nutrient addition and fish predation with these overall results (the baseline), and between years in the same location. 3. The overall meta‐analysis gave consistent results across the 2 years, with nutrient loading influencing all of the chemical variables, and on average 31% of primary producer and 39% of zooplankton variables. In contrast, fish influenced none of the chemical variables, 11% of the primary producer and 44% of the zooplankton variables. Nutrient effects on the system were thus about three times greater than fish effects, although fish effects were not inconsiderable. 4. The relative importance of nutrients and fish in individual experiments often differed between years at the same location and effects deviated to varying degrees from the baseline. These deviations were treated as measures of consistency (predictability) of conclusions in repeat experiments. Consistency increased southwards and this is interpreted as a consequence of more variable annual weather northwards. 5. The influence of nutrient loading was greater southwards and this was probably manifested through naturally greater annual macrophyte abundance in warmer locations in consequence of the longer plant growing‐season. There was no trend in the relative importance of fish effects with latitude but this may partly be an artefact of the simple fish community used. These findings suggest that nutrient control should be a greater priority than biomanipulation in the restoration of eutrophicated shallow lakes in warm temperate regions. 6. Starting conditions affected the outcome of experiments. High initial concentrations of total phosphorus and planktonic chlorophyll a concentration (created by local conditions prior to the experiment) led to de‐emphasis of the importance of nutrient loading in the experiment.     

Chydorid assemblages in the sedimentary sequence of Lake La Cruz (Spain) subject to water level changes

Changes among chydorid assemblages in Lake La Cruzsediments, from a core of 178 cm length, have beenstudied using community structure indices andmultivariate methods (cluster analysis, principalcomponents analysis).The results revealed the existence of two main sourcesof variation in these assemblages. One (axis I ofPCA1) is associated with the trophic level of thelake, which is hypothetised to be greater in thebottom and upper part of the core. Both zones arecharacterised by an increase in the relative frequencyof Chydorus sphaericus, accompanied by a markedreduction in the relative frequency of the mostabundant species throughout the history of the lake,Acroperus neglectus.The other source of variation (axis II of PCA1) may beinterpreted as the alternation of periods of dryer and wetter weather. Ouranalyses show the separation of two assemblages whichalternatively prevail in the sedimentary sequence, oneconstituted by Pleuroxus laevis, Alona guttata,Graptoleberis testudinaria and, sometimes, Alonarectangula, and another dominated by Chydorussphaericus, Alona quadrangularis, Alona affinis andsometimes Leydigia species. According to theecological preferences of these species, the dominanceof the first chydorid assemblage can be related toepisodes of higher temperature and with very low andfluctuating water level, or with a high water levelbut a very reduced extent of shallow water in thelake. Prevalence of the second group corresponds toepisodes with a colder environment and permanentwaters, the level of which could be variable but insuch a way that a benthic sublittoral zone maydevelop. The structure of the community is stronglyaffected by changes in lake level. High indices offluctuation in community structure and small mean bodysize of the chydorid assemblage marked the period withmore extreme dry conditions, characterised by Alona rectangula maxima. The peaks of C. sphaericuscoincided with peaks of the index offluctuation D₀ and prevalence of smaller speciesof the chydorid assemblage.     

Protein patterns in rotifers: the timing of aging

Single rotifer individuals have been characterized biochemically to obtain a fingerprint of their physiological state using a modified ultrasensitive silver-stain procedure to detect total proteins in polyacrylamide gels. Patterns are completely uniform for young isogenic individuals raised in the same culture, but they start to change when these individuals reach a certain age. This age is close to the mean lifespan and to both the cessation of body growth and reproduction. Variability is greatest among individuals of the same chronological age, thus the rate of aging is different even among individuals having identical genotypes and experiencing the same environment.     

Salinity and temperature influence in rotifer life history characteristics

A review of temperature and salinity effects on rotifer population dynamics is presented together with original data of these effects for three clones of Brachionus plicatilis. There is a clear relationship between temperature and the intrinsic rate of increase, r: an increase of temperature — within the natural environmental range — produces an exponential increase of r, and the slope of the response depends on the genotype. The effect of salinity is also genetically dependent; the highest r for each clone is observed at the salinity close to that of its environmental origin. The response of r to temperature is mainly a consequence of the response of the individual rates of development and reproductive timing. The effect of temperature on fecundity (number of descendents per individual life time) is negligible when temperature values are within the normal habitat ranges. On the other hand, salinity seems to affect primarily fecundity. The interaction salinity-temperature may be important in clones or species living in fluctuating environments with positive response to the more frequent combinations found in the corresponding habitats.     

Indirect role of T cells in development of polioencephalitis and encephalomyelitis induced by encephalomyocarditis virus.

Infection of female BALB/c mice with encephalomyocarditis virus results in the development of a paralytic syndrome in 7 to 10 days postinoculation. Previous studies had suggested the involvement of an immune component in the development of central nervous system pathology. We have examined the effects of T-cell depletion on the development of polioencephalitis (neuronal necrosis and inflammation of the brain and brain stem) and the relative contribution of the CD4+ and CD8+ subsets following the establishment of viremia. We show that monoclonal antibody depletion of T cells is effective in the reduction of polioencephalitis when given prior to viral inoculation. However, administration of the antibodies 12 h or more after viral inoculation failed to alter the development of polioencephalitis or encephalomyelitis. We conclude that T cells are involved in the development of central nervous system disease during the initial stages of infection but are not responsible for the later progression of disease.     

Low filtering rates of <Emphasis Type="Italic">Daphnia magna</Emphasis> in a hypertrophic lake: laboratory and in situ experiments using synthetic microspheres

Zooplankton grazing was measured in Albufera of València (Spain), a shallow turbid hypertrophic lagoon dominated by filamentous bluegreens, during the period of Daphnia magna growth, to evaluate the role of this cladoceran in maintaining a clear water phase which takes place after flushing for rice cultivation practices. We found extremely low ingestion and clearance rates (CR) on latex beads in situ, using a Haney trap suggesting potentially strong inhibition of grazing by the filamentous cyanobacteria, still flourishing in the lagoon. To test the effect of filaments, we undertook laboratory feeding experiments using six different dilutions of the lagoon water to vary filament concentrations, and four different bead concentrations. A highly significant power function between CR and water dilution associated with filament concentrations was found, indicating that the ability of Daphnia to exploit smaller edible algae and thereby control phytoplankton growth would depend on filament concentration levels in the lagoon. From our results only the two more diluted treatments, 9 × 10³ and 18 × 10³ filament ml⁻¹ showed CRs not far from the range of what would be normally expected on the basis of the general relationship of feeding rate as a function of total food concentration. This means that at lower food concentrations, filaments reduce D. magna CR by increasing total food concentration beyond the incipient limiting level, as well as by moderate mechanical interference with the animal’s feeding. However, at lagoon water concentrations above 25% (corresponding to filament concentrations of 75 × 10⁵ filaments ml⁻¹), extremely low CR’s, which did not respond to any food addition, were obtained for D. magna. From these results we can infer that at concentrations beyond the above-mentioned critical level, feeding inhibition by filamentous cyanobacteria is most probably due entirely to mechanical interference. Guest editor: Piet Spaak Cladocera: Proceedings of the 7th International Symposium on Cladocera     

Relaxed circadian rhythm in zooplankton along a latitudinal gradient

To test whether aquatic invertebrates are able to adjust their diel migratory cycle to different day length and presence of predators, we performed standardized enclosure experiments in shallow lakes at four different latitudes from southern Spain, with strong night–day cycles, to Finland where daylight is almost continuous during summer. We show here that nearly continuous daylight at high latitudes causes a relaxation in diel migratory behaviour in zooplankton irrespective of predation risk. At lower latitudes, however, similar conditions lead to pronounced diel rhythms in migration. Hence, zooplankton may show local behavioural adaptations in their circadian rhythm. They are also able to make risk assessments as to whether diel migration is beneficial or not, manifested in a lack of diel migration at near constant daylight, irrespective of predator presence. Our results provide an additional explanation to previous knowledge regarding diel migrations among aquatic invertebrates by showing that both physical (light) and biological (predation) factors may affect the migratory behaviour.     

Remote sensing application for the study of rapid flushing to remediate eutrophication in shallow lagoons (Albufera of Valencia)

Albufera of Valencia shallow lagoon experiences water clarification about once a year. This study aimed to observe the timing of water clarity events and to detect the associated flow during these periods. Spatial variation in chlorophyll a along the Albufera was observed using remote sensing images. Due to the lagoon’s spatial complexity and the varying water qualities flowing in from more than 60 tributaries, remote sensing was the only approach that could obtain images simultaneously covering the entire lagoon. The data were used to explore the evolution, duration and intensity of the clear-water phase, and the lagoon’s subsequent re-eutrophication. The duration and intensity of the clear-water phase varied across the lagoon, but complete water quality renovation occurred in 1 week. Our analysis demonstrates that rapid flushing could remediate the lagoon eutrophication.