The seasonal dynamics of Copidodiaptomus numidicus (Gurney, 1909) and Thermocyclops dybowskii (Lande, 1890) in Castelo-do-Bode Reservoir

We investigated the population dynamics of Copidodiaptomus numidicus (Copepoda: Calanoida) and Thermocyclops dybowskii (Copepoda: Cyclopoida) in Castelo-do-Bode Reservoir (Portugal). Both species in the reservoir were regulated mainly by food availability during the summers of 1993 and 1994. C. numidicus was always more abundant than T. dybowskii in the reservoir. C. numidicus produced two generations during the sampling period of both years whereas T. dybowskii produced two and three generations in 1993 and 1994, respectively. Because of high temperatures and low rainfall in 1994, the reservoir was more eutrophic than in 1993. Higher clutch size and a higher percentage of ovigerous females suggest that both species were benefiting from better feeding conditions in 1994. Despite this, population growth was reduced in 1994 relatively to 1993. Vertebrate predation and predation by copepods seem to have been minor factors in explaining this decline. However, the presence of Mesostoma sp. in the reservoir may have contributed to the reduction of both copepod populations during specific periods in 1994 although the calanoid was more affected than the cyclopoid by this predation.     

The highly dynamic CRISPR1 system of Streptococcus agalactiae controls the diversity of its mobilome

Clustered regularly interspaced short palindromic repeats (CRISPR) confer immunity against mobile genetic elements (MGEs) in prokaryotes. Streptococcus agalactiae, a leading cause of neonatal infections contains in its genome two CRISPR/Cas systems. We show that type 1‐C CRISPR2 is present in few strains but type 2‐A CRISPR1 is ubiquitous. Comparative sequence analysis of the CRISPR1 spacer content of 351 S. agalactiae strains revealed that it is extremely diverse due to the acquisition of new spacers, spacer duplications and spacer deletions that witness the dynamics of this system. The spacer content profile mirrors the S. agalactiae population structure. Transfer of a conjugative transposon targeted by CRISPR1 selected for spacer rearrangements, suggesting that deletions and duplications pre‐exist in the population. The comparison of protospacers located within MGE or the core genome and protospacer‐associated motif‐shuffling demonstrated that the GG motif is sufficient to discriminate self and non‐self and for spacer selection and integration. Strikingly more than 40% of the 949 different CRISPR1 spacers identified target MGEs found in S. agalactiae genomes. We thus propose that the S. agalactiae type II‐A CRISPR1/Cas system modulates the cohabitation of the species with its mobilome, as such contributing to the diversity of MGEs in the population.     

Assessment of the importance of fish predation versus copepod predation on life history traits of Daphnia hyalina

Daphnia hyalina is a cladoceran present throughthe whole year except for late summer in Maranhão,a meso-eutrophic reservoir in central Portugal. Apartfrom the influence of food, both vertebrate andinvertebrate predation pressures seem to have aneffect on D. hyalina population dynamics.Enclosure experiments were designed to assess therelative importance of both types of predation. Afterthe summer crash, D. hyalina reached highernumbers in the fishless enclosures than in the lakedespite of high predation pressure upon juveniles byAcanthocyclops robustus. Fish predation upon thelargest individuals, especially large egg bearingfemales, was responsible for the lower fertility ofthe open water population when compared with theenclosure population. In the enclosures an increase intail spine length was observed. The longer tail spineprobably offered protection from copepod predation,allowing at least some of the juveniles to coexistwith their potential predator and reach the adultstage, less susceptible to copepod predation.     

Influence of drought on algal biofilms and meiofaunal assemblages of temperate reservoirs and rivers

The role of hydrological droughts in shaping meiofauna abundance through alterations in biofilm biomass and composition was investigated. In January 2005, continental Portugal was under a moderate to severe drought resulting from a 40% to 60% decrease in rainfall during the previous 12 months relative to the long-term average (1961–1990). Reservoir capacity was reduced by 30–50% relative to average values and the width of streams was reduced by 20–80% in the Zêzere River Basin (central Portugal). Algal biomass and algal class composition of biofilms was assessed through quantification of algal pigments in three reservoir and six river locations. During drought, habitat alterations are expected to be sharp in rivers while, in the absence of water quality deterioration, the habitat characteristics of reservoirs are expected to remain fairly unaffected. Chlorophylls and carotenoid pigments were extracted from biofilm samples and analysed using high performance liquid chromatography (HPLC). In the winter of 2003, during the period of average rainfall, biofilm biomass did not exceed 5 μg chlorophyll a cm⁻² at any location. River biofilm biomass was roughly half of that measured in the reservoirs. In the winter of 2005 (drought), biofilm biomass increased by more than 5-fold in river locations and remained low or decreased in the reservoirs. Algal biofilms were either dominated by Bacillariophyceae or by Chlorophyceae regardless of the existence of drought. The relative contribution of Bacillariophyceae to total biofilm biomass was higher during the drought than under average hydrological conditions. The abundance of harpacticoids, cladocerans and ostracods was favoured by the drought only in the reservoirs where an increase in diatom proportion in biofilms was observed. The increase in the abundance of cyclopoid copepods, turbellarians, nematodes and chironomids in rivers during the drought could be explained by algal class composition and biomass of biofilms and environmental variables (organic matter sediment content, phosphorus availability content and sediment granulometry). The hydrological drought appears to regulate meiofauna abundance only in river locations, possibly through the promotion of the growth of biofilms and the availability of organic matter deposited in rivers during the drought. Handling editor: D. Ryder     

New potent P-glycoprotein modulators with the cucurbitane scaffold and their synergistic interaction with doxorubicin on resistant cancer cells

The novel cucurbitacins, balsaminagenin A and B (1–2) and balsaminoside A (3) and the know cucurbitacin karavelagenin C (4), together with five new mono or diacylated derivatives (5–9) of karavelagenin C were evaluated for multidrug resistance reversing activity on human MDR1 gene transfected mouse lymphoma cells. Compounds 2–6 exhibited a strong activity compared with that of the positive control, verapamil. Structure–activity relationships are discussed. Moreover, in the checkerboard model of combination chemotherapy, the interaction between doxorubicin and compounds 2–5 synergistically enhanced the effect of the anticancer drug. Compounds 1–4 were isolated from the aerial parts of Momordica balsamina L. The structures of the compounds were established on the basis of spectroscopic methods including 2D NMR experiments (COSY, HMQC, HMBC and NOESY).     

Environmental factors determining the structure of rotifer communities in a river-shed reservoir

This study was designed to find out which environmental factors (temperature, oxygen concentration and food resources) are more important in steering the rotifers vertical distribution and community structure in an oligo-changing to-mesotrophic reservoir. It was observed that, despite the influence of temperature and oxygen content of the water, biotic factors especially the food availability and changes in trophic state were crucial in shaping the vertical distribution and species composition of rotifers in Meimoa Reservoir, located in Tagus River in Portugal.     

Zooplankton assemblages in two reservoirs: one subjected to accentuated water level fluctuations,the other with more stable water levels

The abundance, composition and dynamics of zooplankton were followed in two reservoirs of the River Douro catchment. The Serra Serrada Reservoir is subject to marked fluctuations in water levels. The highest values of total phosphorus, soluble reactive phosphorus, nitrate, water colour and chlorophyll a were found during the minimum level phase. Rotifera was dominant except in late summer and autumn when the cladoceran Ceriodaphnia quadrangula or the copepod Tropocyclops prasinus replaced them as the dominant zooplankton. Among the rotifers the most common taxa were Keratella cochlearis, Conochilus sp. and Asplanchna priodonta. Maximum rotifer density was about 80,000 ind m⁻³ in 2000, 200,000 ind m⁻³ in 2001 and 100,000 ind m⁻³ in 2002. Among the crustacean zooplankton C. quadrangula achieved densities of up to 45,000 ind m⁻³ and T. prasinus, up to 80,000 ind m⁻³. Canonical correspondence analysis revealed a strong contribution of the variation in the stored water volume, temperature, total phosphorus, chlorophyll, nitrates, and water transparency to the observed, significant association between zooplankton assemblage and environmental variables. In the Azibo Reservoir, fluctuations in water level are smaller. Only total phosphorus, cholorophyll and conductivity varied seasonally. Cladocera and Copepoda were dominant during the whole study period. The most abundant taxa were Ceriodaphnia pulchella, Daphnia longispina, Diaphanosoma brachyurum, Bosmina longirostris and Copidodiaptomus numidicus. Cladocera achieved densities of up to 25,000 ind m⁻³ and Copepoda up to 15,000 ind m⁻³. Rotifera in general reached densities of up to 6,000 ind m⁻³. On the basis of canonical correspondence analysis only temperature and conductivity were significantly associated with zooplankton assemblage.