The Relations Between Predatory Fungus and Its Rotifer Preys as a Noteworthy Example of Intraguild Predation (IGP).

Intraguild predation (IGP) is a widespread interaction combining predation and competition. We investigated a unique IGP example among predacious fungus Zoophagus sp. and two rotifers, the predacious Cephalodella gibba and the common prey Lecane inermis. We checked the influence of the fungus on its competitor C. gibba and their joint influence on shared prey L. inermis, and the impact of the competitive predator on the growth of predacious fungus. The experiment on grown mycelium showed that Zoophagus strongly, negatively influences the growth of C. gibba (intermediate consumer) whose number did not increase throughout the experiment. The intermediate consumer was also trapped by Zoophagus and become extinct when it was its only prey, whereas in the absence of the fungus and with unlimited access to prey, its number grew quickly. As only few C. gibba were trapped by fungi when common preys were present, competition for food seems to have stronger effect on intermediate consumer population than predation. The experiment with conidia of the fungus showed that intermediate consumer significantly limits the growth of Zoophagus by reducing the number of available prey. It was observed that although the fungus can trap C. gibba, the latter does not support its growth. Trapping the intermediate consumer might serve to eliminate a competitor rather than to find a source of food. The chances of survival for L. inermis under the pressure of the two competing predators are scarce. It is the first example of IGP involving representatives of two kingdoms: Fungi and Animalia.

The potential of Lecane rotifers in microplastics removal.

Dealing with hard-to-degrade plastics pollution of terrestrial and aquatic environments is one of the most urgent problems of the modern world. The smallest fraction (<5 mm) called micro-plastics (MP) has been found everywhere from ice in Greenland, streams, rivers, soil and even in the human placenta. The goal of our research was to assess the ability of rotifers Lecane inermis to remove micro-plastics suspended in the water column. In the experiments we investigated specific interactions between MP, biofilm and rotifers specialized in feeding on biofilm. We hypothesized that MP adhere to the biofilm and after ingestion by rotifers could be extracted from the water in the form of compact conglomerates excreted with fecal pellets. In these experiments, we demonstrated that: (i) the rotifers preferentially ingest microplastics embedded in biofilm, (ii) the presence of microplastics does not affect growth and fecundity of rotifers, and (iii) that MP aggregation is significantly improved by the presence of biofilm, additionally enhanced in the presence of rotifers. Our findings will help to understand the role of micro-grazers, such as L. inermis feeding on biofilm, in the fate of MP in nature. In the longer term, our results could help to develop biotechnological tools for MP removal from the aquatic environment.

Effects of polyaluminum chloride (PAX-18) on the relationship between predatory fungi and Lecane rotifers.

PAX-18 (polyaluminum chloride) is frequently used in WWTPs (wastewater treatment plants) to overcome sludge bulking. An alternative biological method is the usage of Lecane rotifers, which can be endangered by predacious fungi. We investigated the influence of different PAX-18 concentrations on the relationship between Lecane inermis and predacious fungi (Zoophagus and Lecophagus) differing in feeding mode. High PAX concentration (6 mg Al3+ L-1) strongly limited the number of the rotifers, which in low concentration (1.2 mg Al3+ L-1), after an initial decline, increased, but significantly slower than in control. Under the simultaneous influence of Lecophagus and PAX, rotifers were driven almost extinct at the high concentration, but survived at the lower concentration and increased in the control. When treated with Zoophagus, only one or two rotifers survived in treatments and control. High concentrations of PAX significantly restricted the growth of fungi, whereas in low concentrations and control conditions, their length increased, with Zoophagus growing much quicker than Lecophagus. Zoophagus was significantly more efficient in trapping rotifers regardless of PAX concentration. The trapping ability of mycelium following extended exposure to PAX was strongly limited at high concentrations, in comparison to control. Conidia of Zoophagus turned out to be considerably more resistant to PAX-18 and starvation than Lecophagus conidia.

Rotifers weaken the efficiency of the cyanobacterium defence against ciliate grazers.

Cyanobacteria can protect themselves through limited dispersion and by increasing the compactness of the mucilage-covered cyanobacterial mat as well as by producing sheaths covering their trichomes. These features have been used in research to measure their degree of inducible defence. The influence of the presence of the rotifers Lecane inermis on the effectiveness of Phormidium sp. (Ph2) cyanobacterium defence was investigated. Experiments were conducted on the ciliates Pseudomicrothorax dubius and Furgasonia blochmanni, specialised in the ingestion of filamentous cyanobacteria. The most compact were cyanobacterial mats that were subjected exclusively to ciliates and the most dispersed were mats in the presence of rotifers alone. The presence of rotifers feeding on cyanobacterial mucilage led to the decreased effectiveness of the defence in two ways, by increasing the dispersion of cyanobacterial trichomes, thus loosening the cyanobacterial mat, and through the ingestion of the exopolysaccharide material covering the trichomes. As a result, in the presence of rotifers and the high density of ciliates, almost all the trichomes were removed. Moreover, in comparison with other treatments, a higher number of ciliates and rotifers remained active until the end of the experiments. This is the first report to show how rotifers can weaken the defence of cyanobacteria.

The discriminatory power of two biomonitors of trace metal bioavailabilities in freshwater streams.

The relative discriminatory powers of two trace metal biomonitors in European streams (the amphipod crustacean Gammarus fossarum and mayfly larvae of the genus Baetis-B. rhodani and B. vernus) are compared by discriminant function analysis using data from streams draining a zinc and lead mining area of Upper Silesia, Poland. The mayfly larvae (whether or not distinguished into the two separate species) had the better discriminatory power to distinguish between sites on the basis of local bioavailabilities of cadmium, copper, iron, lead and zinc. The bioavailabilities of the two metals lead and cadmium were the major local contributing factors to the stronger discrimination shown by the Baetis larvae.

Caddisflies Hydropsyche spp. as biomonitors of trace metal bioavailability thresholds causing disturbance in freshwater stream benthic communities.

Demonstration of an ecotoxicological effect of raised toxic metal bioavailabilities on benthic macroinvertebrate communities in contaminated freshwater streams typically requires the labour-intensive identification and quantification of such communities before the application of multivariate statistical analysis. A simpler approach is the use of accumulated trace metal concentrations in a metal-resistant biomonitor to define thresholds that indicate the presence of raised trace metal bioavailabilities causing ecotoxicological responses in populations of more metal-sensitive members of the community. We explore further the hypothesis that concentrations of toxic metals in larvae of species of the caddisfly genus Hydropsyche can be used to predict metal-driven ecotoxicological responses in more metal-sensitive mayflies, especially ephemerellid and heptageniid mayflies, in metal-contaminated rivers. Comparative investigation of two caddisflies, Hydropsyche siltalai and Hydropsyche angustipennis, from metal-contaminated rivers in Cornwall and Upper Silesia, Poland respectively, has provided preliminary evidence that this hypothesis is applicable across caddisfly species and contaminated river systems. Use of a combined toxic unit approach, relying on independent data sets, suggested that copper and probably also arsenic are the drivers of mayfly ecotoxicity in the River Hayle and the Red River in Cornwall, while cadmium, lead and zinc are the toxic agents in the Biala Przemsza River in Poland. This approach has great potential as a simple tool to detect the more subtle effects of mixed trace metal contamination in freshwater systems. An informed choice of suitable biomonitor extends the principle to different freshwater habitats over different ranges of severity of trace metal contamination.

Bioaccumulation of arsenic and silver by the caddisfly larvae Hydropsyche siltalai and H. pellucidula: a biodynamic modeling approach.

Biodynamic modeling was used to investigate the uptake and bioaccumulation of arsenic and silver from water and food by two Hydropsychid caddisfly larvae: Hydropsyche siltalai and Hydropsyche pellucidula. Radiotracer techniques determined the uptake rate constants of arsenic and silver from water, and assimilation efficiencies from food, and their subsequent loss rate constants after accumulation from either route. The uptake rate constants (±SE) of As and Ag from solution were 0.021±0.005 and 0.350±0.049Lg(-1)day(-1), respectively, for H. siltalai, and 0.435±0.054 and 0.277±0.021Lg(-1)day(-1), respectively, for H. pellucidula in moderately hard synthetic water at 10°C. The assimilation efficiencies (±SE) of As and Ag from radiolabeled ingested food were 46.0±7.7% and 75.7±3.6%, respectively, for H. siltalai, and 61.0±4.2% and 52.6±8.6%, respectively, for H. pellucidula. Ag, but not As, AEs were significantly different between species. The AE of Ag differed from the AE of As in H. siltalai, but not in H. pellucidula. Mean efflux rate constants after accumulation of metals from solution or food ranged from 0.039 to 0.190day(-1). The efflux rate constants of As and Ag accumulated from solution were significantly lower than those of As and Ag assimilated from ingested food in both species. Experimentally derived ku and ke values were then used to predict As and Ag tissue concentrations in hydropsychids collected from 13 UK sites, including metal-contaminated streams in Cornwall. Arsenic and silver concentrations in environmental water and food (suspended particles) samples were measured. Biodynamic models successfully predicted accumulated As and Ag concentrations in resident H. siltalai and H. pellucidula at each site. The models also showed that more than 95% of accumulated As and almost 100% of accumulated Ag in H. siltalai and H. pellucidula are derived from ingested food rather than from water.

Mayfly larvae (Baetis rhodani and B. vernus) as biomonitors of trace metal pollution in streams of a catchment draining a zinc and lead mining area of Upper Silesia, Poland.

Larvae of two Baetis species were used to investigate spatial and temporal variability in the bioavailabilities of cadmium, copper, lead, zinc and iron in the river Biala Przemsza and its tributaries draining an area of lead and zinc mining in Upper Silesia, Poland. Accumulated metal concentrations were measured in April, May, August and November 2000. Both species indicated significant local geographical variability in availabilities of zinc, iron, lead and cadmium, but not copper. Accumulated concentrations of lead, zinc and cadmium confirmed the high general contamination of the Biala Przemsza system by these three trace metals. Larvae showed little seasonal variation in concentrations of cadmium, copper, lead and iron. Accumulated zinc concentrations were low in Baetis rhodani in August, perhaps as a result of insufficient time for high concentrations to accumulate since hatching of the larvae. Samples collected in August most nearly matched criteria of the greatest availability of larvae for collection and their size homogeneity, minimising the possibilities of any effect of differential larval size and/or age on accumulated metal concentrations. Mayfly larvae are members of a suite of potential stream biomonitors in Central Europe, which together can provide information on the different sources of bioavailable trace metals present in aquatic ecosystems.