Comparison between the gut bacterial community of laboratory cultured and wild Daphnia

The fitness of an organism is often impacted by the composition and biological activity of its associated bacterial community. Many factors, including host genetics, diet, and temperature can influence the bacterial community composition. Furthermore, these factors can differ strongly between natural and laboratory environments. Consequently, several studies have highlighted results from laboratory experiments investigating host-associated bacterial communities to be conflicting with those obtained under field conditions. Here, we compared the Daphnia magna gut bacterial communities in natural host populations with those of laboratory cultured hosts. We further analyzed changes in the gut bacterial communities after transferring hosts from natural populations to the laboratory on the short- and long-term. Results show that, in general, the gut bacterial communities from natural populations differ from those of laboratory cultures and that their composition and diversity changed one hour after being transferred to the laboratory. Over the following 14 days, the composition and diversity changed gradually. On the longer term (after two years of rearing hosts in the laboratory) the composition and diversity of the gut bacterial communities was strongly altered compared to the initial state. Our findings indicate that the gut bacterial communities of Daphnia magna in laboratory experiments is not representative for natural field conditions, and that caution should be taken when interpreting results from laboratory experiments for natural settings.

Evaluation of the Ecotoxicity of New Polyurethane Composites on Target Organisms for Aquatic and Atmospheric Environments

The present study investigated if new biocomposite materials, polyurethanes (PURs) added with functionalized cellulose fibers, produce potential toxic effects on two target organisms currently used in biomonitoring the quality of two different environmental compartments. Natural fibers were extracted from the species Spartium junceum L., a shrub commonly found in the southern region of the Mediterranean having a high cellulose content. All PURs produced were characterized by Fourier-transform infrared spectroscopy, and their structure was analyzed by scanning electron microscopy. We measured the effects of exposure to aromatic and aliphatic PUR composites (containing or not cellulose fibers) on the aquatic model organism Daphnia magna Straus, a freshwater crustacean (Cladocera), and a biomonitor of air quality, the fruticose epiphytic lichen Pseudevernia furfuracea (L.) Zopf. Leachates from aliphatic PUR composite not containing cellulose are more toxic to D. magna than all others, showing a slight acute toxicity in the case of the shortest exposure (24 h) and a moderate acute toxicity in the longer one (48 h). This effect is most likely due to the presence of free organic ammines and amides, which, in their turn, are immobilized in composites containing cellulosic fibers because of the considerable amount of chemical functional groups. Regarding lichens, both types of aliphatic PURs resulted in a toxic effect. Formulate not added with cellulose strongly promoted fungal peroxidation, whereas that which was functionalized affected the pigment concentration of the algal partner. Our results suggest that the use of cellulose in PUR production, in general, can limit the ecotoxicological effects on both test organisms and reduce the potential environmental impact due to this type of polymer. Environ Toxicol Chem 2023;42:421-436. © 2022 SETAC.

Maternal Responses and Adaptive Changes to Environmental Stress via Chronic Nanomaterial Exposure: Differences in Inter and Transgenerational Interclonal Broods of Daphnia magna

There is increasing recognition that environmental nano-biological interactions in model species, and the resulting effects on progeny, are of paramount importance for nanomaterial (NM) risk assessment. In this work, Daphnia magna F0 mothers were exposed to a range of silver and titanium dioxide NMs. The key biological life history traits (survival, growth and reproduction) of the F1 intergenerations, at the first (F1B1), third (F1B3) and fifth (F1B5) broods, were investigated. Furthermore, the F1 germlines of each of the three broods were investigated over 3 more generations (up to 25 days each) in continuous or removed-from NM exposure, to identify how the length of maternal exposure affects the resulting clonal broods. Our results show how daphnids respond to NM-induced stress, and how the maternal effects show trade-offs between growth, reproduction and survivorship. The F1B1 (and following germline) had the shortest F0 maternal exposure times to the NMs, and thus were the most sensitive showing reduced size and reproductive output. The F1B3 generation had a sub-chronic maternal exposure, whereas the F1B5 generation suffered chronic maternal exposure where (in most cases) the most compensatory adaptive effects were displayed in response to the prolonged NM exposure, including enhanced neonate output and reduced gene expression. Transgenerational responses of multiple germlines showed a direct link with maternal exposure time to 'sub-lethal' effect concentrations of NMs (identified from standard OECDs acute toxicity tests which chronically presented as lethal) including increased survival and production of males in the F1B3 and G1B5 germlines. This information may help to fine-tune environmental risk assessments of NMs and prediction of their impacts on environmental ecology.

Benefits of host genetic diversity for resistance to infection depend on parasite diversity

Host populations with high genetic diversity are predicted to have lower levels of infection prevalence. This theory assumes that host genetic diversity results in variation in susceptibility and that parasites exhibit variation in infectivity. Empirical studies on the effects of host heterogeneity typically neglect the role of parasite diversity. We conducted three laboratory experiments designed to test if genetic variation in Daphnia magna populations and genetic variation in its parasites together influence the course of parasite spread after introduction. We found that a natural D. magna population exhibited variation in susceptibility to infection by three parasite species and had strong host clone-parasite species interactions. There was no effect of host heterogeneity in experimental host populations (polycultures and monocultures) separately exposed to single strains of three parasite species. When we manipulated the genetic diversity of a single parasite species and exposed them to host monocultures and polycultures, we found that parasite prevalence increased with the number of parasite strains. Host monocultures exposed to several parasite strains had higher mean parasite prevalence and higher variance than polycultures. These results indicate that effect of host genetic diversity on the spread of infection depends on the level of genetic diversity in the parasite population.

Toxicity of single and mixed contaminants in seawater measured with acute toxicity bioassays

Different types of organic pollutants commonly detected in seawater have been evaluated by acute toxicity bioassays. Vibrio fischeri, Daphnia magna, and Selenastrum capricornotum were selected to test toxic effects of individual compounds and mixtures of these compounds, obtaining EC50 values in the range of 0.001 to 28.9 mg/l. In the case of mixtures, synergistic toxic responses were seen for a clear majority of the cases (>60%). Mixtures containing methyl-tertiary-butyl ether (MTBE) exhibit accelerated processes that result in a change in concentration required to produce a toxic effect; for example, in the case of mixtures containing MTBE and Diuron and Dichlofluanid.