New Publications

Using additive modelling to quantify the effect of chemicals on phytoplankton diversity and biomass

scitotenvEnvironmental authorities require the protection of biodiversity and other ecosystem properties such as biomass production. However, the endpoints listed in available ecotoxicological datasets generally do not contain these two ecosystem descriptors. Inferring the effects of chemicals on such descriptors from micro- or mesocosm experiments is often hampered by inherent differences in the initial biodiversity levels between experimental units or by delayed community responses. Here we introduce additive modelling to establish the effects of a chronic application of the herbicide linuron on 10 biodiversity indices and phytoplankton biomass in microcosms. We found that communities with a low (high) initial biodiversity subsequently became more (less) diverse, indicating an equilibrium biodiversity status in the communities considered here. Linuron adversely affected richness and evenness while dominance increased but no biodiversity indices were different from the control treatment at linuron concentrations below 2.4 μg/L. Richness-related indices changed at lower linuron concentrations (effects noticeable from 2.4 μg/L) than other biodiversity indices (effects noticeable from 14.4 μg/L) and, in contrast to the other indices, showed no signs of recovery following chronic exposure. Phytoplankton biomass was unaffected by linuron due to functional redundancy within the phytoplankton community. Comparing thresholds for biodiversity with conventional toxicity test results showed that standard ecological risk assessments also protect biodiversity in the case of linuron.

Full reference (link)

Viaene K, De Laender F, Van den Brink PJ, Janssen C. 2013. Using additive modelling to quantify the effect of chemicals on phytoplankton diversity and biomass Science of the Total Environment 449:71-80.

Interactive effects of a bacterial parasite and the insecticide carbaryl to life-history and physiology of two Daphnia magna clones differing in carbaryl sensitivity

aquatic toxicologyNatural and chemical stressors occur simultaneously in the aquatic environment. Their combined effects on biota are usually difficult to predict from their individual effects due to interactions between the different stressors. Several recent studies have suggested that synergistic effects of multiple stressors on organisms may be more common at high compared to low overall levels of stress. In this study, we used a three-way full factorial design to investigate whether interactive effects between a natural stressor, the bacterial parasite Pasteuria ramosa, and a chemical stressor, the insecticide carbaryl, were different between two genetically distinct clones of Daphnia magna that strongly differ in their sensitivity to carbaryl. Interactive effects on various life-history and physiological endpoints were assessed as significant deviations from the reference Independent Action (IA) model, which was implemented by testing the significance of the two-way carbaryl × parasite interaction term in two-way ANOVA's on log-transformed observational data for each clone separately. Interactive effects (and thus significant deviations from IA) were detected in both the carbaryl-sensitive clone (on survival, early reproduction and growth) and in the non-sensitive clone (on growth, electron transport activity and prophenoloxidase activity). No interactions were found for maturation rate, filtration rate, and energy reserve fractions (carbohydrate, protein, lipid). Furthermore, only antagonistic interactions were detected in the non-sensitive clone, while only synergistic interactions were observed in the carbaryl sensitive clone. Our data clearly show that there are genetically determined differences in the interactive effects following combined exposure to carbaryl and Pasteuria in D. magna.

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Interactive effects of a bacterial parasite and the insecticide carbaryl to life-history and physiology of two Daphnia magna clones differing in carbaryl sensitivity

Full reference (link)

De Coninck DIM, De Schamphelaere KAC, Jansen M, De Meester L, Janssen CR. 2013. Interactive effects of a bacterial parasite and the insecticide carbaryl to life-history and physiology of two Daphnia magna clones differing in carbaryl sensitivity. Aquatic Toxicology 130-131: 149-159.

Combined and interactive effects of global climate change and toxicants on populations and communities

open access thumb medium100 100Increased temperature and other environmental effects of global climate change (GCC) have documented impacts on many species (e.g., polar bears, amphibians, coral reefs) as well as on ecosystem processes and species interactions (e.g., the timing of predator–prey interactions). A challenge for ecotoxicologists is to predict how joint effects of climatic stress and toxicants measured at the individual level (e.g., reduced survival and reproduction) will be manifested at the population level (e.g., population growth rate, extinction risk) and community level (e.g., species richness, food-web structure). The authors discuss how population- and community-level responses to toxicants under GCC are likely to be influenced by various ecological mechanisms. Stress due to GCC may reduce the potential for resistance to and recovery from toxicant exposure. Long-term toxicant exposure can result in acquired tolerance to this stressor at the population or community level, but an associated cost of tolerance may be the reduced potential for tolerance to subsequent climatic stress (or vice versa). Moreover, GCC can induce large-scale shifts in community composition, which may affect the vulnerability of communities to other stressors. Ecological modeling based on species traits (representing life-history traits, population vulnerability, sensitivity to toxicants, and sensitivity to climate change) can be a promising approach for predicting combined impacts of GCC and toxicants on populations and communities.

Full reference (link)

Moe SJ, De Schamphelaere K, Clements WH, Sorensen MT, Van den Brink PJ, Liess M. 2013. Combined and interactive effects of global climate change and toxicants on populations and communities. Environ Tox Chem 32(1): 49-61.

The potential for adaptation in a natural Daphnia magna population: broad- and narrow-sense heritability of netreproductive rate under Cd stress at two temperatures

The existence of genetic variability is a key element of the adaptive potential of a natural population to stress. In this study we estimated the additive and non-additive components of the genetic variability of net reproductive rate (R-0) in a natural Daphnia magna population exposed to Cd stress at two different temperatures. To this end, life-table experiments were conducted with 20 parental and 39 offspring clonal lineages following a 2 x 2 design with Cd concentration (control vs. 3.7 mu g Cd/L) and temperature (20 vs. 24 A degrees C) as factors. Offspring lineages were obtained through inter-clonal crossing of the different parental lineages. The population mean, additive and non-additive genetic components of variation in each treatment were estimated by fitting an Animal Model to the observed R-0 values using restricted maximum likelihood estimation. From those estimates broad-sense heritabilities (H-2), narrow-sense heritabilities (h(2)), total (CVG) and additive genetic coefficients of variation (CVA) of R-0 were calculated. The exposure to Cd imposed a considerable level of stress to the population, as shown by the fact that the population mean of R-0 exposed to Cd was significantly lower than in the control at the corresponding temperature, i.e. by 23 % at 20 A degrees C and by 88 % at 24 A degrees C. The latter difference indicates that increasing temperature increased the stress level imposed by Cd. The HA(2) and CVG were significantly greater than 0 in all treatments, suggesting that there is a considerable degree of genetic determination of R-0 in this population and that clonal selection could rapidly lead to increasing population mean fitness under all investigated conditions. More specifically, the HA(2) was 0.392 at 20 A degrees C+Cd and 0.563 at 24 A degrees C+Cd; the CVG was 30.0 % at 20 A degrees C+Cd and was significantly higher (147.6 %) in the 24 A degrees C+Cd treatment. Significant values of h(2) (= 0.23) and CVA (= 89.7 %) were only found in the 24 A degrees C+Cd treatment, suggesting that the ability to produce more offspring under this stressful condition may be inherited across sexual generations. In contrast, in the less stressful 20 A degrees C+Cd treatment the h(2) (0.06) and CVA (7.0 %) were very low and not significantly higher than zero. Collectively our data indicate that both the asexual and sexual reproduction phases in cyclic parthenogenetic D. magna populations may play a role in the long-term adaptive potential of Daphnia populations to chemical stress (with Cd as the current example) and that environmental variables which influence the stress level of that chemical may influence this adaptive potential (with temperature as current example).

Full reference (link)

Messiaen M, Janssen CR, Thas O, De Schamphelaere KAC. 2012. The potential for adaptation in a natural Daphnia magna population: broad and narrow-sense heritability of net reproductive rate under Cd stress at two temperatures. Ecotoxicol 21(7) : 1899-1910.

Biodiversity of freshwater diatom communities during 1000 years of metal mining, land use, and climate change in Central Sweden

Frederik De Laender and colleagues subjected a unique set of high-quality paleoecological data to statistical modeling to examine if the biological richness and evenness of freshwater diatom communities in the Falun area, a historical copper (Cu) mining region in central Sweden, was negatively influenced by 1000 years of metal exposure. Contrary to ecotoxicological predictions, we found no negative relation between biodiversity and the sedimentary concentrations of eight metals. Strikingly, our analysis listed metals (Co, Fe, Cu, Zn, Cd, Pb) or the fractional land cover of cultivated crops, meadow, and herbs indicating land disturbance as potentially promoting biodiversity. However, correlation between metal- and land-cover trends prevented concluding which of these two covariate types positively affected biodiversity. Because historical aqueous metal concentrations—inferred from solid-water partitioning—approached experimental toxicity thresholds for freshwater algae, positive effects of metal mining on biodiversity are unlikely. Instead, the positive relationship between biodiversity and historical land-cover change can be explained by the increasing proportion of opportunistic species when anthropogenic disturbance intensifies. Our analysis illustrates that focusing on the direct toxic effects of metals alone may yield inaccurate environmental assessments on time scales relevant for biodiversity conservation.

Full reference (link)

De Laender F, Verschuren D, Bindler R, Thas O, Janssen CR. 2012. Biodiversity of Freshwater Diatom Communities during 1000 Years of Metal Mining, Land Use, and Climate Change in Central Sweden. Environ. Sci. Technol. 46(16) : 9097-9105.

Identification of pathways, gene networks, paralogous gene families in Daphnia pulex responing to exposure to the toxic cyanobacterium Microcystis aeruginosa

Jana Asselman and colleagues describe in their most recent paper the implementation of a whole-genome expression microarray to identify pathways, gene networks, and paralogous gene families responsive to the toxic cyanobacterium Microcystis in the waterflea Daphnia pulex. They identified four pathways/gene networks and eight paralogous gene families affected by Microcystis. Differential regulation of the ribosome, including three paralogous gene families encoding 40S, 60S, and mitochondrial ribosomal proteins, suggests an impact of Microcystis on protein synthesis of D. pulex. In addition, differential regulation of the oxidative phosphorylation pathway (including the NADH:ubquinone oxidoreductase gene family) and the trypsin paralogous gene family (a major component of the digestive system in D. pulex) could explain why fitness is reduced based on energy budget considerations.

Full reference (link)

Asselman J, De Coninck D, Glaholt S, Colbourne JK, Janssen CR, Shaw JR, De Schamphelaere KAC. 2012. Identification of Pathways, Gene Networks, and Paralogous Gene Families in Daphnia pulex Responding to Exposure to the Toxic Cyanobacterium Microcystis aeruginosa. Environ. Sci. Technol. 46(15) : 8448–8457.