This thesis focuses on ecological processes among plankton organisms. It especially questions the influence of food quality on growth and survival of freshwater plankton. I focused on the influence of various ratios of nitrogen and phosphorus in available food. I am also interested in finding out the food requirements of chosen consumer Daphnia longispina. Within this broad topic, I specify a question, whether various quality and quantity of food influences the life history parameters of the species Daphnia longispina and whether the absence of common species of Cladoceran Daphnia longispina in Plešné Lake is caused by unsuitable quality of food. I have bred Daphnia longispina in laboratory conditions for two years. I fed it by algae Monoraphidium dybowskii isolated from Plešné Lake and grown in two media P-limited (C:P 1174), P-unlimited (C:P 290) and three concentration (1,2, 4 mg C/L). Cladocerans fed by food from medium that had a C:N:P ratio approximately the same as can be found in Plešné Lake (C:P 1174) lived for a singificantly shorter period of time and during the experiment they did not reproduce even in the case with the largest amount of food (4 mg C/L). This is a possible reason why Daphnia longispina did not return to Plešné Lake after the period of strong acidification, climax of...

Freshwater zooplankton crustacean Daphnia frequently face strong temperature fluctuations in its natural environment, which necessitates adaptive plastic responses. This study focuses on changes in lipid peroxidation and total oxidative capacity in Daphnia tissues in response to long-term and short-term temperature changes. Long-term acclimation to 28ºC helped Daphnia survive longer at lethally high temperatures. This difference, however, was not accompanied by changes in lipid peroxidation, indicating that it isn’t a good measure of damage or predictor of temperature tolerance. On the other hand, total oxidation capacity was lower 28ºC- than in 18ºC-acclimated Daphnia, suggesting that acclimation resulted in higher amounts of antioxidants in Daphnia tissues. Exposure to hypoxia, known to up-regulate antioxidant pathways in Daphnia, further elevated heat tolerance in 28ºC- acclimated individuals. Yet, manipulations of glutathione, an important antioxidant, while predictably affecting oxidative capacity, didn’t influence heat tolerance in Daphnia, suggesting that other antioxidants may play a significant role in it.

No description available.

This thesis examines the toxicity of the herbicide glyphosate (two formulations ¡V technical grade and Roundup Biactive RB) and the insecticide chlorpyrifos CPF to a model freshwater food chain of a producer and consumer. The importance of studying the toxicity of low (environmentally realistic) concentrations of pesticides to non-target organisms is highlighted. An extensive literature review on the toxicity of glyphosate and chlorpyrifos to aquatic organisms is provided. The requirements for the maintenance of algal (Chlorella vulgaris, Chlorella pyrenoidosa and Pseudokirchneriella subcapitata) and Daphnia carinata cultures are discussed. The effects of two formulations of the herbicide glyphosate (technical grade and Roundup Biactive„µ) and the insecticide chlorpyrifos on the growth of Chlorella pyrenoidosa and Pseudokirchneriella subcapitata were studied, and the EC50 values determined. Hormesis was observed when P. subcapitata was exposed to concentrations of Roundup equal to 7% and 4% of its EC50 respectively. When exposed to chlorpyrifos concentrations 0.3-5 ƒÝg/L, hormesis was observed for both algal species with a maximum at 0.06% of EC50. The effects of sublethal concentrations of chlorpyrifos on population characteristics of Daphnia carinata were investigated in multiple-generation toxicity testing using individual culture. Exposure to chlorpyrifos affected survival and fecundity of animals in the first generation. In the second generation the most affected endpoint was time to the first brood with an indication of hormesis. LC50 tests were then conducted using animals of the third generation from each of the exposures in individual tests. Results of testing the third generation showed a constant significant decline in LC50 in the order of control daphnids through to ¡¥0.1 LC50¡¦ pre-exposed daphnids. The same experimental protocol was used in testing of glyphosate (technical grade and Roundup Biactive). Glyphosate was tested in two different media: sea salt solution and M4 medium, while Roundup Biactive was tested in M4 medium. Results indicated that glyphosate and Roundup Biactive had low toxicity to Daphnia. Hormesis was evident in sea salt medium exposures in the first and second generations of daphnids with glyphosate. When exposed to glyphosate and Roundup Biactive in M4 medium animals showed no indication of hormesis. It is hypothesized that glyphosate may have compensated for the lack of microelements in the sea salt medium, and possible mechanisms discussed.The modifying effect of glyphosate on the toxicity of cadmium to Daphnia carinata was studied using the same experimental design. Low concentrations of Roundup Biactive reduced the toxicity of cadmium, and the performance of daphnia was enhanced in terms of animal size, survival, fecundity, and the rate of natural increase in both generations in the presence of glyphosate. However when the third generation was tested for their sensitivity to Cd in the 48-h LC50 experiments there was no difference between RB-free and RB-spiked treatments in pair wise comparisons, indicating that no adaptation mechanisms were involved in the enhancement. The implications of these observed effects for environmental freshwater food chains subjected to pesticide exposure are discussed and recommendations on modifying pesticide use are provided.

Thesis (M.S.)--Baylor University, 2005. / Includes bibliographical references (p. 61-68).

As Daphnia have an important role in freshwater food webs, it is important to understand how environmental stressors affect their survival and life history traits. Daphnia pulex were first acutely exposed to a combination of NaCl salinities (0.00-10.0 g/L) and fish-exuded kairomone. The 24 and 48 hour LC50 values were 0.401 and 0.159 g/L in kairomone-absence and 1.962 and 1.007 g/L in kairomone-presence. Hence, survival decreased with increasing salinity, while the kairomone enhanced daphnid resistance to salinity below 2 g/L. During the chronic exposure to salinity (0.00-1.5 g/L) combined with the fish-exuded kairomone, impacts of temperature and food were also investigated. Survival decreased significantly with increased salinity, while the kairomone had a positive impact on survival at intermediate salinity levels, suggesting an antagonistic relationship. Temperature alone had a significant negative impact on survival and its combined effect with salinity and fish kairomone was synergistic. However, the impact of food limitation was insignificant. Life history parameters were affected by both salinity and the fish-exuded kairomone, the combination of which significantly decreased the body length: width ratio. Egg number/individual decreased with salinity and increased in the presence of the fish kairomone. In conclusion, the combined impact of salinity and fish-exuded kairomone significantly affected daphnid survival and life history traits in a non-linear manner, such that fish kairomone enhanced daphnid resistance to intermediate salinity levels. Moreover, the combined effect of salinity, temperature and fish kairomone on daphnid survival was also significant.

Thesis (M. Sc.)--York University, 2007. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 83-99). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004 & res_dat=xri:pqdiss & rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation & rft_dat=xri:pqdiss:MR31989.

The use of biomarkers is considered a promising alternative, or complement, to traditional ecotoxicological assays. Toxic effects are often initially manifested at the molecular or biochemical level, biomarkers are therefore used as sensitive indicators of toxic exposure. Ideally, biomarkers would also indicate reduced fitness and possible later effects at the individual or population levels. However, implementing biomarkers in ecotoxicology is challenging and few biomarkers have an established connection to reduced individual fitness. The aim of this thesis was to increase the value and improve the interpretation of biomarker responses in ecotoxicological studies by examining the impact of confounding factors and the relationship between oxidative biomarkers and reproductive effects in crustaceans. The sensitivity of biomarkers was confirmed in paper I as toxic effects of pharmaceuticals with conserved drug target orthologs were observed at the molecular and biochemical levels both earlier and at lower concentrations than effects on mortality and reproduction. No toxic effects were observed for the pharmaceutical without identified drug target orthologs, thus stressing the importance of considering toxic mechanisms and being aware of the most likely target when evaluating toxic effects also in non-target species. Many xenobiotics and environmental stressors interfere with oxidative processes, making oxidative biomarkers interesting to study in ecotoxicology and stress ecology. Still, feeding rate was identified as a confounding factor for antioxidant capacity (assayed as oxygen radical absorbance capacity, ORAC) and lipid peroxidation in ecotoxicological studies (paper II). However, ORAC normalized to protein was independent of altered feeding rates, hence it can be applied as a suitable exposure biomarker without considering alterations and effects of feeding rate. The connection between reproduction and oxidative stress is dual, as reproduction both can be inhibited by oxidative stress and induce pro-oxidative processes. Further, a positive association was found between ORAC and the occurrence of embryo aberrations in the benthic amphipod Monoporeia affinis (paper III). An association between antioxidant defense and reproduction was also observed for Daphnia magna (paper IV). Threshold values for identification of exposed individuals and prediction of possible later reproductive effects were established for ORAC. This thesis has contributed to diminishing some of the knowledge gaps limiting the use of oxidative biomarkers in ecotoxicology, by contributing to increased understanding of how oxidative biomarkers relate to important life-traits. Moreover, ORAC has been identified as a suitable biomarker of not only exposure, but also reproductive effects. Future research should continue to establish connections between biomarker responses and effects at higher levels, and focus on providing defined threshold values to enable predictions about later effects. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

In many habitats, species’ traits correspond strongly to local environmental conditions. The cause of this pattern may be in-situ evolution, where initially mal-adapted resident species evolved traits that increased their fitness. Alternatively, species with suitable traits may have colonized the focal habitat and replaced resident species. Since theories in the fields of evolutionary biology and community ecology developed independently, few guidelines tell us when to expect evolutionary adaptation or ecological species replacement as the primary driver of species and trait composition in a given habitat. The goal of my dissertation research was to explain how evolutionary adaptation and ecological species replacement together determine the composition of pond zooplankton communities. I combined theoretical models with thorough surveys of natural pond communities and manipulative experiments. I discovered that one particular zooplankton species, Daphnia pulex, evolved to have different trait values in ponds with different environments. The evolutionary divergence within D. pulex profoundly affected its ecological interactions with other zooplankton species. D. pulex populations diverged from one another so much that they differed in their ability to successfully colonize ponds full of competing zooplankton species. I also used a computer simulation model to determine when a community’s trait changes were explained by evolutionary adaptation or ecological species replacement. The dispersal rate of species among habitats and the amount of genetic variance within these species both influenced adaptive trait change in a community. The group of research studies that indicate evolutionary and ecological processes operate on a similar time scale is small but growing. My dissertation research provides another crucial demonstration that evolution within individual species, such as D. pulex, influences their community ecological interactions with other species. I also identified key parameters (dispersal rate among and genetic variance within species) that may help biologists predict whether evolution or ecological species replacement explained adaptive trait change. My projects mostly concern the community and trait distributions that result from the assembly of species in new habitats. However, this framework may inform studies of community response to environmental changes such as invasive species or habitat destruction. / text

Freshwater lake ecosystems often exhibit strong oxygen, and temperature gradients across which many zooplankton species live. Daphnia sp. vary in their ability to up-regulate hemoglobin in response to low oxygen environments. However; the role that hemoglobin up-regulation plays in diel vertical migration, and how it might mediate coexistence of Daphnia within lakes is still unclear. Using an oligotrophic lake in Ontario, I studied three distinct phenotypes of Daphnia pulicaria, which differed in the ability to up-regulate hemoglobin (classified as red, pink, and pale). Twenty-four hour surveys were conducted during the fall of 2012 and samples were drawn at 1m intervals to monitor changes in diel vertical migration. At each 1m interval Daphnia were color indexed, photographed, and preserved for genetic analysis using cellulose acetate electrophoresis. Red and pink Daphnia showed little change in distribution over the water column through time, suggesting individuals experienced little vertical migration. Pale individuals showed strong changes in vertical distribution through time suggesting vertical migration. The phenotypes are strongly correlated with multi-locus genotypes, suggesting genetic differences in migration behavior. Mesocosm experiments were used to manipulate migration over heterogeneous environments to test the hypothesis that vertical migration impacts genetic and phenotypic diversity in Daphnia pulicaria. The first mesocosm experiment contained two treatment groups; a migrating and non-migrating treatment containing the three phenotypes. The migrating treatment permitted unrestricted movement throughout the water column, and the non-migrating treatment restricted Daphnia to discrete 1m intervals. The second mesocosm experiment comprised two non-migrating treatments; red non-migrating and pale non-migrating. Results from the first set of mesocosm experiments indicate decreased genetic and phenotypic diversity in the migrating treatment. Shifts in hemoglobin up-regulation between pales and reds in the second mesocosm experiments suggest hemoglobin up-regulation is plastic, whereby pale, pink, and red individuals have the ability to up and down regulate hemoglobin. The differences in Daphnia migration patterns and the plastic response in hemoglobin up-regulation permits migrating genotypes to withstand low oxygen conditions. Overall implications of this study suggest that migration over a strong environmental gradient plays a key role in fostering phenotypic plasticity and genetic diversity in organisms living in heterogeneous environments. / Thesis (Master, Biology) -- Queen's University, 2014-04-08 12:07:42.757