Unprecedented rates of anthropogenic environmental change have resulted in dramatic decreases in biodiversity worldwide. In order to persist during changes in both the abiotic and biotic environment resulting from anthropogenic stressors such as climate change and habitat degradation, populations must be able to respond or face extirpation. Predicted population-level responses to environmental change include i) range shifts as individuals disperse into more suitable regions, ii) phenotypic plasticity allowing for shifts in the mean phenotype of the population or iii) microevolution resulting from a genetic change within the population. The goal of this thesis is to assess how species within a community respond to a dramatic change in the environment. This study used the sediment record of a Subarctic pond to investigate the impacts of a rapid increase in salinity on two species of the crustacean zooplankton Daphnia. One species, Daphnia tenebrosa, was unable to persist in the high salinity conditions and is believed to have been extirpated from the system. The other species, Daphnia magna, was tolerant of the new environmental conditions and was present throughout the sediment record. To investigate the changes in life history of D. magna, resting eggs from the sediment were hatched to compare iso-female lines from pre- and post-disturbance time periods. No differences were observed between the clone lines, suggesting that phenotypic plasticity allowed D. magna to persist despite the rapidly changing environmental conditions, and that microevolution in salinity tolerance may not have occurred in this population. This study suggests that, in environments with moderate levels of post environmental change, pre-existing phenotypic plasticity may play a greater role than microevolution in species response to environmental changes. However, not all species from a community display the same response to environmental changes, as seen in this study with the extirpation of D. tenebrosa. To better understand how communities will be affected by future environmental change, further investigations need to be made on what factors influence species response. Identifying species response may allow conservation efforts to focus on species that are unlikely to adapt to environmental change, and are most at risk. / Thesis (Master, Biology) -- Queen's University, 2013-09-29 21:54:34.881

Ce travail avait pour objectif d’étudier les effets de l’uranium sur le budget énergétique et la dynamique de population d’un micro-crustacé représentatif des écosystèmes aquatiques d’eau douce, Daphnia magna. L’étude expérimentale de la toxicité de l’uranium sur la physiologie (nutrition, respiration) et l’histoire de vie (survie, croissance, reproduction) deD. magna a été réalisée au travers d’expositions sur une, deux ou trois générations successives(F0, F1, F2), commencées avec des néonates issus de 1ère ou 5ème ponte, à des concentrations de0, 10, 25 et 75 μgU.L-1. Les résultats ont mis en évidence l’aggravation des effets au travers des générations (en partie liée à l’exposition des daphnies pendant l’embryogénèse) et la sensibilité plus forte des individus issus de 1ère ponte. Des réductions significatives des taux d’assimilation mesurés par méthode de marquage-traçage au 14C de la nourriture nous ont permis d’identifier un effet sur l’assimilation comme mode d’action de l’uranium, en accord avec les altérations importantes de la structure de la paroi du tube digestif révélées par microscopie optique.L’intégration des résultats dans un modèle de budget énergétique (DEBtox) a abouti à l’estimation de concentrations seuil sans effet (NEC) de 9.37, 8.21 et 2.31 μgU.L-1 au-delà desquelles le fonctionnement de l’organisme est altéré dans les générations F0, F1 et F2,respectivement. La combinaison du DEBtox avec des modèles matriciels a permis d’extrapoler les conséquences sur le taux de croissance asymptotique de la population (λ), critère plus pertinent dans un contexte écologique. Les simulations ont prédit une augmentation de l’impact de l’uranium au travers des générations avec une réduction de λ dans F0 et une extinction des populations pour des concentrations de 51-59 μgU.L-1 dans F1 et de 39-41 μgU.L-1 dans F2. Les simulations ont souligné l’importance de prendre en considération les individus les plus sensibles dans la détermination de la réponse des populations. / This work aimed to study effects of uranium on energy budget and population dynamicsin Daphnia magna a representative microcrustacean of freshwater ecosystems. An experimentalstudy of uranium toxicity on physiology (nutrition, respiration) and life history (survival, growthand reproduction) of D. magna was carried out, based on exposures over one, two or threesuccessive generations (F0, F1 and F2) started with neonates from 1st or 5th brood, at 0, 10, 25and 75 μgU.L-1. Results showed that toxic effects increased across generations (partially due todaphnid exposure during embryogenesis) and that individuals from 1st brood were moresensitive than individuals from 5th brood. Significant reductions in assimilation rates, measuredusing a radiotracing method with 14C-labelled food, allowed us to identify an effect onassimilation as the mode of action for uranium, in agreement with important damages in theintegrity of intestinal epithelium observed by optic microscopy. Integrating results in a dynamicenergy budget model (DEBtox) yielded estimated no effect concentrations (NEC) of 9.37, 8.21and 2.31 μgU.L-1 above which organism functions were altered in generations F0, F1 and F2,respectively. Combining DEBtox with matrix models allowed us to extrapolate consequences onasymptotic population growth rate (λ), a relevant endpoint in an ecological context. Simulationspredicted an increase in uranium impact across generations with reduction of λ in F0 andpopulation extinctions at 51-59 μgU.L-1 in F1 and 39-41 μgU.L-1 in F2. Simulations emphasizedthe importance of considering the most sensitive individuals while determining populationresponse

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.

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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>