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Acute toxicity tests with selenium were conducted with three freshwater species. All data are expressed as selenite-selenium. Daphnia pulex had a 48 hr LC50 of 3.87 mg/l selenium. The 96 hr LC50 and EC50O values for Gambusia affinis and Physa sp. respectively, were 12.56 and 27.08 mg/l selenium. The sublethal effects of 0.2, 0.4, 0.6 and 0.8 mg/1 selenium on survival, growth and reproduction of Daphnia pulex were monitored for twenty-eight days. These results were analyzed statistically by brood. Appreciable mortality only occurred at 0.8 mg/l selenium. Growth, as measured by body length, was depressed at the highest concentration during the early instars and was slightly stimulated during the later instars. Number of live young per brood was depressed at 0.4, 0.6 and 0.8 mg/l selenium during the early broods and may have been stimulated in later broods. Reproductive dysfunction (i.e., dead young, deteriorated eggs, and abortions) only was significant at the higher concentrations in the early broods. It appeared that the Daphnia were acclimating to the selenium stress. Based on these studies, the MATC for selenite-selenium was 280 ug/l. The effects of selenium on oxygen consumption and filtering rate during 24 hr exposure were also tested at the above concentrations. There were no significant effects of selenium on oxygen consumption. Selenium slightly stimulated filtering rate at 0.2 mg/l and depressed it at the higher concentrations. An evaluation of the water quality criteria for selenium in fresh water indicates that all of the methods for deriving these proposed criteria are inadequate. Based on my evaluation a dual criterion seems appropriate: a strict criterion for selenate-selenium and lenient criterion for selenite- and biselenite-selenium. / Master of Science

The purpose of this study was to assess the effects of water-soluble fractions (WSF) of naphthalene, phenanthrene, No. 2 fuel oil, and coal-tar creosote on the survival, growth, reproduction, feeding, and metabolism of Daphnia pulex. The 48 hr LC50 values after acute exposure (as percent WSF) for creosote, No. 2 fuel oil, phenanthrene and naphthalene were 2.91, 34.10, >>100, and 57.52 percent, respectively. Gas chromatography analysis indicated naphthalene and phenanthrene 48 hr LC50 values (as mg/1) were 2.92-3.89 and 0.96-1.28, respectively. Up to 40 peaks were noted in each stock WSF of creosote and No. 2 fuel oil. For chronic studies, young (24 hr) Daphnia were exposed to calculated LC20 and LC30 concentrations of WSF's for their entire life. The LC30 concentrations of creosote and phenanthrene showed a significant reduction in growth rate and number of live young, as well as reduced number of broods, impairment of molting, and significant delay in reproductive maturation; instances of possible neoplasms were also noted in one organism from each of these test groups. No. 2 fuel oil produced similar effects on growth and reproduction, but results were not as significant. Increased longevity and slight reduction in growth rate were noted for both naphthalene test groups. The effects upon oxygen consumption after exposure to test WSF's were variable. The LC30 concentration of creosote and both naphthalene concentrations were significantly different from each other; both naphthalene concentrations elicited the lowest oxygen consumption rates recorded, while the creosote LC30 group exhibited the highest rate of oxygen consumption. However, no experimental means were significantly different from controls. Highly significant differences existed between filtering rates of organisms after exposure to the WSF's. The LC20 concentrations of creosote and phenanthrene produced the highest and lowest filtering rates, respectively. Both oil test groups demonstrated significantly higher filtering rates. Monitoring zooplankton filtering rates appears to be a promising parameter to evaluate physiological stress on these organisms. This chronic study and data from other comparable chronic studies indicate that the length of a pre-adult Daphnia after 7 days of exposure to stress can be used to predict chronic reproductive effects with the same degree of accuracy as the 21-day test. Adoption of this test would eliminate difficulties with starvation, nutrition, and competition for food which contribute to the variability in reproductive impairment tests. A possible mechanism of action of polynuclear aromatic hydrocarbons upon endocrine systems is strongly suggested by the dramatic and diverse effects upon growth and reproduction in Daphnia pulex. / Ph. D.

<p>Understanding the processes that shape the spatial distribution of genetic variation within species is central to the evolutionary study of diversification and demography. Neutral genetic variation reflects past demographic events as well as current demographic characteristics of populations, and the correct interpretation of genetic data requires that the relative impact of these forces can be identified. Details of breeding systems can affect the genetic structure through effects on effective migration rate or on effective population size. Restrictions in recombination rate lead to associations between neutral marker genes and genes under natural selection. Although the effects on genetic structure can be substantial, the process will often be difficult to tell apart from stochastic effects of history or genetic drift, which may suggest erroneous conclusions about demography.</p><p>In cyclically parthenogenetic freshwater invertebrates, which alternate between sexual and asexual reproduction, demographic fluctuations and reliance on diapausing eggs for dispersal enhances neutral genetic differentiation as well as effects of selection on associated genes. Although genetic founder effects are expected to be profound and long-lasting in these species, genetic hitch-hiking may reduce initial strong differentiation rapidly if better adapted genes are introduced by mutation or immigration. Fluctuating environmental conditions have been suggested to generate rapid shifts in the frequencies of clones during the asexual phase. In the presence of egg banks resting in sediments, genetic diversity is stabilised and the importance of migration for differentiation is reduced.</p><p>Studies of unstable and young populations of cyclically parthenogenetic <i>Daphnia pulex</i> showed substantial variation for important fitness traits, within as well as between populations, despite hypothesised recent founder effects. Neutral markers indicated genetic equilibrium, but changes in clonal composition during asexuality disrupted the genetic structure in a manner compatible with local adaptation and exclusion of immigrants. This illustrates that the forces affecting sexual progeny may be markedly different from those shaping the structure among asexual individuals.</p>

Understanding the processes that shape the spatial distribution of genetic variation within species is central to the evolutionary study of diversification and demography. Neutral genetic variation reflects past demographic events as well as current demographic characteristics of populations, and the correct interpretation of genetic data requires that the relative impact of these forces can be identified. Details of breeding systems can affect the genetic structure through effects on effective migration rate or on effective population size. Restrictions in recombination rate lead to associations between neutral marker genes and genes under natural selection. Although the effects on genetic structure can be substantial, the process will often be difficult to tell apart from stochastic effects of history or genetic drift, which may suggest erroneous conclusions about demography. In cyclically parthenogenetic freshwater invertebrates, which alternate between sexual and asexual reproduction, demographic fluctuations and reliance on diapausing eggs for dispersal enhances neutral genetic differentiation as well as effects of selection on associated genes. Although genetic founder effects are expected to be profound and long-lasting in these species, genetic hitch-hiking may reduce initial strong differentiation rapidly if better adapted genes are introduced by mutation or immigration. Fluctuating environmental conditions have been suggested to generate rapid shifts in the frequencies of clones during the asexual phase. In the presence of egg banks resting in sediments, genetic diversity is stabilised and the importance of migration for differentiation is reduced. Studies of unstable and young populations of cyclically parthenogenetic Daphnia pulex showed substantial variation for important fitness traits, within as well as between populations, despite hypothesised recent founder effects. Neutral markers indicated genetic equilibrium, but changes in clonal composition during asexuality disrupted the genetic structure in a manner compatible with local adaptation and exclusion of immigrants. This illustrates that the forces affecting sexual progeny may be markedly different from those shaping the structure among asexual individuals.

Determining the molecular basis of heritable variation in complex, quantitative ecologically important traits will provide insight into the proximate mechanisms driving phenotypic and ecological variation, and the molecular evolutionary history of these traits. Furthermore, if the study organism is a “keystone species” whose presence or absence shapes ecological communities, then we extend our understanding of the effects of molecular variation to the level of communities. I examined the molecular basis of variation in 32 ecologically important traits in the freshwater pond keystone species Daphnia pulex, and identified thousands of candidate genes for which variation may affect not just Daphnia phenotypes, but the structure of communities. I extended the basic results to address two questions: what genes are associated with the offspring size-number trade-off in Daphnia; and can we identify candidate “keystone gene networks” for which variation may have a particularly strong influence on eco-evolutionary dynamics of limnetic communities? I found that different genes, with different biological functions, are associated with the trade-off in subsequent broods, and propose a model linking evolutionary frameworks to molecular biological functions. Next I found that quantitative genetic variation in keystone traits appears to co-vary with the selection regimes to which Daphnia is subject, and identified two candidate gene networks that may underpin this genetic variation. Not only do these results provide a host of molecular hypotheses to be tested as Daphnia matures as a model genomic organism, but they also suggest models that link molecular research with broader themes in ecology, evolution, and behavior. / text

Chemical communication in aquatic organisms has been topic of a large number of studies focusing interactions between organisms via info chemicals. Diel Vertical Migration (DVM) is commonly observed among zooplankton and consists of a single daily ascent with minimum depth reached between sunset and sunrise and a descent with maximum depth attained during the day. DVM was absent or reduced when predators were absent and well developed in their presence. Species of the Daphnia are one of the well investigated group in freshwater environments. Variation in DVM of Daphnia in response to fish kairomone is one of the best studied behavioral strategies. Kairomone, as a term, is described interspecific chemical messengers, the adaptive benefit of which falls on the recipient rather than the emitter. As a result, nature and origin of kairomone is still unclear and needs to be investigated. It was decided that FT-IR technique would be favorable tool for this aim. In this frame, it was conceived that the occurrence of migration adaptation relevant to the seasonal changes in the presence of fish kairomone could be proved and characterized by FT-IR technique. Results of the present study indicate that non-aromatic, secondary amine compound has significant contribution to fish cue. Since other sources other than fish can contribute the natural amine compounds level in fresh water environment, origin and concentration of amines are needed further investigation to determine ecological function of amine.

Thermal adaptation in freshwater planktonic crustacean Daphnia pulex has been investigated by means of heatshock (35°C) experiments using individuals acclimated to different water temperatures (18, 24, and 28°C). Retention of mobility and survival during the heatshock experiments differed among clones and strongly depended on acclimation temperature: clones acclimated to substressful temperature (28°C) survived significantly longer than clones acclimated to lower temperatures. Both retention of mobility and survival correlated with geographic latitude of the clones' origin. There was, on the other hand, no significant correlation between clones' performance in heatshock experiments and hemoglobin content. Clones do not differ in the degree of the effect of acclimation on survival during heatshock but differ with respect to the effect of acclimation on mobility retention.

The response of aquatic species to contaminants is often context dependent as illustrated by the influence that predation cues can have on the toxicity of some chemicals. We sought to gain additional insight into this interaction by examining how predation cues (alarm cue and fish kairomone) influence metabolic rate and the acute toxicity of sodium chloride and cadmium to fathead minnow larvae (Pimephales promelas) and sodium chloride to Daphnia pulex neonates. Consistent with a “flight or fight” response, the metabolic rate of fish larvae was elevated in the presence of alarm cue and growth of the minnows was also significantly reduced when exposed to alarm cue. The average 48-h LC50 for fathead minnows exposed to sodium chloride was significantly lower in the presence of alarm cue and kairomone combined as compared to tests with the salt alone. Analysis of the dose and survival response indicated alarm cue increased sensitivity of the fish to mid-range salt concentrations in particular. These results suggest an energetic cost of exposure to predation cues that resulted in enhanced toxicity of NaCl. Exposure to kairomone alone had no significant effect on salt toxicity to the minnows, which could be related to a lack of previous exposure to that cue. The acute toxicity of cadmium to the fish larvae was also not affected by the presence of predation cues which could be due to a metal-induced sensory system dysfunction or reduced bioavailability of the metal due to organic exudates from the predation cues. In contrast to the fathead minnow results, the metabolic rate of D. pulex and toxicity of NaCl to the daphnids were reduced in the presence of certain predator kairomones. This suggests an anti-predator response that enhanced tolerance to the salt. This study illustrates that the effect of predation cues on toxicity of aquatic contaminants can vary significantly based on the prey species, type of cue, and chemical stressor.

<p> In this study the influence of several water chemistry parameters on the toxicity of Ni to Daphnia pulex in soft water were tested. A reconstituted soft water (pH 7.8, hardness 31.5 mg/L CaCO3) was used as the basis for culture and testing. Daphnia pulex was chosen as a typical cladoceran, one which can be acclimated to very soft water. An understanding of the influence of water chemistry on Ni toxicity in soft water is relevant because metals have higher bioavailability in soft water. The 48h EC50 in the reconstituted soft water (RSW) was 974 μg/L (16 μM) dissolved Ni (95%CI 830- 1081 μg/L). The following factors were examined for their potential for modifying Ni toxicity: Ca, Mg, Na, K, Cl, pH (3 different approaches used) and natural organic matter (NOM, 2 sources tested). Both Ca and Mg protected against Ni toxicity and the relative effect was greater for Ca. Varying the concentrations of Na, Cl or K did not alter the toxicity of Ni. Tests at different pH showed that as pH increased, Ni toxicity decreased. When the test solution pH was adjusted with the organic buffer 3-morpholinepropanesulfonic acid, there was a clear correlation between increasing pH and increasing EC50. The pH tests using bicarbonate to adjust pH did not show this relationship as clearly. Both types of NOM showed a protective effect on Ni toxicity with Nordic Reservoir NOM having a 4 fold greater effect than that of Suwannee River NOM. This research illustrated that the effect of alterations in water chemistry were generally as predicted within the context of the biotic ligand model (BLM) approach. The data provide the information required to develop a BLM for the acute effects of Ni in soft water.</p> / Thesis / Master of Science (MSc)