Thesis (M. Sc.), Memorial University of Newfoundland, 1998. / Restricted until November 1999. Bibliography: leaves 93-110.

Aquatic toxicology has been identified as a valuable tool in the identification and management of chemical pollution in aquatic ecosystems. Standardised methodologies for acute aquatic bioassays have been adopted from international agencies. As a result of these standard methods, the use of laboratory cultured organisms for toxicity testing has been more popular than that of indigenous field-caught organisms. Included in these adopted methods are those for the cultured crustacean Daphnia pUlex. D.pulex is adapted to living in standing water and the suitability of this species to determine toxic effects for South African riverine environments, which are largely flowing, has been questioned. Thus this thesis is a case-study ofthe use of D.pulex and indigenous site-specific macroinvertebrates as toxicity test organisms for setting acute water quality guidelines to protect aquatic ecosystems. The study highlights site-specific problems such as reference sites and organism identification. The acute tolerance of selected indigenous invertebrates was compared to that of D. pulex, using both a single-substance reference toxicant (zinc) and selected whole efiluents. The significance of source population and culture age as a potential source of biological variability between D.pulex cultures was also investigated. D.pulex cultures have been initiated in South Africa from females collected from a number of different local populations; also it is assumed that no genetic change (due to mutation) occurs within a D.pulex culture over time. In order to establish if source population and culture age are a source of biological variability between D.pulex experiments, the acute tolerJuce to zinc of two different D.pulex populations and three different generations within a population were compared. Due to experimental variability results were inconclusive, and differences in tolerance as a result of population difference or culture age could not be determined with confidence. The acute tolerance of D.pulex to a single reference chemical (zinc) and selected whole efiluents was compared to that of selected indigenous invertebrates. Acute 48 h D.pulex zinc tolerance (LC50 range: 0.22 - 0.60 mg/l Zn) was found to be more sensitive than acute 96 h tolerances shown by mayfly species A.fconurus peringueyi (Heptageniidae) (LC50: 17.42 mg/l Zn), Euthrauluselegans (Leptophlebiidae) (LC50: 0.98 mg/IZn), Ba~tidae (LC50: 0.94mg/IZn) and shrimp, Caradina nilotica (Atyidae) (LC50: 3.17 mg/l Zn). This result suggests that guidelines for zinc set using D.pulex will protect the selected indigenous invertebrates. Selected whole eftluents were not acutely toxic to either D.pulex or selected indigenous invertebrates. These experiments were used as a case study for method development regarding the comparative use of D.pulex and indigenous invertebrates in acute whole eftluent toxicity testing. Finally, it is recommended that a suite of indigenous organisms (e.g. macroinvertebrates, fish and algae), as well as laboratory cultured D.pulex, be used in the initial setting of guidelines and that D.pulex be used for routine compliance monitoring. It is futher recommended that a suite of available monitoring methods, such as chemical and biomonitoring methodologies, be used in conjuction with toxicity testing in water quality management.

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

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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.

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 current explanation for the absence, or low abundance, of filter-feeding invertebrates from some rocky shores is that because of local variation in nearshore oceanographic conditions, larvae do not arrive in sufficient numbers to establish populations. One putative consequence of this is that macroalgae are able to establish dominance in areas where filter-feeders (especially mussels) do not recruit well. While macroalgae have been transplanted to mussel-dominated shores with varying success, the survival, growth and reproduction of transplanted mussels has not been tested in areas dominated by macroalgae. To determine specifically what tips the balance between shores dominated by filter-feeding invertebrates and those dominated by macroalgae, I monitored the recruitment of intertidal mussels at four sites on the Kaikoura coast: two with mussels present and two algal-dominated. No significant differences in mussel recruitment rates were found between habitats and recruitment intensity at all sites was found to be very low. Recruitment limitation is not the reason for the absence of mussels from algal dominated shores but some form of limitation does occur to reduce the number of arriving mussels. Predation effects were examined by transplanting juvenile mussels into caged, uncaged and control treatments. No significant differences in predation rates between habitats were found and transplanted mussels in open cages at all sites were removed within 3 days. Mobile fish predators appeared to be the most likely cause of this intense predation. Growth of transplanted mussels into algal and mussel habitats was found to be significantly different. Mussels grew faster in mussel dominated habitats and after 6 months in algal dominated habitats, all mussels had died. The outcome of these experiments indicates that there is a close relationship between recruitment, survival and growth which tips the balance and allows the existence of mussel beds along the Kaikoura coastline.

<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.