Determining the extent to which parasites influence natural populaions of hosts is a major focus of studies in parasitology. Addressing this issue requires host-parasite systems that can be monitored under natural conditions and can be manipulated in the laboratory. I study a model system involving the larval trematode Ornithodiplostomum ptychocheilus that encysts in the brains of its intermediate host, the fathead minnow (Pimephales promelas). This parasite was the most common and abundant of 13 other parasites found in minnows in four boreal lakes in Alberta, Canada. In two of these lakes, prevalence of infection reached 100% in most years and mean intensity ranged from 4 to 40 parasites/host. Field and laboratory experiments showed that the size, the rate of parasite development, and time to encystment were intensity-dependent. However, parasite intensity had no effect on host or parasite survival after a simulated winter in the laboratory. One effect of infection was that infected fish and significantly greater cranial heights and widths than controls. The expression of this parasite-induced alteration in host phenotype was dependent on the size of the fish at infection and on parasite intensity. The cranial distortion led to significantly higher mortality of fish maintained on poor diets and altered the host's phototactic response. / ix, 131 leaves : ill. (some col.), map ; 29 cm.

A wide variety of parasites are known to cause changes in host behaviour. The altered behaviours range from simple changes in features such as activity and phototaxis, to the creation of behaviours that are new, and often bizarre. In this study, I investigated the effect of a trematode parasite, Ornithodiplostomum ptychocheilus (Strigeidae; Diplostomidae), on the behaviour of its intermediate host, the fathead minnow (Pimephales promelas). The larval stage (metacercaria) of this parasite resides within the central nervous system, specifically the optic lobes. In fish, one of the main functions of the optic lobes is to receive visual stimuli from the retina and then coordinate the optomotor response (OMR). This response is an innate component of rheotaxis that plays an important role in motion detection, navigation and orientation. In an initial experiment, 16 wk-old metacercariae reduced minnow OMR by 42% compared to uninfected controls. However, in a follow-up experiment, it was 2- and 4- wk old metacercariae that caused the greater (39 and 41% respectively) decrease in OMR. Because 2- and 4-wk old metacercariae are not infective to birds (the next host in the life-cylce), alterations in minnow OMR at this time are unlikely to be a parasite adaptive. During this period, reduced OMR is more likely a result of pathology caused by developing larvae within the optic lobes. However, negative effects of infection on OMR performance persisted to 16 wk post-infection indicating the parasite-induced reduction in host performance could be an adaptive strategy to increase parasite transmission. Surprisingly, the magnitude of reduction in minnow OMR was only loosely linked to metacercarieae intensity. Although both low (<5 parasites/fish), and high intensities (>100) led to large decreases in OMR, intermediate intensities had only a small effect. Such non-linearity between intensity and the magnitude of host behavioural changes suggest that the mechanisms leading to altered host behaviours are varied, and complex. / vii, 79 leaves : ill. ; 29 cm.

The population dynamics and life histories of two larval parasites of fathead minnows were investigated, together with their effects on host reproduction in natural populations. In two lakes in northern Alberta, Canada, 100% of fathead minnows (Pimephales promelas) are infected with larval trematodes (Ornithodiplostomum ptychcocheilus and Posthodiplostomum minimum) that encyst in their brains and mesentaries, respectively. The numbers of parasites in individual adult minnows varied extensively between and within two different lakes. Parallel laboratory studies indicated that selection imposed by common hosts in the life cycles of these species have shaped broadly similar life histories. Field collections of male minnows indicated that early in the breeding season, breeding males were longer than non-breeding males. Furthermore, breeding males had larger girths (independent of total length) and contained fewer numbers of three of 4 common larval trematodes than non-breeding males throughout the breeding season. These parasites most likely affect a male's ability to compete for or defend a nest. / vi, 99 leaves : ill. ; 28 cm.

No description available.

Exposure of fourth instar Aedes aegypti larvae to graded concentrations of the entomopathogenic cercariae of the digenean Plagiorchis elegans, induced fundamental changes in the partitioning of time among a number of major behavioural activities. In the absence of the parasite, swimming, breathing and feeding remained stable over time. Grooming was rarely observed. In the presence of cercariae, larvae increased grooming 26-fold. Concomitantly, feeding was reduced to 33% of control values. Times spent swimming and breathing remained unchanged. The increase in grooming activity was attributable to the attachment of cercariae to the surface of the mosquito larvae, but was independent of infection. Grooming reduced cercarial penetration. Seventy-five percent of cercariae were lost to predation by larvae, but their caloric value was insignificant and failed to compensate for the loss of feeding time due to grooming. The findings are discussed in the context of their impact on larval growth, development and survival.

In an attempt to supply sanitation to the growing communities in rural and peri-urban areas around Durban, the eThekweni Municipality has installed urine diversion (UD) toilets which have been modified to suit local conditions . These toilets are based on the ecological sanitation (EcoSan) system. The future aims are to reuse waste as a composting medium and minimize the use of water but the presence of microorganisms in the faecal waste poses a potential health risk to people in contact with it. Currently the Municipality has not deemed the waste safe for re-use but has suggested that after a one year standing period it should be free of all potential pathogens including Ascaris lumbricoiodes (human roundworm) ova. This study reports on the development of the AMBIC protocol for the recovery of Ascaris ova from the standing vaults of UD toilets. The protocol has been shown to consistently recover over 70% of Ascaris ova and has the added advantage of recovering the ova of other helminth species (Trichuris trichiura and Taenia sp.) present in a UD standing vault sample. Recoveries of Ascaris ova and ova of other parasite species, namely Trichuris and Taenia sp., are reported from waste which has been standing for one year. This is cause for concern as it shows one year is not a sufficient standing period to render the waste free of all microorganisms. Sampling from 124 UD toilet vaults that were in use, showed a high prevalence of both helminth (Ascaris lumbricoiodes, Trichuris trichiura and Taenia sp.) and protozoan (Giardia and Cryptosporidium) parasites. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2009.

Cercariae of the digenean Plagiorchis elegans cause high levels of morbidity and mortality among larvae of Aedes aegypti . The impact of this parasite on the larval population dynamics of the experimental host as mediated through intraspecific competition, egg hatchability and ovipositional preference was assessed by calculating the probability of pre-imagos to develop from one stage to the next, or to die within consecutive 24 h intervals. Attractiveness of the water to ovipositing females in a dynamic larval population was not affected by exposure to the parasite, but varied significantly over time, regardless of food abundance. In optimally fed populations, these changes were positively correlated with pupal production, but were not affected by early instar development. Most of the entomopathogenic effects of the parasite were expressed in the pupal stage. Thus, exposure to the parasite significantly reduced adult emergence, but did not greatly impair pre-imago development. Nonetheless, exposure to various levels of the parasite significantly increased mortality of all larval stages. Suboptimally fed larval populations displayed severely impaired development and produced few adults. Exposure to P. elegans increased adult production slightly, suggesting depensatory mortality. In nutritionally stressed populations, no correlation was found between biomass and ovipositional preference, but attractiveness of the water was significantly increased by the removal of individuals by pupation or mortality. Egg hatchability was not significantly affected by population structure, but varied with the nutrient content of the water. This study provides new insight into the use of parasites as agents in the biological control of mosquitoes.

No description available.

This study documents dynamic changes in the mean abundance and body size of arthropods in an ephemeral pond over the course of a summer in order to understand the nature of interactions that shape this community, and to assess the risks posed by exposure to cercariae of the entomopathogenic digenean, Plagiorchis elegans, a potential control agent for larval mosquitoes. Chironomids were the most abundant, comprising almost two-thirds of all arthropods collected; they were followed by chaoborids, the most abundant predator. Other arthropods, in decreasing order of abundance, were the ephemerids, isopods, amphipods, odonates, dytiscids, and hemipterans. Infections were found only in chironomids and were extremely rare and of low intensity, conceivably due to predation of chaoborids on cercariae and may have protected the community from exposure to these parasites. Findings are discussed in terms of using entomopathogenic digeneans as agents in the biological control of mosquitoes.

Estuaries are productive ecological transition zones between freshwater and marine environments that provide important commercial, recreational, aesthetic and cultural resources. The Avon-Heathcote estuary in Christchurch, New Zealand, is no exception, and its close proximity to different kāinga and Christchurch city has provided cultural, recreational and aesthetic values for centuries, especially Mahinga kai for Tangata Whenua. Tuangi (The New Zealand cockle, Austrovenus stutchuryi) is an important source of Mahinga kai to the iwi Ngai Tahu, but also an important ecological ecosystem engineer that provides internal habitat to parasites and, through its shell production, external habitat (hard substratum) for epibiota species. Several parasites, in particular the metacercariae echinostome parasite Curtuteria australis, depend on Austrovenus as its intermediate host, and these parasites can be considered allogenic engineers because they turn living material (here the host) from one physical state into a second. This is particularly evident in intertidal sedimentary estuaries where parasites, including Curtuteria, can alter the behaviour and fitness of the ecosystem-engineering hosts and thereby alter entire community structures. Similarly, several epibiota species depend on the shell of Austrovenus as a substratum on which to live. This hard substratum is particularly important for epibiota in estuaries that are devoid of rocky reefs, including autogenic ecosystem engineers like common large macroalgae (e.g. Ulva spp.). However, the Avon-Heathcote estuary, like many estuaries around the world, has become nutrient-enriched following sewage wastewater discharges, input from rivers and encroaching urban development, facilitating enhanced growth of algae attached to shells. Following recruitment and rapid growth on the shells, large algal fronds can break off and accumulate into thick mats that may cause anoxia and detrimental effects on many estuarine organisms. The main objective of this thesis is to quantify key linkages between three types of ecosystem engineers; the cockle Austrovenus, its internal parasites and its external epibiota community, including large macroalgae that can detach from the shell and develop into free-living mats. To address these objectives, spatial-temporal field surveys and laboratory and field experiments investigated (i) when and where Austrovenus provide internal habitat to parasites and external habitat to epibiota, and (ii) if and how parasites and epibiota affect survival and positioning of Austrovenus in or on the sediment. It was hypothesized that parasites and epibiota species would be abundant in and on Austrovenus and that their densities would vary across seasons and environmental gradients. It was also expected that parasites would reduce the ability of Austrovenus to bury themselves, so that surface-lying cockles would have higher parasite densities and be more susceptible to predation. Finally, it was hypothesized that a cover of macroalgae would decrease the susceptibility of Austrovenus to predation, but have negative effects on associated epibiota species, and that herbivorous epibiota species, through grazing, could control the abundance of epibiotic Ulva recruits. Seasonal collections of Austrovenus showed that parasite densities varied in different environments within the estuary (mean ranged from 3-129 for buried hosts and 7-187 for surface-selected hosts). However, host parasite loads did not vary between seasons. Parasite infestation was, found to be slightly higher in hosts exposed above the sediment compared to those buried in sediment. However, the test factor host position accounted for < 1% of the total data variability and therefore host position is of relative low ecological importance. Spatial variability in host parasite loads was significantly correlated to host sizes (its width, Rho = 0.72), individual epibiota species (Anthopleura and Elminius, Rho = –0.11 and Rho = 0.1, respectively), percentage coarse ssediment (Rho = 0.55), and less so to salinity (Rho = 0.42) and elevation level (Rho = 0.33), although the latter two variables were not statistically significant. A laboratory experiment did not confirm the expected hypothesis that hosts with high parasites loads had impaired burrowing ability. A 6-week field experiment, where the burrowing ability of the host was manipulated to increase its visibility, showed that hosts with reduced burrowing abilities did not have higher mortality than hosts with normal burring ability. Epibiota species were also highly variable in the estuary. A spatial survey from 15 sites found four encrusting and 11 solitary epibiota species with highly variable densities across sites and seasons. Factors that accounted for epibiota richness and density included host size and seasonality (particularly for macroalgal species), whereas environmental gradients and co-occurrence patterns with different epibiota species explained additional variability for only a few species. Foliose and tubular forms of Ulva spp. were the most abundant epibiota species throughout estuary (on average 2.3 and 1.7 per host, respectively) and were therefore studied in more detail. A 6-week field experiment showed that drift macroalgal mats had little effect on densities of either Austrovenus or epibiota species. Similarly, another field experiment showed that predators had no impact on Austrovenus abundances, irrespective of its size, if Austrovenus was allowed to bury or not, and if it was unconcealed or concealed under macroalgal mats. Finally, a laboratory experiment showed that small meso-grazers, under natural background densities, could not reduce densities or sizes of Ulva recruits on shells or barnacles (attached to Austrovenus shells). This study has shown that a single species of estuarine shell-forming ecosystem engineer provides ubiquitous internal and external habitat for other species throughout an estuary. The study has helped clarify how ecosystem engineers can directly control species abundances (here of parasites and epibiota) but also function as nursery grounds for other important ecosystem engineers (here bloom-forming drift algae). Furthermore, and in contrast to past research, this study did not find strong relationships between parasites and Austrovenus or its epibiota, suggesting that past generalisations about parasite effects may not be applicable within and between all estuaries. Finally, the study documented that drift macroalgae and consumers, in natural background densities, had very little impact on Austrovenus and its epibiota. Previous studies have shown that hosts with high parasite loads are commonly found on the sediment surface. These studies have suggested that this impaired burial ability makes the host more vulnerable to predation (by the parasites final host). However, at the same time, surface-lying host are also more exposed to fouling by epibiota species, which could reduce predation (by the final host) because epibiota may conceal it. However, this thesis found little support for either of these opposing ecological processes; parasite loads did not decrease burial ability, and host exposed the surface were not predated more, irrespective of being concealed or not Clearly, future studies should aim to identify thresholds in space, time, and densities where parasites, macroalgae and consumers have stronger impacts on Austrovenus and each other than shown here.