Dissertations / Theses on the topic 'Freshwater biology'

Freshwater planarian Schmidtea mediterranea is an emerging model for studying in vivo gene functions and regulation in native cell niches. The obligate asexual strain of this species reproduces by fission, in which succession of soma occurs without passing through the germline. To achieve this somatic immortality the somatic stem cells need to overcome the end replication problem. Therefore it can be hypothesised that somatic telomere maintenance in asexual S. mediterranea must possess a germ-like property, with which age-related erosions can be adequately repaired. In this PhD project, the telomere repeat unit in S. mediterranea was confirmed to be the vertebrate-like TTAGGG. Attrition of whole body telomere length was found in ageing sexual worms and also in asexual worms which had not gone through recent fission events. Opposite telomere length dynamics were observed in regenerated samples of the two strains, with erosion in the sexuals and reset in the asexuals. The telomere maintenance was found to increase during regeneration in both strains, with a higher level of increase in asexual worms. A homolog of the telomerase reverse transcriptase subunit, Smed_Tert, was identified and characterised in this organism. High level of Smed_Tert expression was seen in germ cells in mature sexual worms and adult stem cells in asexual worms. Knockdown of Smed_Tert expression by RNA interference caused progressive telomere erosion, however effects on cell proliferation and viability have not been observed in knockdown samples. Four alternate splice isoforms of Smed_Tert were identified. The enhanced telomerase activity during regeneration correlates with a proportional increase in the full-length isoform and a decrease in isoforms with a truncated TRBD domain, suggesting a dominant negative regulation of telomerase by alternative splicing. Significant increase in the expression of the full-length isoform was seen in regenerating asexual samples but not in sexual strains, which correlates with their telomere length dynamics. It is hoped that the comparative studies between the sexual and asexual strains can improve our understanding of how soma can evolve to become an effective inheritable unit.

Abstract

The sediment requirements for freshwater pearl mussel (Margaritifera margaritifera) recruitment, in 18 rivers in the counties of Västra Götaland, Örebro, Värmland and Västmanland in Sweden, were investigated. The top 4 cm of sediment in the rivers was analysed in terms of size, distribution and organic compound within the fine sediment. The aims of the study were to determine whether there is a relation between sediment particle size compound and freshwater pearl mussel recruitment as well as between organic compound in fine sediment and recruitment of mussels. The study shows that there is a significant difference in the amount of organic silt between non-recruitment and recruitment sites with a higher percentage of organic silt in recruitment sites. There is also a legible difference between the amounts of silt per sample between non-recruitment sites and recruitment sites where there was significantly more silt in sediment samples of non-recruitment sites. With the exception of fine sediment, no significant difference was found between non-recruitment and recruitment sites regarding size class distribution.

Sammanfattning

Sedimentkraven för rekrytering hos flodpärlmussla (Margaritifera maragaritifera) i 18 svenska vattendrag belägna i Västra Götalands, Örebro, Värmlands och Västmanlands län undersöktes. Vattendragens översta 4 cm sediment analyserades gällande storlek, fördelning och organisk sammansättning i finsedimentet. Målen med studien var att fastställa huruvida det finns förhållanden mellan sedimentets partikelstorleksammansättning och rekrytering av flodpärlmussla samt mellan finsedimentets organiska sammansättning och rekrytering av musslor. Studien visar en signifikant skillnad i organiskt finsediment mellan icke-rekryteringsplatser och platser med rekrytering där rekryteringsplatser hade högre procentuell andel organiskt finsediment. En signifikant skillnad påvisades också mellan andel finsediment per sedimentprov där sedimentprov från icke-rekryteringsplatser innehöll en högre procentuell andel finsediment. Förutom gällande finsediment påvisades ingen signifikant skillnad i sedimentets storleksdistribution mellan rekryterings- och icke-rekryteringsplatser.

Biology
Ph.D.
Environmental heterogeneity in both space and time has significant repercussions for community structure and ecosystem processes. Dimictic lakes provide examples of vertically structured ecosystems that oscillate between stable and mixed thermal layers on a seasonal basis. Vertical patterns in abiotic conditions vary during both states, but with differing degrees of variation. For example, during summer thermal stratification there is high spatial heterogeneity in temperature, nutrients, dissolved oxygen and photosynthetically active radiation. The breakdown of stratification and subsequent mixing of the water column in fall greatly reduces the stability of the water column to a vertical gradient in light. Nutrients and biomass that were otherwise constrained to the depths are also suspended, leading to a boom in productivity. Freshwater lakes are teeming with microbial diversity that responds to the dynamic environment in a seemingly predictable manner. Although such patterns have been well studied for nanoplanktonic phototrophic and heterotrophic populations, less work has been done to integrate the influence of mixotrophic nutrition to the protistan assemblage. Phagotrophy by phytoplankton increases the complexity of nutrient and energy flow due to their dual functioning as producers and consumers. The role of mixotrophs in freshwater planktonic communities also varies depending on the relative balance between taxon-specific utilization of carbon and energy sources that ranges widely between phototrophy and heterotrophy. Therefore, the role of mixotrophy in the microbial food web is difficult to predict because functional types of mixotrophs along a gradient of nutritional strategies contribute differently to nutrient cycling and carbon sequestration. The overall objective of this work was to advance existing knowledge of the abundance and activity of phagotrophy phytoplankton in lacustrine systems. The incorporation of mixotrophy into the microbial food web requires the complement of physiological studies in culture (as described in chapter 2) and quantification of activity (including abundance and bacterivory) in relation to strict phototrophs and heterotrophs in situ (as described in chapter 3 and 4). Information on the physiological ecology of mixotrophic protists is crucial to understanding their role in planktonic food webs and influence on the dynamic microbial community structure in lake ecosystems. An understanding of the ecological functioning of lakes has ultimate consequences for management of water resources, particularly in the face of global climate change.
Temple University--Theses

Storvuxna musslor i sötvatten (stormusslor) kan ha drabbats av en allvarlig tillbakagång i såväl Sverige som hela världen. Tidigare undersökningar i Sverige och andra delar av världen visar på en kraftig tillbakagång och brist på en fungerande föryngring hos arterna flodpärlmussla (Margaritifera margaritifera) och tjockskalig målarmussla (Unio crassus). I tidigare undersökningar i Sverige har fokus främst varit att försöka kartera arternas förekomst och utbredning, men inte dess föryngring. Syftet med denna studie är att undersöka föryngringen av samtliga arter stormusslor i vattensystemen Tidan, Lidan och Mariedalsån i Västra Götalands län. Sju lokaler valdes selektivt ut för att representera några av de bästa i de tre vattensystemen. Inventeringen utfördes främst med vattenkikare men även med luther- räfsa. Sedimentprov utfördes i lokalerna för undersökning av juvenila musslor. Musslorna räknades, artbestämdes, mättes och åldersbestämdes utifrån räknade vinterringar på skalen. Resultatet i studien pekar på att föryngringen är mycket dålig i flertalet lokaler även hos vanligt förekommande arter i landet som allmän dammussla (Anodonta anatina) och spetsig målarmussla (Unio tumidus). Förekomsten av arter stormusslor i lokalerna är dålig och tyder på relativt artfattiga vatten i Tidan, Lidan och Mariedalsån. Då de inventerade lokalerna ska representera några av de bästa i de tre vattensystemen är resultaten på föryngringen i vattendragen mycket oroväckande. Fortsatta studier bör göras på föryngringen i vattendragen för samtliga arter stormusslor i Västra Götalands län, nationellt och internationellt.

Freshwater mussels (Unionoida) may have been substantially reduced in Sweden as well as the whole world. Earlier studies show that the species Margaritifera margaritifera and Unio crassus has been substantially reduced and there are several localities with no reproduction in Sweden and in several other parts of the world. Other species of freshwater mussels in Sweden have not been studied very much and the focus of studies in Sweden has been on the species existence, not their reproduction. The purpose with this study is to examine the existence of reproduction of different kind of freshwater mussels in the water systems Tidan, Lidan and Mariedalsån in Sweden. Seven localities were choosing selective for the study to represent some of the best localities in the water systems. The freshwater mussels were studied on the bottom and in the sediment. The lengths of mussels were measured and the winter rings were counted to estimate the age of the mussels. The result of this study point on a very bad reproduction in several localities even with the most common species in Sweden and the diversity of species are low in the water systems Tidan, Lidan and Mariedalsån. These localities were supposed to represent some of the best localities in the water systems and because of that the result of the bad reproduction is very concerning. More studies of the reproduction of freshwater mussels even the more common species is recommended in Sweden and other countries of the world.

The number of species extinctions is increasing at an alarming rate. Long-lived freshwater mussels of the order Unionoida, which include a parasitic stage on a host fish, are highly threatened. Habitat degradation by turbidity and sedimentation is thought to be one major reason for their decline. The objective of this thesis was to examine recruitment patterns and identify the causes of the lack of recruitment in the threatened unionoid freshwater pearl mussel (Margaritifera margaritifera). In addition, I investigated the effects of turbidity on non-endangered dreissenid mussels, where turbidity was manipulated through use of bioturbating mayflies.

In a survey of 107 Swedish streams, mussel population size and trout density were both positively correlated to recruitment probability of M. margaritifera. A more in-depth study of the age-structure of nine populations revealed that four of these populations showed no signs of recruitment over the last ten years. Within-stream variation in recruitment was high as both mussels and trout had patchy distribution, and may be important for population regulation. Moreover, examination of different life stages revealed no differences in the gravid mussel stage or the stage when mussels infect salmonid fish. Instead, differences were observed for the juvenile, benthic stage, presumably related to differences in turbidity and sedimentation. High turbidity may affect filter-feeding efficiency of mussels and high sedimentation may reduce survival by clogging sediments, thereby altering, for example, oxygen and food conditions. In the study of the effects of turbidity, bioturbating mayflies increased turbidity and filter-feeding dreissenid mussels reduced turbidity. Mussel growth both decreased and increased with increasing turbidity, depending on sediment type.

Turbidity and sedimentation often impact entire stream systems, and a holistic, catchment-based management strategy may be needed to reduce the effects of sedimentation on freshwater pearl mussels. The effects of restoration take a long time and must start soon if recruitment of mussels is to be re-established. Restoration may also be more urgent in some streams than in others, as the maximum age of M. margaritifera populations in my study differed by as much as 60 years. As mussel and trout densities seem to be important for recruitment success, one conservation method may be to concentrate mussels into sites where trout density is high.

Mechano-sensitive ion channels in cells isolated from the heart and circumoesophageal ganglia of a freshwater snail (Lymnaea stagnalis) were characterized as K$\sp+$ selective and sensitive to changes in cell membrane tension. Using the technique of single-channel recording, stretch-activated K$\sp+$ (SAK) channels (30 pS in physiological saline) were shown to have complex permeation properties indicative of multi-ion channels. SAK channels were blocked by milli-molar quantities of quinidine or tetraethyl-ammonium and exhibited selectivity (Tl$\sp+ >$ K$\sp+ >$ Rb$\sp+ >$ Na$\sp+ >$ Li$\sp+$) properties seen in many other K$\sp+$ channels. SAK channels described in Lymnaea ventricular cells or neuron somas and growth cones were activated (increased open probability, P$\sb{\rm o}$) by increases in membrane tension produced by suction on the cell membrane. Stretch-activation was a reversible and repeatable phenomenon, associated with a reduction in a long closed time separating bursts of openings, rather than by an increase in the open time. The SAK channel's stretch-sensitivity was variable between patches, a finding attributable to the inability to accurately determine membrane tension. In spite of this, kinetic analysis of heart SAK channels established the presence of at least two open and three closed states. Similar analysis of neuron SAK channels indicated at least two open and four closed states. In channels from both cell types, only the long closed time constant ($\tau\sb{\rm C4}$, extracted from closed time frequency distributions) showed sufficient mechano-sensitivity to produce the observed increase in P$\sb{\rm o}$ with increasing membrane tension (in one patch, when P$\sb{\rm o}$ increased by a factor of 77 times the zero pressure P$\sb{\rm o}$, $\tau\sb{\rm C4}$ decreased by a factor of 22). In spite of the absence of specific SAK channel antagonists, attempts were made to establish a physiological role for SAK channels. Neurons and heart cells were shown to be resistant to severe hyposmotic insults. Hyposmotic shock resulted in hyperpolarization of the neuron soma resting potential and activation of SAK channels. These results suggested that SAK channels may contribute to osmotic-swelling limitation. SAK channels were found in developing neuron growth cones as well as the cell body. Channel characteristics were similar in both structures and circumstantial evidence points to expression of new SAK channels during neurite development. A new type of mechano-sensitive K$\sp+$ channel was found to coexist with SAK channels in neuron cell bodies and growth cones. These channels were in-activated (SIK) by increases in membrane tension and possessed a greater stretch-sensitivity than SAK channels. Decreased P$\sb{\rm o}$ was found to result from the lengthening of the long closed time in a fashion analogous but opposite to that seen in SAK channels, thus implying a common transduction mechanism. The differing stretch-sensitivities combined with similar permeation properties (6.6 pS in physiological saline; selectivity sequence, Tl$\sp+ >$ K$\sp+ >$ Rb$\sp+ >$ Na$\sp+$) suggested that membrane tension could control cell resting potential and thus modulate voltage-activated Ca$\sp{2+}$ channels and therefore the influx of Ca$\sp{2+}$, a known regulatory ion. SIK and SAK channels could therefore provide a mechanism for linking Ca$\sp{2+}$ influx to tension during axonal outgrowth.

Tidal freshwater wetlands represent a transitional wetland between tidal salt marshes and non-tidal wetlands. as such, they exhibit some of the vegetation characteristics of both systems. If the changes in the vegetation pattern favor the characteristics of one system over the other, the changes may be an indication of changes in the environmental conditions of the estuarine ecosystem that favors that system. Unfortunately, little is known of the temporal and spatial changes that occur in the vegetation patterns of tidal freshwater marshes of the mid-Atlantic coastal region. In 1987 a vegetation analysis was done on a 60 hectare section of Sweet Hall Marsh, a tidal freshwater marsh of Chesapeake Bay. The data was compared with that of a similar study completed in 1974 to determine the changes that may have occurred in the vegetation pattern of the marsh. The results found that there was no significant difference in the species diversity of the two studies. However, further analysis showed that there was a change in the plant species contributing to the diversity. Spartina cynosuroides, an oligohaline species that was not important in the 1974 study, had the fourth highest importance value in this study. The shift in species composition of Sweet Hall Marsh may reflect a shift in the marsh's environment from being historically that of tidal fresh water to one of being more transitional between oligohaline and tidal fresh water.

The sources and fates of carbon in a tidal freshwater marsh (Sweet Hall marsh; Pamunkey River, Virginia) were determined to understand the role that these marshes play with respect to estuarine carbon cycling. A carbon gas flux model, based on measured carbon dioxide and methane fluxes, was developed to calculate annual rates of macrophyte and microalgal photosynthesis and community and belowground respiration. Because carbon fluxes out of marsh sediments may underestimate true belowground respiration if sediment-produced gases are transported through plant tissues, gross nitrogen mineralization was used as a proxy for belowground carbon respiration. Annual community respiration exceeded gross photosynthesis, suggesting an allochthonous input of organic carbon to the marsh. Sediment deposition during tidal flooding was measured as a potential exogenous carbon source. Short term deposition rates (biweekly to monthly) were spatially and temporally variable, with highest rates measured near a tidal creek during summer. Annual deposition on the marsh was sufficient to balance relative sea level rise and measured respiration rates. Sediment inventories of 7Be indicated that spatial patterns of sedimentation were not due to sediment redistribution within the marsh. Accretion rates calculated from 137Cs (decadal scale) and 14C (centuries to millennia) were substantially less than annual deposition rates. The concentration and isotopic composition of dissolved and particulate inorganic and organic carbon (DIC, DOC, POC) were measured in a marsh creek which drained the study site. Seasonal isotopic variations in DIC were explained by marsh porewater drainage and decomposition of marsh-derived carbon. A model linking DIC concentrations and water transport showed that DIC export from tidal marshes could explain a significant portion of excess DIC production in the adjacent estuary. Isotopic mixing models indicated seasonal variability in the importance of phytoplankton as a source of DOC and POC although there was no evidence for a net flux of these materials between the marsh and estuary. Annually, the marsh carbon budget was closely balanced, with sources exceeding sinks by approximately 5 percent. This similarity suggests that those processes which were not quantified (e.g. consumption by marsh and riverine fauna) were quantitatively unimportant with respect to the entire marsh carbon budget.

Abstract

This study takes up a local issue in the village of Lekhyttan, where Johan Molin is concerned about the freshwater pearl mussels (Margaritifera margaritifera) situation. He is a landowner and wonders what the situation is for the mussels and what he himself possibly can do, to hopefully improve their situation.

This paper looks at the different aspects on why the mussels are distributed as they are in the stream and trying to understand why new recruitment is poor in the Lekhyttan Stream.

Dividing the area into two zones, east (that has a population of mussels) and west (which has none), makes it easier to analyse which type of habitat they prefer. Why the mussels can be found in one zone and not in the other can be due to several different factors.

The factors investigated were: 1) bottom structure, 2) trout (Salmo trutta) - spawning area and mature trout habitat as the trout play an important role in the mussels lifecycle,

3) surrounding vegetation, 4) predation from signal crayfish (Pacifastacus leniusculus) and 5) water quality checked with a pH and iron test – from the inflows of ditches and pipes.

There was a significant difference between the two zones in the bottom sediment structure: the west zone had a high percentage of stone, whilst the east zone consisted of finer materials and had far more suitable habitat areas for the trout (both in spawning as well as for larger trout). Tests from the inflowing water in the west zone had water with low and high pH levels, as well as high iron contents. These inflows need to be fixed with a pond and reed filtration bed, as well as a recommendation on cutting back the number of crayfish that can be a potential threat to juvenile mussels. Following these recommendations will hopefully improve the situation locally for the Lekhyttan freshwater pearl mussel and maybe even lead to new recruitment.

Herbivory is thought to be nutritionally inefficient relative to carnivory and omnivory. But, herbivory evolved from carnivory in many lineages, suggesting that there are advantages to eating plants. To understand the adaptive significance of the transition from carnivory to herbivory, I proposed five hypotheses for the adaptive evolution of herbivory and reviewed the current freshwater literature to identify conditions where eating plants might be adaptive over eating animals. I tested three of these ideas (Suboptimal Habitat, Heterotroph Facilitation, and Lipid Allocation) using the herbivorous Sailfin Molly (Poecilia latipinna)and identified each as a potential mechanism for the evolution of herbivory. To understand the origins of herbivory in Sailfin Mollies, I reconstructed ancestral habitats and dietsacross a phylogeny of the genus Poeciliaand then used phylogenetically independent contrasts to identify patterns of diet evolution. I found that the degree of herbivory increases with increasing salinity affiliation, suggesting that in this genus, herbivory evolved as an adaptation for invading less productive saline habitats from freshwaters. This result is consistent with the Suboptimal Habitat hypothesis, which states that herbivory allows organisms to invade and persist in ‘suboptimal’ habitats. To understand how herbivory is maintained in extant populations, I raised juvenile Sailfin Mollies in mesocosms and enclosure cages placed in the Everglades to document that dietary autotrophic lipids play a role in early life history by supporting rapid growth (Lipid Allocation). However, dietary bacterial fatty acids promoted fish survival, consistent with the Heterotroph Facilitation hypothesis, which states that indirect detritivory supplements the herbivorous diet. Finally, I quantified periphyton quality/availability and consumer density across the Everglades landscape to examine the correlates of trophic dynamics in nature. Results revealed that herbivores can persist in diverse habitats and survive on varying resources when habitats are unfavorable, supporting the Suboptimal Habitat hypothesis.

This thesis examines the branchial mechanisms utilized by freshwater fish to regulate internal acid-base status and presents a model to explain the underlying basis of the compensatory processes. Rainbow trout, Oncorhynchus mykiss, brown bullhead, Ictalurus nebulosus, and American eels, Anguilla rostrata, were examined under a variety of experimental treatments which induced both respiratory (hyperoxia, hypercapnia) and metabolic (post-hyperoxia, post-hypercapnia, HCl infusion, NaHCO$\sb3$ infusion) acid-base disturbances. Acid-base-regulation was achieved by appropriate adjustments of Na$\sp+$ and Cl$\sp-$ net fluxes across the gills which, in turn, were accomplished by variable contributions of three different branchial mechanisms; (i) morphological adjustments to the gill epithelium, (ii) changes in internal (H$\sp+,$ HCO$\sb3\sp-)$ and external (Na$\sp+,$ HCO$\sb3\sp-)$ substrate availability, and (iii) differential changes in Na$\sp+$ versus Cl$\sp-$ net fluxes through regulation of Cl$\sp-$ efflux. This thesis determined the variable contribution of each of these mechanisms to overall compensation of acid-base disturbances. In brown bullhead and trout, respiratory acidosis caused a reduction in chloride cell (CC) surface area whereas alkalosis was associated with increases in CC surface area. Increases in the density of microvilli displayed on the external surface of the PVC coupled with ultrastructural modifications during hypercapnic acidosis were associated with increases in Na$\sp+$ uptake $\rm(J\sb{in}\sp{Na+}).$ In addition to the effect that alterations in CC surface area have on the rate of Cl$\sp-$/HCO$\sb3\sp-$ exchange $\rm(J\sb{in}\sp{Cl-}),$ it was demonstrated that changes in the concentration of the internal counter-ion (HCO$\sb3\sp-)$ may alter the rates of acid-base compensation. When (HCO$\sb3\sp-$) is elevated, $\rm J\sb{max}\sp{Cl-}$ is elevated thereby increasing the capacity to excrete HCO$\sb3\sp-$ via the Cl$\sp-$/HCO$\sb3\sp-$ exchanger over and above those determined by CC morphology. This is an important mechanism to increase the rate of acid-base compensation during metabolic alkalosis. (Abstract shortened by UMI.)

The freshwater shrimp Hemimysis anomala is a recent Ponto-Caspian invader of the Great Lakes – St. Lawrence River basin. Based on its invasion history, high predation rate and the naiveté of the ecosystems in which it has been introduced, it has the potential to exert strong impacts on native food webs. Risk assessment and effective monitoring of the spread of this invader require information about the environmental factors that limit its local abundance and distribution. A literature review suggests that H. anomala has broad environmental tolerances but may be limited by low water conductivity levels, high local flow, and low dissolved oxygen. An empirical model derived from results of a field study in the St. Lawrence River identified specific conductivity and shoreline heterogeneity as important predictors of H. anomala occurrence and abundance across sites. The relationship between conductivity and H. anomala occurrence is further supported by experimental evidence that demonstrates lower functional responses at lower conductivity levels. Distance from shore and depth were also good predictors of H. anomala abundance, which was maximal in areas close to shore and at depths above 2 m.
La crevette d'eau douce Hemimysis anomala est une espèce envahissante provenant de la région Ponto-Caspienne qui a été découverte récemment dans le bassin des Grands Lacs et du fleuve Saint-Laurent. En raison de ses fortes tendances envahissantes, de son taux de prédation élevé et de la naïveté des écosystèmes dans lesquels elle a été introduite, elle pourrait avoir des impacts considérables sur les réseaux alimentaires locaux. Afin d'évaluer les risques et de surveiller de manière efficace la dispersion de cette espèce, point est besoin d'avoir accès à de l'information sur les facteurs environnementaux qui limitent son abondance locale et sa distribution. Une recension de la littérature suggère que H. anomala fait preuve de tolérance environnementale, mais qu'une basse conductivité d'eau, de hauts courants locaux et une basse concentration d'oxygène dissous peuvent diminuer cette tolérance. Un modèle empirique, mis au point à partir des résultats d'une étude de terrain menée dans le fleuve Saint-Laurent, démontre que la conductivité spécifique et l'hétérogénéité du rivage constituent des facteurs de prédiction de la présence et de l'abondance de H. anomala à travers les sites. La relation entre la conductivité de l'eau et la présence de H. anomala est, en outre, soutenue par des preuves expérimentales qui mettent en exergue une réponse fonctionnelle réduite à de bas niveaux de conductivité. La distance du rivage et la profondeur sont aussi de bons indices d'abondance de H. anomala; la concentration de crevettes atteint d'ailleurs son point le plus haut près du rivage et à plus de deux mètres de profondeur.

The two papers presented in this thesis focus on population genetic study on freshwater pearl mussel populations in Sweden, using RAPD method. In paper I, I examine genetic variation within and between 5 populations in a single drainage area in south western Sweden. In paper II, I study the evolutionary relationship, and how genetic variation is related to population size, age structure and geographic isolation in 14 populations of freshwater pearl mussel in south central Sweden. In both papers I and II, I found that genetic variation was larger than found in previous studies using other techniques, and variation was larger between than within populations. I did not found any correlation between geographic and genetic distance, which indicates that mussel populations have been adapted locally to environmental factors in a relatively short time. In paper I, I found that genetic distance between populations was greater than found in other studies, despite small geographic distances. In paper II, I found that populations were highly differentiated indicating little gene flow between them. There was no significant positive relation between genetic variation and population size or age structure but there was a significant positive relation between mean age and population size indicating that many populations have gone through bottlenecks recently.

This study is concerned with two strigeid genera which utilise fish as their second intermediate host and piscivorous birds as a definitive host, i.e. Apatemon (Apatemon) Sudarikov, 1959 and Ichthyocotylurus Odening, 1969. Although the lifecycle has been ascertained for most Ichthyocotylurus spp., confusion and disagreement still exist as to the constituent species, while all of the life-stages have been described for only a single member of the subgenus Apatemon (Apatemon). In order to clarify species membership to these taxa and indeed the taxonomic position of the subgenus Apatemon (Apatemon) further information was required on the life-cycles and life-stages of these strigeids. Although, metacercariae from this family have been recorded from a variety of British fishes, confirmed records, i.e. those supported with life-cycle data, are limited to a single species. It was this lack of confidence in identifying metacercariae recovered from fishes and the lack of known good criteria for distinguishing the adults that prompted the present study. Collections of metacercariae from a variety of hosts and locations were made, from which all subsequent life-cycle stages were obtained. The project aims were to establish the identity of the forms occurring in British fishes, by applying discriminatory techniques to the experimentally reared life-stages. In addition to traditional methods, techniques with little previous application to these genera were used and included, scanning electron microscopy (SEM), chaetotaxy, principal components analysis (PCA), and karyology. Furthermore, behavioural aspects such as the release patterns of cercariae from their molluscan hosts were studied to investigate whether they would prove to be of diagnostic value. Metacercariae obtained from the sampling survey were tentatively identified, using all currently employed methods for their determination, i.e. morphology, nature of cyst, host and site specificities, as Ichthyocotylurus erraticus (Rudolphi, 1809), I. variegatus (Creplin, 1825), Apatemon gracilis (Rudolphi, 1819) and A. annuligerum (Nordmann, 1832). Material collected from Finland was considered to contain both Ichthyocotylurus spp. recovered in the U.K., as well as I. platycephalus (Creplin, 1825) and I. pileatus (Rudolphi, 1802). The Ichthyocotylurus spp. were found to be more host specific than A. gracilis, although A. annuligerum was considered oioxenic to perch Perea fluiatilis L. Records of I. erraticus from gwyniad Coregonus lavaretus (L.) and grayling Thymallus thymallus (L.), and A. gracilis from arctic charr Salvelinus alpinus (L.) constitute first listings from Britain. The large number of sensilla present on the body surface of these metacercariae, observed by SEM and chaetotaxy, precluded their diagnostic use. PCA was, however, found to be of value for distinguishing between species and determining morphological variation within a species. I. erraticus, I. variegatus and A. gracilis adults were successfully reared in experimental hosts using metacercariae from a variety of fish hosts, sites within a single fish host and geographical sites. The adults obtained enabled clarification of the identities assigned to the metacercariae. Those metacercariae believed to represent I. pileatus and A. annuligerum failed to establish in experimental hosts. Herring gulls and lesser black-backed gulls proved to be extremely good experimental hosts for both Ichthyocotylurus spp., with the vast majority of infections establishing and providing high yields of eggs and adults. These infections yielded information on the establishment, development, fecundity, site specificity, longevity and morphological variability of the adults. Aspects of the morphology and biology of I. variegatus adults recorded were found to support its validity as a species discrete from I. platycephalus which was in some doubt. The experimental hosts used for A. gracilis infections, domestic and mallard ducklings, were found to be less satisfactory. Challenges were performed with A. gracilis metacercariae from three sources, rainbow trout, salmon parr and stone loach. The latter source was the only one to result in egg producing adults, with specimens exhibiting normal morphology and demonstrating an increased longevity over adults raised from salmonid metacercariae. These findings suggest that the metacercarial host may affect the successful completion of the life-cycle. Eggs of known origin were collected for all three cultured strigeid species, enabling further life-cycle studies, these were incubated and miracidia successfully raised. Developmental periods were found to be temperature dependent and differed for the three species at 20°C: A. gracilis < I. erraticus < I. variegatus. Light microscopy revealed the morphology of all three species to be identical, as were the epidermal plate formulae and chaetotaxy, indicated by silver-staining. The nomenclature for the distribution of miracidial sensilla derived by Dimitrov et al. (1989) was amended to enable a full description of these species. Osmotic shock resulted in an improved deciliation of the miracidia compared to sonication and subsequent SEM observation confirmed the arrangement of body surface structures, while revealing sensilla forms. Behavioural aspects of I. variegatus miracidia were examined, with a maximum longevity (< 11 hours) recorded at the lowest temperature studied (l0 degrees C), and host finding demonstrated to occur by an increased turning response in the presence of substances emitted from the susceptible snail host, following an initial unresponsive dispersal phase. Ichthyocotylurus cercariae were found in naturally infected Valvata piscinalis which constitutes the first record in Britain of cercariae of this genus. Cercariae of I. erraticus and I. variegatus were successfully raised experimentally from miracidia of known identity and origin within naive, experimentally raised V. piscinalis hosts, while A. gracilis cercariae were obtained from laboratory reared Lymnaea peregra. Cercarial developmental periods within the molluscan host were found to be temperature dependent and markedly different for the strigeid genera investigated, as were their behaviour and morphology. The Ichthyocotylurus spp. exhibit a distinct diurnal emergence rhythm from their molluscan host, being shed during the hours of daylight, while A. gracilis cercariae demonstrate a reciprocal pattern, emerging during the hours of darkness. Behavioural contrasts were also observed in longevities, emergence strategies (route of exit) and swimming behaviour. The two Ichthyocotylurus spp. were extremely similar, the only cercarial features found to be of diagnostic use were: the presence or absence of eye-spots; their differing developmental periods from miracidium to cercaria; the number and distribution of sensilla when compared by PCA; and their differing longevities at 20 degrees C. Characters considered to be of value in differentiating between strigeid cercariae at the species level, including the armature, chaetotaxy pattern and resting posture, did not differ between these two species. SEM observations enabled descriptions of the variety and structure of sensilla present on different life-stages, while transmission electron microscopy revealed the internal structure of cercarial sensory structures. Experimentally raised cercariae were found to be infective and the life-cycle was completed for the three strigeid species. Host specificities were observed for I. erraticus and A. gracilis, being particularly stringent for the latter species, while site specificities recorded were as observed in natural infections. Metacercarial maturation periods (for encystment) were highly temperature dependent, being comparable for the two Ichthyocotylurus spp. and more rapid than for A. gracilis specimens.

During the Late Woodland Period in the American Southeast, the amount of space that any individual group could exploit began to shrink, due to the presence of other groups on the landscape. Resource expansion occurred to augment food supplies, resulting in increased exploitation of mussel beds. Because mussels can be extremely sensitive to the characteristics of the waterways they live in, the specific habitat requirements of these animals can be used to reconstruct the environments they were recovered from. In this thesis I use freshwater mussel assemblages to reconstruct hypothetical aquatic catchments and map them onto modern rivers in the Yazoo River Basin and the Tombigbee River Basin. These are used to test ethnographic models of exploited space. I also use detrended correspondence analysis to test if sites exist in mathematical space like they do in physical space along the Yazoo River basin, as observed in the Tombigbee River basin.

Although predation is the major factor responsible for nest losses in birds, predation patterns in marshes and adjacent uplands are poorly known. This study examined the factors affecting nest predation on marsh-nesting birds found in areas affected by different intensities of human disturbance (urban, agricultural, natural). Artificial nests simulating waterfowl and passerine nests were used for that purpose. The nests, located along transects running from the center of the marshes to the adjacent upland habitats, were set up in the months of May, June and July 1989 and 1990. Eggshell remains were used to identify the predators. Predation was higher on passerine than on waterfowl nests and on nests located in upland habitats. Deep water prevented mammalian predators from foraging deep in the marsh. Predation rates in urban and natural areas were high while nests located in agricultural areas suffered lower predation. Nest camouflage was generally unimportant in reducing chances of predation. Mammals were responsible for most of the predation events. Differences in density and/or diversity of predators in urban, agricultural and natural areas were the main causes of different predation patterns observed in the three areas.

This thesis addresses the idea that colony formation effectively increases the size of a phytoplankter thereby reducing grazing losses by deterring ingestion by zooplankton. It was initially hypothesized that colonies of Dinobryon (Ochromonadales, Chrysophyceae) deter zooplankton grazers, and that their spring population declined either because of a drop in the mean colony size of the Dinobryon population or from an increase in the abundances of large zooplankton grazers capable of ingesting large colonies. From January to May 1983 a small dystrophic lake was sampled weekly at three discrete depths at two stations. In the samples collected from one station, two species of Dinobryon, D. cylindricum Imhof and D. diverqens Imhof, as well as all zooplankton species were enumerated and morphometric variables of Dinobryon colonies were measured. The results showed that, alone, each of the original hypotheses could not account for the population and colony size dynamics of the Dinobryon species present in the lake. A new hypothesis was generated from the results which suggested that Dinobryon colonies minimized grazing losses to small grazers because of increased size and to larger grazers by fragmentation upon capture. Subsequent evaluation of the assumptions of this new hypothesis, using both the original data and new data from the second station, added further support to the hypothesis.
Science, Faculty of
Botany, Department of
Graduate

This thesis examines the production and distribution of dissolved gaseous mercury (DGM) in freshwater ecosystems and its relationship to mercury volatilization. The importance of volatilization was assessed within a multidisciplinary mercury mass balance for Big Dam West Lake (BDW) Kejimkujik Park, Nova Scotia. The magnitude of volatilization was found to be approximately double the direct wet deposition over lake and wetlands, and 27% of the direct wet deposition to the terrestrial catchment. Over the entire basin area the mass of mercury volatilized is 46% of the mass deposited by wet deposition. A new method of continuous (5 minute) DGM analysis was developed and tested. The detection limit for DGM was 20 fmol L-1 with 99% removal efficiency. Control experiments showed that there was no interference due to methyl mercury, which is present in similar concentrations to DGM. Experiments comparing continuous DGM analysis with discrete DGM analysis showed that the results are not significantly affected by typical variations in water temperature (4--30°C), oxidation-reduction potential (135--355 mV), dissolved organic carbon (4.5--10.5 mg L-1), or pH (3.5--7.8). The continuous analysis was within 4.5% of the discrete analysis when compared across 12 samples analyzed in triplicate. Diurnal patterns for dissolved gaseous mercury (DGM) and mercury flux were measured (using this new DGM method and a Teflon flux chamber method) in two lakes with contrasting dissolved organic carbon (DOC) concentrations in Kejimkujik Park, Nova Scotia. Consistently higher DGM concentrations were found in the high DOC lake as compared to the low DOC lake. Cross-correlation analysis indicated that DGM dynamics changed in response to solar radiation with lag-times of 65 and 90 minutes. An examination of current mercury flux models using this quantitative data indicated some good correlations between the data and predicted flux (r ranging from 0.27 to 0.83) but generally poor fit (standard deviation of residuals ranging from 0.97 to 3.38). This research indicates that DOC and wind speed may play important roles in DGM and mercury flux dynamics that have not been adequately accounted for in current predictive models. The distribution of DGM in the water columns of shallow and deep freshwater lakes was investigated in Lake Ontario and several small freshwater lakes. When DGM concentrations were expressed on an areal basis, DGM concentrations above the thermocline in Lake Ontario average 1.5 ng m-2 and in small freshwater lakes it ranged between 0.1 and 0.8 ng m -2. Further, it was demonstrated that the majority of DGM in large freshwater lakes such as Lake Ontario exists below the thermocline where photochemical oxidation and reduction processes cannot occur. The depth profiles indicate that vertical mixing in the water column may alter the DGM concentration in the upper epilimnion, and that turn over in deep lakes may result in a transfer of large concentrations of DGM from the hypolimnion into the epilimnion. In addition, the results indicate that microbial processes may be an important factor regulating DGM in the water column of freshwater lakes, particularly in the hypolimnion. (Abstract shortened by UMI.)

Prophenoloxidase (proPO) is a key enzyme for generation of melanin and is activated by the proPO activating enzyme (ppA) to its active form, PO. The active ppA was purified and cloned from crayfish hemocytes and it is a typical serine proteinase containing a clip, a proline-rich, and a glycine-rich domain. A recombinant protein containing the clip-domain, with homology to horseshoe crab big defensin and mammalian â-defensin, had antibacterial activity in vitro against gram-positive bacteria.

The proPO activating system (proPO system) is triggered by lipopolysaccharides (LPS) or â-1,3-glucans. An LPS and â-1,3-glucan binding protein (LGBP) was characterized from crayfish hemocytes. The results of an LGBP antibody inhibition assay suggest that LGBP is directly involved in the proPO system.

The primary structure of a crayfish masquerade-like (mas) protein has homology to serine proteinases except for a substitution within the catalytic triad, which renders it without proteinase activity. The crayfish mas-like protein has also binding activity to various gram-negative bacteria and yeast. When the mas-like protein binds to microorganisms, it is processed by a proteolytic enzyme. The mas-like protein exhibited cell adhesion and opsonic activities suggesting that it plays a role in defense against parasites.

For animals that live in a reasonably variable environment the capacity for learning and memory allow them to adapt to the changes they experience. Ecological factors that vary between habitats can affect a range of learning behaviours. Less attention has been directed at how this variation may affect memory processes, or how different ecological variables might interact when shaping cognition and behaviour. Therefore one aim of this thesis was to investigate how different ecological variables shape memory abilities and to test whether those same variables affect other related behaviours such as learning. In order to test this, I selected natural populations of a temperate freshwater fish, the three-spined stickleback (Gasterosteus aculeatus) from pond and river habitats that were proposed to differ in predation pressure, and assayed their learning, memory and other behavioural traits. Pond and river populations differed in their memory and orientation behaviour. An interaction between pond/river habitat and predation pressure affected learning rate, and a similar interaction affected temperament behaviours. Two further studies were conducted to address how captive rearing environments and typical handling procedures affect behaviour in different species. Rearing environment affected memory, but not learning or temperament behaviours in three-spined sticklebacks. Handling caused stress responses in three-spined sticklebacks, Panamanian bishops (Brachyraphis episcopi) and Rainbow trout (Oncorhynchus mykiss), but handling with a water filled scoop compared to a traditional dip-net decreased these responses in three-spined sticklebacks and Panamanian bishops, and also affected behaviour in Panamanian bishops. The results presented in this thesis suggest that ecological variables play a substantial role in shaping learning, memory and other behavioural traits in fish, and highlight the utility of behavioural assays in answering welfare-based questions.

The distribution, biology and ecological impacts of three introduced freshwater teleosts in Western Australia were investigated. The One-Spot Livebearer (Phalloceros caudimaculatus: Poeciliidae), the Swordtail (Xiphophorus helleri: Poeciliidae) and Tilapia or Mozambique Mouthbrooder (Oreochromis mossambicus: Cichlidae), are popular ornamental species that exist in selfsustaining feral populations in the Indian Ocean (Pilbara) or the Southwest Coast Drainage divisions of Western Australia. Phalloceros caudimaculatus is a small (females up to 60, males up to 40 mm TL), non-aggressive, sexually dimorphic poeciliid native to central South America that has existed as a feral species in Western Australia for at least 30 years. A total of 9697 specimens were collected in 12 samples from 2 populations (Bull Creek and Lesmurdie Brook) in metropolitan Perth between September 2002 and April 2003. Dietary and reproductive analyses were conducted on three seasonal samples, i.e. spring, summer and autumn. The diets of individuals in both populations were significantly different though both consisted primarily of vegetal matter and silt/biofilm. Mean total fecundity, size at maturity, and lengths and weights of pregnant fish were lower in fish from Bull Creek, than in those from Lesmurdie Brook. The possible causes of the different observed life history strategies (i.e. reproductive and growth strategies) in both locations are discussed, with temperature considered to be the primary causative factor. A literature review and the results of tank trials with native species determined P. caudimaculatus to be a peaceful species that did not demonstrate the agonistic traits of Gambusia holbrooki. Due to this fact, and the primarily vegetal/detrital diet of P. caudimaculatus, it is proposed that the species may have a lesser impact on native fishes than G. holbrooki. It is also proposed that P. caudimaculatus has displaced G. holbrooki in lentic and lotic systems due to its longer breeding period and greater tolerance to cold temperatures and increased water flow. Xiphophorus helleri is a moderately small (females and males up to at least 70 mm), sexually dimorphic poeciliid native to central and northern South America, that was recently (i.e. 1999) discovered in the Irwin River in the Indian Ocean Drainage Division. A total of 324 specimens were collected between September 2002 and April 2003. Dietary and reproductive analyses were conducted on three seasonal samples, i.e. spring, summer and autumn. The diets of individuals consisted primarily of vegetal matter and silt/biofilm. Mean total fecundity was lower than reported in the literature, i.e. ca 36 compared with ca 60. Oreochromis mossambicus is a large (up to 400 mm TL), aggressive cichlid native to tropical eastern Africa that has existed as a feral species in Western Australia for at least 20 years. A total of 7099 specimens of 0. mossambicus and sympatric species were collected in 3 seasonal samples (spring, summer and autumn) from 2 locations (Gascoyne River and Chapman River) in the Indian Ocean Drainage Division between September 2002 and April 2003. In the Gascoyne River, small (less than 53 mm) 0. mossambicus consumed principally aquatic fauna, while large (greater than 165 mm) 0. mossambicus consumed vegetal matter and silt/biofilm. The diets of 0. mossambicus were significantly different to the sympatric species M cephalus, L. unicolor and H. compressa. Only small (less than 63 mm) 0. mossambicus were collected from the Chapman River. These consumed principally filamentous and unicellular algae. The diets of 0. mossambicus were significantly different to the sympatric species M cephalus, A. butcheri, A. caudavittata, P. olorum, G. holbrooki and H. compressa. In the Gascoyne River, male 0. mossambicus displayed agonistic behaviour towards sympatric species and each other during the extended breeding period.

A recently isolated freshwater methanogenium species, Methanogenium wolfei, is characterized. Cells were irregular cocci, measuring 1.5 to 2.0 micrometers in diameter. No motility was observed, but 1 to 2 flagella per cell were observed after staining with Gray's Flagella Stain. Colonies formed by this species were small, shiny, and green-brown in color. Formate or hydrogen plus carbon dioxide served as substrates for growth. The optimal temperature for growth was found to be 45 degrees centigrade with minimal growth below 30 degrees centigrade and above 55 degrees centigrade. The optimal pH for growth was determined to be 6.8. Optimal growth was obtained within a 0.0 to 0.2M range of added sodium chloride. Acetate and arginine were required for growth. DNA base composition was 61.1 mol%. G+C. The presence of coenzyme F-420 at a concentration of 134 mg/kg cells (wet weight) was determined in cell extracts. The enzyme NADP reductase was found to be present and was partially characterized.

This biogeographical study documents the modern distribution of ostracodes in the southwest Yukon Territory and northern British Columbia, Canada. The study tested the hypothesis that dissolved ion composition and concentrations of the lake water are the primary determinants of the distribution of modern ostracodes in this region. A total of 28 freshwater species representing 8 genera were identified in the 33 study lakes. Species common in the southwest Yukon are widely distributed throughout North America, and include Cyclocypris ampla, Candona candida, Cypria turneri, Cypria ophtalmica, and Candona protzi. Concentrations of ostracode valves were highest in four lakes with moderate conductivity values ranging between 330 and 397 muS/cm. Rarefaction estimated species richness was low (3 to 8), and the highest estimated species richness was found in four lakes, three of which were within 1 km of each other. Conductivities in these lakes ranged between 320 and 397 muS/cm. There is little geographic pattern in either species richness or in the distribution of common species. The dissolved ion composition is the primary control determining the species that will be present in a particular lake.

Carp (Cyprinus carpio) are alien freshwater fish that are globally widespread and often associated with highly degraded freshwater ecosystems. This study explored carphabitat interactions that could contribute to the worldwide distribution of, and consequent ecological impacts by, carp. Particular emphasis was placed on the role of carp size in these interactions. One component of this study involved a field experiment that was used to quantify the effects of carp biomass density and size-structure on freshwater invertebrate communities and water quality. The treatments in this field experiment comprised different combinations of large (2 kg) and small (0.7 kg) carp, and low (330 kg.ha-1), intermediate (570 kg.ha-1) and high (650 kg.ha-1) biomass densities. Carp impacts were more carp size-dependent than described in previous studies. In particular, carp size was more important than carp biomass density in determining the concentration of total phosphorus and algal biomass. On the other hand, a more even mix of carp sizes increased total nitrogen. The zooplankton and macroinvertebrate taxa that were more abundant in the presence of carp were the taxa most able to avoid carp predation and tolerate habitat changes caused by carp benthivory. To complement the small-spatial scale field experiment, large-scale patterns of carp distribution, biomass density and recruitment were explored among the rivers of New South Wales (Australia) in relation to their physical habitat. In contrast to expectations, and although most recruitment probably occurred at lower-altitudes, the populations with a size structure and biomass density most likely to cause ecological degradation occurred at intermediate altitudes. Furthermore, the distribution of smaller carp (less than or equal to 100 mm, and less than or equal to 300 mm) indicated that the regulation of river flows does not always favour carp populations, particularly during drought conditions. Nevertheless, it was concluded in a review of the carp literature, which incorporated the findings of this study, that invasion by alien carp is most successful in streams with formerly highly variable flows that are now subject to flow regulation. Moreover, carp are likely to enhance their advantage in these waters through habitat modification.

The general aim of this thesis was to examine the merits of ex-situ vs. in-situ strategies for the conservation of the endangered freshwater pearl mussel, Margaritifera margaritifera, and to investigate the relationship of the larval parasitic stages of the mussel (glochidia) with the salmonid hosts. To this end, I critically reviewed the literature on conservation of freshwater mussels, developed methods for quantifying the behaviour and activity patterns of adult mussels in captivity, experimentally studied host specificity, and quantified the physiological and behavioural effects of glochidia upon salmonid hosts. The results indicate that the conservation of the freshwater pearl mussel is probably best addressed at the watershed scale, and will benefit from a combination of ex-situ and in-situ techniques, as well as from a more critical assessment of findings, many of which are only reported in the grey literature. Empirical, peer-reviewed data are badly needed to inform current conservation efforts. Novel Hall-effect magnetic sensors were used to quantify and characterise discrete mussel behaviours without adversely affecting the welfare or survival of adult mussels, and these hold considerable potential for determining optimal rearing conditions for ex-situ conservation. Arctic charr was shown to be a potentially suitable host for M. margaritifera, and occupied an intermediate position in host suitability between brown trout and Atlantic salmon. Physiological impacts of glochidia upon brown trout included swelling of secondary lamellae and spleen enlargement, but the latter tended to be slight and was restricted to 1 month post-exposure. Glochidia encystment had no significant effect on blood haematocrit, respiratory performance, or cryptic colouration of brown trout hosts. The behavioural effects were more subtle and glochidiosis made brown trout more risk-averse and less willing to explore a novel habitat, without affecting the host's ability to chemically recognise and avoid cues from a predator. Overall, the results of this thesis indicate that the impacts of glochidia upon salmonid hosts are probably slight and temporally variable, and may perhaps lead to increased host survival, which would support the symbiosis-protocooperation theory of glochidia-salmonid interaction.

Monotypic stands of the macrophytes Peltandra virginica and Spartina cynosuroides, which shared a common boundary, were studied at Sweethall Marsh, a tidal freshwater marsh located on the Pamunkey River within the Chesapeake Bay estuarine system, Virginia. Compartmental models indicate that both Peltandra and Spartina take up, internally cycle, and release to the environment, significant levels of nitrogen and phosphorus. Models also suggest that Peltandra and Spartina and their associated sediment compartments are capable of regulating nitrogen and phosphorus fluxes through their uptake and storage capacity. Nitrogen use efficiency was significantly higher in the shoots and roots of Spartina compared to Peltandra, while rhizome use efficiency was slightly higher in Peltandra. Phosphorus use efficiency was significantly higher in shoots, roots, and rhizomes of Spartina than in Peltandra. Lower use efficiency in Peltandra demonstrates a greater demand of nutrient per unit biomass than Spartina. Nitrogen and phosphorus recovery efficiency was higher in Peltandra. Efficiency indexes suggest that although Spartina appears to use nitrogen and phosphorus more efficiently for growth, Peltandra recovers and stores these nutrients more efficiently. Peltandra shoot, root, and rhizome tissue nutrient levels appear independent of sediment nitrogen and phosphorus availability. Spartina shoot, root, and rhizome nitrogen levels, however, appear dependent on sediment total nitrogen and total phosphorus. The relationship of Peltandra tissue nutrient levels to sediment availability is explained in terms of the rhizome storage capacity and reallocation of nitrogen and phosphorus to support productivity patterns. Spartina, however, must rely more on de novo root uptake to meet nutrient demands. Shoot, root, and rhizome nitrogen and phosphorus standing stocks were strongly correlated in both Peltandra and Spartina while sediment standing stocks were not. Nitrogen to phosphorus ratios were higher in the shoots than the roots and rhizomes of both Peltandra and Spartina reflecting the levels of nitrogen required to support photosynthesis. Nitrogen to phosphorus ratios varied over the sampling period, however appeared to converge on an "optimum" ratio. The correlation of nitrogen and phosphorus suggests an interaction between these nutrients although this relationship is unclear. Apparently both Peltandra and Spartina reallocate, as well as require, nitrogen and phosphorus in certain ratios which maximize productivity, uptake, and carbon assimilation.

Life histories are known to vary across geographic ranges in response to a number of factors, both biotic and abiotic. Environmental calcium availability has been shown to affect freshwater gastropod life histories due to its fundamental requirement in shell formation. Adaptation of life histories to local environmental conditions may cause the response to novel pollutants to vary across populations within a species due to trade-offs between and among traits but very few studies have examined wide scale variation in life history response to stress across geographic ranges. A long term study was conducted and aimed to expand on current understanding by rearing populations of the great pond snail, Lymnaea stagnalis sampled from across the UK, for two generations in high and low calcium environments. A comprehensive suite of life histories was recorded throughout the study and traits were compared between populations and treatments, and across generations to distinguish between environmental, plastic and heritable sources of variation. Further work focussed on life history trade-offs under different environmental conditions before utilising a stage-classified matrix model to derive population growth rates (λ) and compare effects across populations and calcium treatments. Finally, acute and chronic effects of exposure to nanoparticulate carbon black were assessed before using matrix models to investigate the combined effects of environmental calcium with nanoparticulate carbon black on λ for three populations of snails. Significant intra-specific variation was recorded in the majority of life history traits, which were shown to display high levels of phenotypic plasticity as the norm. Intergenerational comparisons revealed that traits more directly linked to fitness, such as size at reproduction and reproductive output, showed higher heritabilities than those pertaining to growth, such as growth rates and age at first reproduction. Both generalised and population specific responses to calcium availability were shown in life history traits across the study populations. These effects tended to be subtle but suggest that environmental calcium plays a role in shaping life history strategies across the UK distribution. Life history trade-offs between traits tended to be conserved across populations, and showed little response to environmental calcium, although differential investment in life history traits across calcium treatment was detected in some cases. A strong trade-off between age and size at first reproduction was detected across all generations and calcium treatments. Size at first reproduction was also shown to correlate with reproductive output, wherein a trade-off between eggs per mass and number of egg masses was detected. Traits involved in trade-offs appeared to more strongly associate with fitness and these findings suggest that trade-offs between key life history traits are of importance in understanding population specific life history strategies. Stage-classified matrix modelling showed a trend towards reduced λ in low calcium but this trend was not significant. A significant reduction in λ across generations was recorded which was most likely to be the result of inbreeding. Local adaptation to calcium availability was shown to influence the life history response to nanoparticulate carbon black, and was mirrored in predicted population growth rates obtained from matrix models. Intraspecific differences in response to carbon black nanoparticles only became apparent when calcium concentrations were low. These findings would support the view that in order to be better able to predict the response of species to the presence of novel stressors such as nanoparticles, it is necessary to account for intraspecific adaptation of life history traits as well as geographical variation in the environmental context.

A majority of carbon in freshwater and marine ecosystems is in the form of ultraplankton, heterotrophic and autotrophic plankton &<&5 &\mu&m including heterotrophic bacteria, Prochlorococcus, cyanobacteria, and autotrophic eucaryotes. However, ultraplankton and subsequently microbial food webs have yet to be incorporated into models of benthic-pelagic coupling despite the preponderance of macroinvertebrates with the capacity to feed on ultraplankton. I have examined the role of microbial food webs in benthic-pelagic coupling in three ecosystems: Lake Baikal, Siberia, Russia; Gulf of Maine, Northwest Atlantic Ocean; and Conch Reef, Florida Keys, USA. Using sponges as a model organism and in situ measurements, I have quantified (1) suspension feeding on ultraplankton and (2) release of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) resulting in direct evidence that benthic macroinvertebrates do occupy the level of primary consumer within the microbial food web. Dual-beam flow cytometry was employed to quantified sponge suspension feeding on five types of ultraplankton: heterotrophic bacteria, Synechococcus-type cyanobacteria, autotrophic picoplankton &<&3 &\mu&m, autotrophic eucaryotes 3-10 &\mu&m, and in marine ecosystems Prochlorococcus. Grazing by the freshwater sponges Baikalospongia intermedia and B. bacilliferia and the boreal marine sponge, Mycale lingua, was unselective for all types of ultraplankton with efficiencies ranging from 63-99%. This is the first time that grazing on Synechococcus-type cyanobacteria and Prochlorococcus by macroinvertebrates has been quantified in freshwater and marine ecosystems. Conversely, the coral reef sponges Ircinia felix and I. strobilina release significant amounts of DIN and DIP as a result of grazing on procaryotic plankton. Using a general model for organism-mediated fluxes, it is conservatively estimated that through active suspension feeding sponges in Lake Baikal retain 1.97 g C day&\sp{lcub}-1{rcub}& m&\sp{lcub}-2{rcub}& and M. lingua retains 29 mg C day&\sp{lcub}-1{rcub}& m&\sp{lcub}-2{rcub}& while at Conch Reef sponges released 204 &\mu&mol DIN day&\sp{lcub}-1{rcub}& m&\sp{lcub}-2{rcub}& and 48 &\mu&mol DIP day&\sp{lcub}-1{rcub}& m&\sp{lcub}-2{rcub}&. A majority of the carbon retained at all three locations was from procaryotic cell types suggesting that ultraplankton are an important overlooked component of benthic-pelagic coupling.

Australian freshwaters are home to approximately 256 fish species from 36 families, many of which are endemic to the country and considered threatened, vulnerable or rare in the wild. In part this is due to a long history of continental isolation where increasing aridity and flow unpredictability have given rise to a fish fauna characterised by a unique association of life-history traits (i.e. characteristics of an organism that contribute to its fitness or performance, and which allow it to function in the environment) in order to cope with natural variation in environmental seasonality, stability and predictability. My thesis presents an assessment of life- history traits and the functional diversity (the range and value of organismal characteristics) of Australian freshwater fish at multiple spatial scales (i.e. continental, river basin, catchment and population scales), with an emphasis on phylogenetic relationships, environmental determinants and conservation biology.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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