Bacterial communities are fundamental components of many processes occurring in aquatic ecosystems, since through microbial activities substantial amount of matter and energy is transferred from a pool of DOC to higher trophic levels. Previous studies highlighted the beneficial effects of diversity on ecosystem functioning, however studies on the resistance and resilience in microbial communities are scarce. Similarly, studies focusing on factors that might improve resistance or resilience of communities such as the influence of refuges are equally missing, although an understanding of the underlying mechanisms could be very useful in the field of conservation management. In this study, chemostat cultures were used to investigate the influence of a spatial and a temporal refuge on bacterioplankton communities’ resistance and resilience measured in terms of functioning and community composition after applying a salinity pulse disturbance. Respiration rate and substrate utilization were used to estimate bacterial functioning while community composition was determined by using T-RFLP. The perturbation was found to affect bacterial functioning and community composition. Moreover our findings indicate that the resistance and resilience measured in terms of bacterial functioning and community composition were significantly influenced by the provision of refuges.

The overall aim of this thesis was to investigate the fate of perfluorinated alkyl compounds (PFCs) in biological systems. During the past several years, it has been shown that wildlife are ubiquitously contaminated with two classes of PFCs, the perfluoroalkyl carboxylates (CxF2x+1C(O)OH, PFCAs) and sulfonates (CxF2x+1SO3H, PFSAs). However, there is still considerable uncertainty regarding how wildlife are accumulating these PFCs, particularly in remote areas such as the Canadian arctic. The potential for fluorotelomer acrylate monomers (CxF2x+1CH2CH2OC(O)CH=CH2, FTAcs) to act as precursors to PFCAs through atmospheric oxidation was investigated using smog chamber experiments. FTAc atmospheric fate is determined by OH radical reaction with a lifetime of approximately 1 day. The sole primary product of this reaction was the 4:2 fluorotelomer glyoxylate which is expected to undergo further atmospheric oxidation or photolysis to ultimately yield PFCAs. Temporal and spatial trends of PFCs in arctic ringed seals and seabirds were investigated to assist in understanding PFC transport mechanisms to remote regions. In ringed seals, perfluorooctane sulfonate (PFOS) levels decreased rapidly, coinciding with the phase out by the major manufacturer. These findings are consistent with volatile precursors as the dominant source of PFCs to arctic wildlife. The bioaccumulation and biotransformation of the 8:2 FTAc was investigated in two complimentary studies with rainbow trout. During the in vivo dietary exposure study, fish rapidly accumulated and biotransformed the 8:2 FTAc, with intermediate metabolites observed within 1 hour of dosing. Perfluorooctanoate (PFOA), perfluorononanoate (PFNA) and perfluoroheptanoate (PFHpA) were formed and accumulated in low yields. The carboxylesterase activity in the trout liver and stomach was investigated using in vivo sub-cellular (S9) incubations. Very high esterase activities were shown with approximately equal efficiency in the stomach and liver. The metabolic pathway of the 8:2 fluorotelomer alcohol (8:2 FTOH) was investigated by separately dosing whole rainbow trout with three intermediate metabolites that represented important branching points. The 7:3 fluorotelomer saturated carboxylate (FTCA) did not form PFOA, but formed PFHpA and the 7:3 fluorotelomer unsaturated carboxylate (FTUCA). The 8:2 FTCA and 8:2 FTUCA did form PFOA, confirming a “beta-like-oxidation” mechanism.

The overall aim of this thesis was to investigate the fate of perfluorinated alkyl compounds (PFCs) in biological systems. During the past several years, it has been shown that wildlife are ubiquitously contaminated with two classes of PFCs, the perfluoroalkyl carboxylates (CxF2x+1C(O)OH, PFCAs) and sulfonates (CxF2x+1SO3H, PFSAs). However, there is still considerable uncertainty regarding how wildlife are accumulating these PFCs, particularly in remote areas such as the Canadian arctic. The potential for fluorotelomer acrylate monomers (CxF2x+1CH2CH2OC(O)CH=CH2, FTAcs) to act as precursors to PFCAs through atmospheric oxidation was investigated using smog chamber experiments. FTAc atmospheric fate is determined by OH radical reaction with a lifetime of approximately 1 day. The sole primary product of this reaction was the 4:2 fluorotelomer glyoxylate which is expected to undergo further atmospheric oxidation or photolysis to ultimately yield PFCAs. Temporal and spatial trends of PFCs in arctic ringed seals and seabirds were investigated to assist in understanding PFC transport mechanisms to remote regions. In ringed seals, perfluorooctane sulfonate (PFOS) levels decreased rapidly, coinciding with the phase out by the major manufacturer. These findings are consistent with volatile precursors as the dominant source of PFCs to arctic wildlife. The bioaccumulation and biotransformation of the 8:2 FTAc was investigated in two complimentary studies with rainbow trout. During the in vivo dietary exposure study, fish rapidly accumulated and biotransformed the 8:2 FTAc, with intermediate metabolites observed within 1 hour of dosing. Perfluorooctanoate (PFOA), perfluorononanoate (PFNA) and perfluoroheptanoate (PFHpA) were formed and accumulated in low yields. The carboxylesterase activity in the trout liver and stomach was investigated using in vivo sub-cellular (S9) incubations. Very high esterase activities were shown with approximately equal efficiency in the stomach and liver. The metabolic pathway of the 8:2 fluorotelomer alcohol (8:2 FTOH) was investigated by separately dosing whole rainbow trout with three intermediate metabolites that represented important branching points. The 7:3 fluorotelomer saturated carboxylate (FTCA) did not form PFOA, but formed PFHpA and the 7:3 fluorotelomer unsaturated carboxylate (FTUCA). The 8:2 FTCA and 8:2 FTUCA did form PFOA, confirming a “beta-like-oxidation” mechanism.

The variation of Arginine kinase (Ark) genotype frequency among populations of Thais clavigera has been reported in previous study. However, the difference which is originated from self-seeding or differential selection after recruitment is not understood. To answer this question, the spatial (i.e. Shainsan, Taisi, Budai, and Chiku) and temporal (sell length: <15mm, 15-20mm, 20-30mm, 30-40mm, and >40mm; year: 2001 and 2003) variations of Ark allozyme were examined by starch gel electrophoresis. There was no significant difference in the ratio of Ark genotypes (ark63/63, ark63/100, ark100/100) in the size range of <15mm among Shainsan, Taisi and Chiku. The result indicated that the populations of T. clavigera is from the same recruitment. In the size range of 15-20mm, the frequency of ark63/63 increased from southern to northern populations, i.e. 0.21(Chiku) < 0.33(Budai) < 0.60(Taisi) < 0.66(Shainsan), respectively. It is proposed that the variation of Ark genotypes among populations is resulting from stress of temperature or dessication. A significant difference in the ratio of Ark genotypes was found in the population of Taisi with the size range of 30-40mm. Besides, the frequency of Ark genotypes among populations was not related to the degree of imposex.

This thesis investigates variability in airway caliber and the distribution of ventilation within the human lung as thought to occur in asthma. Currently, the understanding of how an integrated network of airways can lead to temporal and spatial variation as found in the human lung is unclear. Throughout this thesis, a multibranch airway tree model was used in a forward modeling approach. In a variability study, the mean airway resistance (RL) was observed to be proportional to the standard deviation in airway resistance (SDRL) as reported in the literature under several conditions of airway diameter indicating the strong robustness of this behavior. The model predicted previously reported RL distributions and the reported proportionality of SDRL and RL, but only when we included coherency between airways. In a second study, patient specific ventilation was investigated using an image functional approach by closing specific airways (creating defects) identified by hyperpolarized 3He MRI from asthmatic subjects. Impedance predictions from the imposed heterogeneous ventilation were then calculated and correlated to 3He MRI ventilation defect percent (VDP), plethysmography, and spirometry data. These predictions suggest the forced oscillation technique (FOT) to be a superior metric toward the evaluation of the VDP. In a third study, we investigated how asymmetric branching could play a role in ventilation defect emergence and persistence. At high muscle activation levels simulating an asthmatic episode, airway trees with greater asymmetry reached steady state sooner, with defects that were more persistent in location, had lower RL values (~50%), and greater EL values (~25%) after bronchoconstriction. These results suggest the initial formation of ventilation defects was dependent on airway instability; however, the location and persistence of ventilation defects may be due to geometric airway structure. By modeling the contribution of ventilation defects to lung impedance, we were able to show that defects can play a role in governing the relationship between RL and its variation, and the effect of defects through VDP could be better assessed using FOT. Moreover, lung structure contributed to the emergence and persistence of ventilation defects, meaning that defects could be potentially ameliorated through structural intervention.

The overall aim of this thesis was to investigate the fate of perfluorinated alkyl compounds (PFCs) in biological systems. During the past several years, it has been shown that wildlife are ubiquitously contaminated with two classes of PFCs, the perfluoroalkyl carboxylates (CxF2x+1C(O)OH, PFCAs) and sulfonates (CxF2x+1SO3H, PFSAs). However, there is still considerable uncertainty regarding how wildlife are accumulating these PFCs, particularly in remote areas such as the Canadian arctic. The potential for fluorotelomer acrylate monomers (CxF2x+1CH2CH2OC(O)CH=CH2, FTAcs) to act as precursors to PFCAs through atmospheric oxidation was investigated using smog chamber experiments. FTAc atmospheric fate is determined by OH radical reaction with a lifetime of approximately 1 day. The sole primary product of this reaction was the 4:2 fluorotelomer glyoxylate which is expected to undergo further atmospheric oxidation or photolysis to ultimately yield PFCAs. Temporal and spatial trends of PFCs in arctic ringed seals and seabirds were investigated to assist in understanding PFC transport mechanisms to remote regions. In ringed seals, perfluorooctane sulfonate (PFOS) levels decreased rapidly, coinciding with the phase out by the major manufacturer. These findings are consistent with volatile precursors as the dominant source of PFCs to arctic wildlife. The bioaccumulation and biotransformation of the 8:2 FTAc was investigated in two complimentary studies with rainbow trout. During the in vivo dietary exposure study, fish rapidly accumulated and biotransformed the 8:2 FTAc, with intermediate metabolites observed within 1 hour of dosing. Perfluorooctanoate (PFOA), perfluorononanoate (PFNA) and perfluoroheptanoate (PFHpA) were formed and accumulated in low yields. The carboxylesterase activity in the trout liver and stomach was investigated using in vivo sub-cellular (S9) incubations. Very high esterase activities were shown with approximately equal efficiency in the stomach and liver. The metabolic pathway of the 8:2 fluorotelomer alcohol (8:2 FTOH) was investigated by separately dosing whole rainbow trout with three intermediate metabolites that represented important branching points. The 7:3 fluorotelomer saturated carboxylate (FTCA) did not form PFOA, but formed PFHpA and the 7:3 fluorotelomer unsaturated carboxylate (FTUCA). The 8:2 FTCA and 8:2 FTUCA did form PFOA, confirming a “beta-like-oxidation” mechanism.

The overall aim of this thesis was to investigate the fate of perfluorinated alkyl compounds (PFCs) in biological systems. During the past several years, it has been shown that wildlife are ubiquitously contaminated with two classes of PFCs, the perfluoroalkyl carboxylates (CxF2x+1C(O)OH, PFCAs) and sulfonates (CxF2x+1SO3H, PFSAs). However, there is still considerable uncertainty regarding how wildlife are accumulating these PFCs, particularly in remote areas such as the Canadian arctic. The potential for fluorotelomer acrylate monomers (CxF2x+1CH2CH2OC(O)CH=CH2, FTAcs) to act as precursors to PFCAs through atmospheric oxidation was investigated using smog chamber experiments. FTAc atmospheric fate is determined by OH radical reaction with a lifetime of approximately 1 day. The sole primary product of this reaction was the 4:2 fluorotelomer glyoxylate which is expected to undergo further atmospheric oxidation or photolysis to ultimately yield PFCAs. Temporal and spatial trends of PFCs in arctic ringed seals and seabirds were investigated to assist in understanding PFC transport mechanisms to remote regions. In ringed seals, perfluorooctane sulfonate (PFOS) levels decreased rapidly, coinciding with the phase out by the major manufacturer. These findings are consistent with volatile precursors as the dominant source of PFCs to arctic wildlife. The bioaccumulation and biotransformation of the 8:2 FTAc was investigated in two complimentary studies with rainbow trout. During the in vivo dietary exposure study, fish rapidly accumulated and biotransformed the 8:2 FTAc, with intermediate metabolites observed within 1 hour of dosing. Perfluorooctanoate (PFOA), perfluorononanoate (PFNA) and perfluoroheptanoate (PFHpA) were formed and accumulated in low yields. The carboxylesterase activity in the trout liver and stomach was investigated using in vivo sub-cellular (S9) incubations. Very high esterase activities were shown with approximately equal efficiency in the stomach and liver. The metabolic pathway of the 8:2 fluorotelomer alcohol (8:2 FTOH) was investigated by separately dosing whole rainbow trout with three intermediate metabolites that represented important branching points. The 7:3 fluorotelomer saturated carboxylate (FTCA) did not form PFOA, but formed PFHpA and the 7:3 fluorotelomer unsaturated carboxylate (FTUCA). The 8:2 FTCA and 8:2 FTUCA did form PFOA, confirming a “beta-like-oxidation” mechanism.

This study investigates the variation in the spatial patterns of Diptera and Collembola throughout the forest canopy due to seasonal changes in temperature and humidity in the monsoon climate of West Africa. There is a very distinct turnover in climate from the end of the dry season (the hottest and driest time of the year) to the beginning of the rains and this coincides with significant increases and decreases in the overall abundance of many forest dwelling Diptera and Collembola species. The study investigates spatial patterns on two gradients; vertically from the ground to the high canopy and laterally from the edge of the forest to the core, with the added complexity of the affects of anthropogenic burning of adjacent savannah. The results show that seasonality and the starting of the rains significantly affect both the overall abundance and the spatial patterns, providing species with a strategic change in habitat niche. During seasonal conditions that are less conducive to species' overall abundance, spatial patterns are suppressed by environmental conditions. However when environmental conditions are optimum for increased species abundance, spatial patterns are only suppressed by the availability of resources within the habitat (feeding or reproductive resources for example). Successive late burning events may have changed the structure of the forest edge introducing a significantly more open forest structure changing environmental conditions and thus creating a habitat more suitable for species which prefer lower humidity and higher temperatures.

Small timing differences occur when sounds reach one ear before the other, creating interaural phase differences (IPDs). The phase-locked activity in the auditory nerve can, at low frequencies, preserve IPDs. IPDs are used for localising and separating sounds from different directions. Chapters 3, 5, and 6 report three studies of the independent effects of age and sensorineural hearing loss on the temporal processing of sound that aids spatial hearing. Chapters 2 and 4 describe two supporting methodological studies. Chapter 2 compared the duration of training required for stable IPD-discrimination thresholds for two stimulus presentation procedures. The procedure requiring the least training was adopted for subsequent studies. Age and hearing loss are related and both may affect sensitivity to IPDs. Chapter 3 demonstrated that hearing loss, regardless of listener age, is related to poorer sensitivity to IPDs in the temporal fine structure (TFS), but not in the temporal envelope. Chapter 3 also showed that age, independent of hearing loss, is related to poorer envelope-IPD sensitivity at low modulation rates, and somewhat poorer TFS-IPD sensitivity. In Chapter 5, listener age and IPD sensitivity were both compared to subcortical neural phase locking measured through the frequency-following response (FFR). Phase coherence in the envelope-FFR at 145 Hz modulation and in the TFS-FFR deteriorated with age, suggesting less precise phase locking in old age. However, age-related changes to IPD sensitivity were not strongly related to age-related changes in FFR phase coherence. IPD sensitivity declines may be predominantly caused by deterioration of binaural processing independent of subcortical phase locking. Chapter 4 showed that electrodes at the mastoids recorded TFS-FFR generated earlier in the auditory pathway than electrodes from the nape of the neck to forehead, which recorded FFR generated later in the brainstem. However, these electrode montages did not reveal different age- or hearing-loss-related FFR deficits in Chapter 5. Chapter 6 determined whether hearing loss affected the ability to use TFS IPDs to achieve better speech perception. On average, old hearing-impaired listeners gained a small, but significant, benefit from a lateral separation of the speech sources. Replacing the TFS with binaurally in-phase sine waves (removing the TFS IPDs) significantly reduced the benefit of lateral separation. How much a listener benefitted from intact TFS IPDs in speech perception was strongly related to the extent of their hearing loss at low frequencies and their monaural processing of TFS, but not to their ability to discriminate IPDs. In general, this thesis shows that low-frequency hearing loss is associated with poor sensitivity to TFS IPDs and the ability to benefit from them when sounds are laterally separated. The thesis also shows that old age can reduce sensitivity to IPDs and weaken subcortical temporal coding. Although only partly related, these effects are likely to cause problems for old individuals in challenging listening environments.

O objetivo do trabalho foi caracterizar a transmissão de dengue nas regiões de São José do Rio Preto e Araçatuba, entre 1990 e 1996. Analisaram-se os Coeficientes de Incidência (CI) de casos confirmados laboratorialmente e autóctones de dengue segundo áreas, sexo e idade. Analisaram-se as curvas de CI mensais para as regiões, sub-regiões e municípios. Realizou-se análise espacial, relacionando-se os CI com variáveis sócio-econômicas e demográficas. Construíram-se curvas de CI semanais de casos suspeitos e confirmados laboratorialmente de dengue para investigar a relação entre elas. Os CI obtidos apontam para o risco de ocorrência de dengue hemorrágica. Verificaram-se maiores CI para as mulheres e para pessoas entre 30 e 59 anos. Nos dois últimos períodos estudados, notaram-se, para as várias sub-regiões, maiores níveis de incidência e aumento do número de meses com transmissão, indicando uma possível tendência de endemização da doença. Verificou-se que foi pelos municípios maiores que a transmissão, em geral, se iniciou e se encerrou, e que neles a freqüência de períodos com transmissão foi maior. Verificou-se também, que, nos municípios com melhores situações de instrução, renda e maiores populações, ocorreu, em maior proporção, CI de valores mais altos, podendo, este fato, estar relacionado com a atração exercida por eles. Estas evidências mostram que um possível fator de risco a ser utilizado, em uma estratificação de medidas de controle, seria o tamanho do município. Foram obtidas relações entre as séries de CI de casos suspeitos e confirmados laboratorialmente de dengue, possibilitando-se estimar as últimas a partir das primeiras. / This study aims to characterize the dengue transmission in th e regions of São José do Rio Preto and Araçatuba, São Paulo, between 1990 and 1996. Incidence Rates (IR) of in laboratory confirmed dengue cases as well as autochthonous dengue cases have been analyzed according to areas, gender and age. Monthly IR curves have been analyzed for the regions, sub-regions and municipal districts. A spatial analysis has been carried out relating the IR with social-economical and demographic variables. Weekly IR curves of both suspected cases and in laboratory confirmed dengue cases have been built in order to investigate the relationship between them. The obtained IR point for a risk of hemorrhagic dengue occurrence. It was noticed a higher risk of dengue occurrence for women and among people between 30 and 59 years. In the last studied periods it was also noticed greater incidence in several sub-areas and increase of month periods with transmission, indicating a possible disease spreading. The transmission, in general, started and finished in large municipal districts, and in those the transmission period was more frequent. It was also observed that, in large municipal districts with better educational level and income variables, IR showing higher levels occured in a larger exrtent than in smaller ones whose indicators of those variables were worst, and the explanation for this can be related with the attraction exercised by the great population centers. These evidences have showed that a possible risk factor to be used in the stratification of the control measures would be the size of the municipal district. It was obtained the relationship between the IR series of suspected dengue cases and in laboratory confirmed cases enabling us to measure the last ones starting from the first ones.