No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Eukaryotic cells rapidly modulate protein synthesis in response to environmental cues through the reversible phosphorylation of eukaryotic initiation factor 2 (eIF2α~P) by a family of eIF2α kinases. The eIF2 delivers initiator Met-tRNAiMet to the translational apparatus, and eIF2α~P transforms its function from a translation initiation factor into a competitive inhibitor of the guanine nucleotide exchange factor (GEF) eIF2B, which is responsible for the recycling of eIF2-GDP to the translationally-competent eIF2-GTP state. Reduced eIF2-GTP levels lower general protein synthesis, which allows for the conservation of energy and nutrients, and a restructuring of gene expression. Coincident with global translational control, eIF2α~P directs the preferential translation of mRNA encoding ATF4, a transcriptional activator of genes important for stress remediation. The term Integrated Stress Response (ISR) describes this pathway in which multiple stresses converge to phosphorylate eIF2α and enhance synthesis of ATF4 and its downstream effectors. In this study, we used sucrose gradient ultracentrifugation and a genome-wide microarray approach to measure changes in mRNA translation during ER stress. Our analysis suggests that translational efficiencies vary across a broad range during ER stress, with the majority of transcripts being either repressed or resistant to eIF2α~P, while a notable cohort of key regulators are subject to preferential translation. From this latter group, we identify IBTKα as being subject to both translational and transcriptional induction during eIF2α~P in both cell lines and a mouse model of ER stress. Translational regulation of IBTKα mRNA involves the stress-induced relief of two inhibitory uORFs in the 5’-leader of the transcript. Also identified as being subject to preferential translation is mRNA encoding the bifunctional aminoacyl tRNA synthetase EPRS. During eIF2α~P, translational regulation of EPRS is suggested to occur through the bypass of a non-canonical upstream ORF encoded by a CUG start codon, highlighting the diversity by which upstream translation initiation events can regulate expression of a downstream coding sequence. This body of work provides for a better understanding of how translational control during stress is modulated genome-wide and for the processes by which this mode of gene regulation in the ISR contributes to cell fate.

Indiana University-Purdue University Indianapolis (IUPUI) / Strawberry (Fragaria spp.) is an agricultural crop grown often in temperate regions that has high variability in its susceptibility to freezing injury. To breed cultivars for frost and freezing tolerance, identification of molecular markers associated with low temperature tolerance is advantageous. In this work, I investigated a high-throughput method for protein assays and western blotting. Success in streamlining these processes saves an immense amount of time and allows for the processing of more samples and obtaining larger datasets. Thirty-three octoploid varieties were tested for their accumulation of five different potential biomarkers in response to cold exposure. It was found that total dehydrin content, has the strongest potential to be reliable biomarkers for breeding programs. Previous work identified seven putative dehydrins in Fragaria, where two were purified and positively identified by mass spectrometry and determined to be COR47-like (SKn) and XERO2-like (YnSKn). This work demonstrated that cold tolerance positively correlated with dehydrin protein expression levels. To understand the cold-regulated expression of dehydrins as a function of cold exposure time, the levels of transcripts and corresponding proteins were examined in strongly cold tolerant (Alta) and lesser cold tolerant (FDP817, NCGR1363) Fragaria diploid genotypes. The COR47-like (SKn) and XERO2-like (YnSKn) dehydrins both had higher transcript accumulation and protein levels in the more cold tolerant line in comparison to the two less cold tolerant lines. Lack of correlation between transcript and resulting COR47 protein level in Alta were observed at several different timepoints, where protein accumulation preceded an increase in RNA. This trend was not seen with XERO2. This initiated an investigation to discover at what level COR47 is being regulated. First, the COR47 coding region was sequenced for all the genotypes to confirm against the predicted sequence. In addition, since two isoforms of the COR47 gene exist, and could possibly explain the discrepancy in transcript counts, primers were designed for both isoforms and RT-qPCR was performed to examine the transcripts of COR47 more closely. Through examination of the non-congruence of COR47 transcripts and protein, it was found that transcriptional mechanisms of regulation are not involved, and that post transcriptional and post-RNA splicing mechanisms are likely to be responsible for the observed trend in Alta. Conclusions from this work demonstrate that dehydrin transcripts and dehydrin protein accumulations are strong potential biomarkers for identifying low temperature tolerance in diploid strawberry.

<p>  </p> <p>Glucocorticoids (GC) play a critical role in regulating the physiological response to stress. Disruptions to baseline levels due to stress can have negative implications on a variety of factors including growth and development, physical body conditions, metabolism, immune functions, and expression of normal behaviors, although this list is not exhaustive. When birds are unable to adapt to the stressor and return to homeostasis, the energy expenditure associated with the failed attempt at coping can lead to significant declines in the overall health, welfare, production, and performance of the bird. This can go on to impact producers and consumers as well, indicating the extensive repercussions of stress. Recently, scientists have been investigating thorough and efficient methods of quantifying stress in birds, such as measuring heterophil-to-lymphocyte ratio (HLR) or detecting glucocorticoid levels through enzyme-linked immunoassays (ELISA). However, the precise mechanism behind HLR increase during stress is unknown and ELISAs may not provide accurate results depending on when the blood is being measured. </p> <p><br></p> <p>GC are differentially released and exert their effects in a manner that is dependent on sex, age, and time. However, before investigating this, it was critical to validate the GC kits to ensure that they were measuring cortisol and corticosterone separately along with zero cross reactions with other precursors. Chapter 2 had 4 experiments carried out. The objective of experiment 1 was to validate ELISAs to ensure that they were measuring the GC accurately and separately since both cortisol and corticosterone were being measured. To do this, duck serum was pooled and charcoal-stripped to remove the presence of steroids. 3 standard curves were run to confirm that there was no cross reactivity. The objective of experiment 2 was to further validate the ELISA kits with mass spectrometry by checking for both glucocorticoids in the pooled samples. Once the validation process was complete, experiment 3 was carried out to look at the effect of ACTH stimulation on GC release. 16-week-old drakes and hens were given either intramuscular (IM) injections of cosyntropin (0.06 mg/kg) or saline as control. The cosyntropin dose was chosen according to previous studies reporting relatively high physiological responses, therefore, we wanted to replicate this. N was 10/sex/treatment. Blood was then collected at 0, 1, and 2 hours after injections and serum was analyzed by ELISAs. Lastly for experiment 4, 14-week-old developer drakes and hens at Maple Leaf Farms were assessed for a transportation stress experiment. Blood from 10 ducks/sex/time/barn were collected at 24 hours before transport to the breeder barn, immediately after a 1-hour transport, 24 hours after, and 1 week after transport. The results from experiment 1 yielded that both cortisol and corticosterone can be measured without the presence of unwanted contaminants or other products. Experiment 2 identified the greater sensitivity of mass spectrometry when reading GC levels, although the differences were linear. Experiment 3 showed that serum corticosterone levels were significantly increased at 1 hour after ACTH injections in both drakes and hens, with levels continuing to increase for the drakes. Serum cortisol levels were significantly increased at 1 hour after ACTH injections in both sexes, however, the hens had greater levels compared to the drakes. Serum cortisol levels returned to levels similar to that of saline-injected ducks at the 2-hour mark. Lastly, the transportation stress portion showed that cortisol was released at about 1/3 of corticosterone levels in both sexes. Hens showed increased levels of serum corticosterone compared to drakes at all time points except for 1 week after transport, and also had significantly increased serum cortisol levels at all time points. In conclusion, the ELISA kits were verified for future use when measuring GC as well as mass spectrometry. GC were detected in the ACTH and transportation stress experiments with hens displaying a greater sensitivity to GC release due to increased circulating levels compared to drakes. Although it was nonsignificant, there was a trend for GC to increase in response to transport. </p> <p><br></p> <p>There are sex differences in GC release and HLR for Pekin ducks and various challenges from the studies support this. With hens showing increased sensitivity to stress and drakes with more transient and gradual levels, we have consistently seen that both GC have differential roles in the stress response and not only is it critical to study both hormones, the timing of when measurements are taken are important as well to get a clear understanding of when the stress response is initiated. </p> <p><br></p> <p>Chapter 3 went further to understand the response of GC and HLR. The objective was to  investigate the release of cortisol and corticosterone in response to an ACTH dose response challenge. In Chapter 2, only one dose of cosyntropin was used and sample collection times only went to 2 hours after injections. In this study, 2 additional doses and an extra hour of sample collection were added to obtain more information. Pekin ducks were either given IM cosyntropin injections or saline for control, with an N of 10/sex/treatment. There were 3 treatment doses: High (0.06 mg/kg), medium (0.03 mg/kg), and low (0.015 mg/kg). All injections were given promptly at 0730 hours. Blood was collected at 0, 1, 2 and 3 hours after injections from the tibia veins to obtain serum for ELISAs. Blood smears were done to analyze HLR and sent to an independent lab to obtain values. The results indicated that both GC had significant sex x dose x time interactions. The low dose injection had no effect on corticosterone in hens with a slight increase for drakes at the first hour. The high dose for hens led to a spike in corticosterone levels at the first hour with a gradual decrease, and drakes had an increase that lasted for 2 hours until they returned to baseline at the last hour. The high dose in drakes stimulated cortisol release during the first 2 hours after injection with a similar effect in hens. However, hens had elevated levels compared to drakes. Finally, there was no dose response effect for HLR, although interestingly, the low dose injection elevated HLR even though there was no effect in GC. There were sex differences in the HLR response where the drakes given the high dose had levels that plateaued by the third hour, while the hens still had elevated levels. In conclusion, the ACTH dose-response test identified that ACTH has a dose-dependent effect in both GC and sex differences in their release. HLR also showed sex differences that did not depend on the dose given.</p> <p><br></p> <p>Chapter 4 observed acute exposure of GC in ducks. Pekin ducks were assigned 10/sex/treatment to receive either IM control, cortisol, or corticosterone injections. In addition, a low-dose cortisol treatment was given to represent the endogenous levels of cortisol compared to corticosterone. The control injections contained safflower oil, which was chosen as vehicle due to the low levels of genistein present. This is important as genistein is a plant estrogen and this could interact with the GC and alter the results. Blood was collected at 0, 1, 2, and 3 hours after injections for serum analysis with ELISAs, and blood smears were collected for complete blood count (CBC) differentials. Significant sex x treatment x time interactions were notable in both GC. Hens had significant increases at the first hour after injections in all treatments compared to controls, and drakes had increases at 2 hours after injections in all treatments except the low-dose cortisol. </p> <p><br></p> <p>After observing the effect of acute stress in ducks, the next step was to investigate the effects of chronic stress in chapter 5. Adult breeder Pekin ducks were randomly distributed into 3 groups: corticosterone, cortisol, or control treatments. The GC were in crystalline steroid form distributed through 2 capsules that were subcutaneously implanted on the backs of the neck. The ducks in the control group were given empty capsules. Blood smears, blood draws for serum, egg collection, body weights, and organ samples were collected over a period of 2 weeks. For the results, the corticosterone implants elevated corticosterone levels in both sexes. Interestingly, cortisol levels were elevated in both GC treatments in both sexes. Cortisol elevated HLR in drakes 1 day after implants with no effect from corticosterone. Hens had elevated HLR from both GC at all timepoints throughout the experiment. There were no significant differences in morphometrics in either sex. Corticosterone was not present in eggs, but cortisol was elevated in the albumen on day 7 and 14 of the experiment. Overall, there were sex differences in HLR where hens had greater levels in both GC treatments.</p>

Dietary N-3 PUFA plays a key role in brain maturation, development, stress response and cognitive abilities (Weiser et al., 2016; Devarshi et al., 2019). As adolescent’s prefrontal cortex is maturating, the period becomes sensitive to external factors such as environment, nutrition, and stress (Petrovich et al., 2001; Calabro et al., 2020). In this thesis, we aim to expand our knowledge of the influence of external factors, such as dietary omega-3 supplementation and enriched environment, during this critical maturation period. By designing four distinct studies, we tested the hypothesis that visible sex-specific alterations would arise from adolescence targeted diet n-3 PUFA supplementation and enriched environment, which would act to modify physiological and stress responses, as well as socio-emotional and cognitive performance. Our first study characterized the impact n-3 PUFA and n-6 PUFA regimen on corticosterone secretion and behavioural responses in adolescent male rodents. Additionally, it assessed the effects of delivery method (gavage versus restricted feeding) during this sensitive maturation period to ensure using a method with limited stress-mediated outcomes. This study highlighted gavage to induce reduced effects on corticosterone (CORT) secretion, regardless of the provided supplementation. On the last day of feeding, CORT secretion was diminished in fish oil (FO) fed rats exposed to restricted feeding, suggesting FO diet to promote physiological adjustments. Data also demonstrated that FO and soybean (CSO) rich diets were able to reduce anxiety-like behaviour compared to a high-fat diet intake (Hydrogenated Vegetal Fat - HVF), highlighting the role of n-3 PUFA dietary supplementation during adolescence on stress regulation. Our second study assessed sex-specific impact of adolescence targeted dietary supplementation on brain Docosahexaenoic Acid (DHA), Arachidonic Acid (AA) and Linolenic acid (LA) concentrations immediately following supplementation and during adulthood. Our findings demonstrated overall elevated DHA, AA and LA brain tissue concentrations in female compared to male rats, regardless of dietary supplementation. Benefit of supplementation were most apparent in adolescent males, where FO led to higher DHA concentrations compared to soybean oil supplementation, supporting a positive influence of FO dietary supplementation in males during intensive hormonal fluctuation and brain maturation. However, adolescent male rats showed reduced ability to extract nutrient essential fatty acids compared to female counterparts. Our third study characterized sex-specific coping strategies, socioemotional responses, and glucocorticoid regulation following an n-3 PUFA rich diet and enriched environment (EE) during the adolescent period. While basal CORT secretions were not significantly altered by supplementation in males, a gradual increase in CORT was observed during supplementation, peaking at DAY21. Passive coping strategies was preferred in the FST in RC (Regular Cage)- housed females exposed to FO while RC-housed CSO-fed males opted for an active climbing coping strategy. Increase locomotion and anxiolytic behaviour were observed in CSO-supplemented males (exposed to EE), while CSO by itself promoted social recognition in males. In contrast, sociability was improved in FO EE exposed females, indicating possible synergic effects. Adulthood hippocampal GR-ir expression was reduced at the hippocampal CA3 region in FO/RC and CSO/EE rat groups, which could have influenced memory consolidation and stress resilience. Overall, results from this study provided insights on positive effects associated with short-term adolescent n-3 PUFA supplementation in females, while male appeared to most benefited from soybean diet supplementation. Our fourth and last study assessed age- and sex-dependent influences of dietary supplementation on cognitive performance in the Barnes Maze Test. Our results showcase a gradual decrease in latencies to the escape box, as well as progressive decrease in working memory errors (WME) in adult compared to adolescent rats. Over the testing period, the FO females and CSO males showed improved performance through reduction of WMEs on specific days, which could subtend sex-related effects of dietary supplementations. However, while discrete effects of n-3 PUFA were more apparent in female rats, short-term supplementation appeared insufficient to promote consistent enhancement of visuospatial performance or cognitive flexibility that could be observed throughout the testing period. In conclusion, our findings support the importance of studying single and combined factors to understand overall impact. We were able to consistently demonstrate beneficial effects on coping strategies, stress reactivity, sociability, and cognitive performance of adolescence-targeted fish oil supplementation, especially in female rodents.

No description available.

Fluoxetine and escitalopram are the only antidepressants approved by the Food and Drug Administration of the United States of America (FDA) for treatment of major depression in children and adolescents. Both drugs are selective serotonin reuptake inhibitors (SSRIs). In recent years there has been a growing concern over the long-term developmental effects of early-life exposure to SSRIs. The current study employed male Flinders Sensitive Line (FSL) rats, a well described and validated translational model of depression, to investigate the long term effects of pre-pubertal fluoxetine exposure. First we examined the effect of such early-life exposure on the development of depressive-like behaviour, locomotor activity and anxiety-like behaviour as manifested in early adulthood. Next, the current study investigated the effect of pre-pubertal fluoxetine exposure on the acute monoaminergic stress response, as displayed later in life. Animals received either saline (vehicle control), or 10 mg/kg/day fluoxetine from postnatal day (ND+) 21 to ND+34 (pre-puberty). The treatment period was chosen to coincide with a developmental phase where the serotonergic system’s neurodevelopment had been completed, yet the noradrenergic and dopaminergic systems had not, a scenario comparable to neurodevelopment in human adolescents. Both behavioural and in vivo intra-cerebral microdialysis experiments were conducted after ND+60 (early adulthood). On ND+60 rats allocated to behavioural experiments were evaluated for depressive-like behaviour in the forced swim test (FST), locomotor activity in the open field test (OFT), and anxiety-like behaviour in the OFT. Corticosterone concentrations were shown to be significantly higher in male FSL rats exposed to a 10 minute forced swim stress when compared to male FSL rats not exposed to a forced swim stress on ND+60. In the microdialysis experiments the rats were exposed to an acute 10 minute forced swim stress and the concentrations of the monoamines and their metabolites were measured before, during, and after the acute stressor. Relative to saline-treated (control) rats, fluoxetine-treated FSL rats did not show long-term changes in immobility in the FST (i.e. no anti-depressant-like activity) on ND+60. Like-wise anxiety-like behaviour in the OFT did not change. However, a significant decrease in locomotor activity was observed in fluoxetine-treated FSL rats compared to saline-treated (control) rats. These data suggest that a long-lasting anti-depressant-like effect of fluoxetine may be masked by the effect on locomotor activity. With measurements from the microdialysis experiments a significant attenuation of the noradrenergic stress response was observed in fluoxetine-treated rats compared to saline controls. A similar picture was observed for 5-hydroxyindole-3-acetic acid (5-HIAA), a metabolite of serotonin (5-HT), although the latter was not statistically significant. At baseline, before the stressor, significant increase in dopamine (DA) levels were observed in fluoxetine treated rats when compared to saline controls, suggesting that enhanced dopamine neurotransmission may comprise a long-term effect of pre-pubertal fluoxetine treatment. There were no discernible differences in homovanilllic acid (HVA) concentrations between fluoxetine-treated rats and saline controls. In conclusion significant developmental effects of pre-pubertal fluoxetine exposure were observed later in life and these findings warrant further investigation. / MPharm (Pharmacology), North-West University, Potchefstroom Campus, 2015

Fluoxetine and escitalopram are the only antidepressants approved by the Food and Drug Administration of the United States of America (FDA) for treatment of major depression in children and adolescents. Both drugs are selective serotonin reuptake inhibitors (SSRIs). In recent years there has been a growing concern over the long-term developmental effects of early-life exposure to SSRIs. The current study employed male Flinders Sensitive Line (FSL) rats, a well described and validated translational model of depression, to investigate the long term effects of pre-pubertal fluoxetine exposure. First we examined the effect of such early-life exposure on the development of depressive-like behaviour, locomotor activity and anxiety-like behaviour as manifested in early adulthood. Next, the current study investigated the effect of pre-pubertal fluoxetine exposure on the acute monoaminergic stress response, as displayed later in life. Animals received either saline (vehicle control), or 10 mg/kg/day fluoxetine from postnatal day (ND+) 21 to ND+34 (pre-puberty). The treatment period was chosen to coincide with a developmental phase where the serotonergic system’s neurodevelopment had been completed, yet the noradrenergic and dopaminergic systems had not, a scenario comparable to neurodevelopment in human adolescents. Both behavioural and in vivo intra-cerebral microdialysis experiments were conducted after ND+60 (early adulthood). On ND+60 rats allocated to behavioural experiments were evaluated for depressive-like behaviour in the forced swim test (FST), locomotor activity in the open field test (OFT), and anxiety-like behaviour in the OFT. Corticosterone concentrations were shown to be significantly higher in male FSL rats exposed to a 10 minute forced swim stress when compared to male FSL rats not exposed to a forced swim stress on ND+60. In the microdialysis experiments the rats were exposed to an acute 10 minute forced swim stress and the concentrations of the monoamines and their metabolites were measured before, during, and after the acute stressor. Relative to saline-treated (control) rats, fluoxetine-treated FSL rats did not show long-term changes in immobility in the FST (i.e. no anti-depressant-like activity) on ND+60. Like-wise anxiety-like behaviour in the OFT did not change. However, a significant decrease in locomotor activity was observed in fluoxetine-treated FSL rats compared to saline-treated (control) rats. These data suggest that a long-lasting anti-depressant-like effect of fluoxetine may be masked by the effect on locomotor activity. With measurements from the microdialysis experiments a significant attenuation of the noradrenergic stress response was observed in fluoxetine-treated rats compared to saline controls. A similar picture was observed for 5-hydroxyindole-3-acetic acid (5-HIAA), a metabolite of serotonin (5-HT), although the latter was not statistically significant. At baseline, before the stressor, significant increase in dopamine (DA) levels were observed in fluoxetine treated rats when compared to saline controls, suggesting that enhanced dopamine neurotransmission may comprise a long-term effect of pre-pubertal fluoxetine treatment. There were no discernible differences in homovanilllic acid (HVA) concentrations between fluoxetine-treated rats and saline controls. In conclusion significant developmental effects of pre-pubertal fluoxetine exposure were observed later in life and these findings warrant further investigation. / MPharm (Pharmacology), North-West University, Potchefstroom Campus, 2015

Le débit joue un rôle de première importance dans la modulation des caractéristiques physico-chimiques des rivières. Les poissons, à travers leur habitat, dépendent directement de cet ensemble de caractéristiques riveraines. De nombreuses études ont démontré qu’une altération du débit naturel des rivières, telle que par des installations hydro-électriques, a un effet négatif à l’échelle des populations et communautés de poissons. Par contre, les mécanismes qui sous-tendent ces relations sont toujours méconnus. Les processus physiologiques des poissons déterminent la façon dont ils sélectionnent leur habitat. La réponse au stress a été proposée comme étant un mécanisme qui les guide à travers les changements qui surviennent dans leur environnement. Le comportement, le cortisol plasmatique, le glucose et le lactate sanguin sont des indicateurs de la réponse au stress chez les poissons. Dans un premier temps, le mouvement de grands brochets Esox lucius L. a été observé dans deux rivières: l’une est régulée par éclusées, l’autre est non régulée et donc libre de barrage. Les résultats démontrent que le taux de mouvement chez des poissons qui habitent la rivière régulée est plus élevé que celui des poissons qui habitent dans la rivière non régulée. De plus, la direction de relation entre la distance parcourue par les poissons et le débit diffère entre rivières, et ce pour une même espèce. Dans un deuxième temps, l’effet d’une élévation de vitesse d’eau sur le cortisol, glucose et lactate de brochets qui proviennent de deux rivières qui présentent des types de gestion de débit contrastés est évalué. Ce chapitre conclut que les poissons de la rivière régulée 1) relâchent moins de glucose dans leur sang, et 2) ont des mécanismes qui permettent une accumulation moindre de lactate dans leur sang, que les poissons de la rivière non régulée lorsqu’ils sont soumis à une augmentation de vitesse d’eau. Dans un troisième temps, une approche analytique a été développée permettant de quantifier l’effet du débit sur la façon dont les brochets sélectionnent les conditions physiques de leur habitat, telle que la vitesse de l’eau. Les résultats des chapitres précédents suggèrent que les poissons de la rivière régulée sont soumis à des vitesses d’eau plus grandes que les poissons de la rivière non régulée. Ce nouvel outil permet de valider cette hypothèse. En dernier lieu, les taux de base et maximaux de cortisol plasmatique, ainsi que de glucose et lactate sanguin ont été mesurés chez des brochets qui vivent dans les deux types de rivière. Ces indicateurs témoignent de la qualité de l’habitat dans lequel les poissons vivent. Nos résultats suggèrent que les poissons qui vivent dans la rivière régulée peuvent moduler leurs niveaux de base et maximaux en cortisol plasmatique dans le but d’éviter le stress chronique. Cette thèse évalue les effets des changements de débit sur les poissons par des approches innovantes, situées à la frontière entre les domaines physiologiques et écologiques. Elle contribue à approfondir nos connaissances en ce qui a trait aux mécanismes par lesquels les poissons se distribuent à travers les différents habitats de rivière. / Flow is an important determinant of physicochemical characteristics of rivers. Fish communities in rivers are strongly dependant of their habitat, which is directly dictated by this set of characteristics. The loss of the natural flow regime, through regulation by hydroelectric facilities, for example, has the potential to directly affect the fish communities. Numerous studies have shown that the loss of natural flow regimes negatively impact fish populations and communities, but not much is known about the mechanisms that underlie such a relationship. Physiological processes determine the way that fish select their habitat. The stress response has been proposed as a mechanism that guides fish throughout the environmental changes happening in their habitat. Indicators of the fish stress response comprise behaviour, plasma cortisol, and blood glucose and lactate. First, northern pike Esox lucius L. movements were assessed in two rivers with contrasting flow regimes: a hydropeaking regulated river and an unregulated free-flowing river. Using manual tracking by radio-telemetry, we found that pike moved at a higher rate in the regulated river than in the unregulated river. Results also show that the direction of the relationship between movement of pike and flow can vary between rivers. Second, the effect of a water velocity increase on plasma cortisol, blood glucose and blood lactate levels in wild pike originating from the two rivers with contrasting flow regimes were assessed. Our results show that blood glucose and lactate concentrations are significantly diminished for fish originating from the regulated river, in comparison to fish originating from the unregulated river, following an increase in water velocity. Third, a novel analytical framework was developed that allow one to quantify the effect of the flow on fish selection of the physical conditions of their habitat (e.g. water velocity). Results obtained in the previous chapters suggest that pike living in the regulated river might be subjected to higher water velocities than fish living in the unregulated river. This novel tool will allow us to validate this hypothesis. Lastly, basal and maximum acute stress-induced concentrations in plasma cortisol, and blood glucose and lactate were quantified in pike living in both the regulated and the unregulated rivers. These physiological parameters can give an indication of the fish habitat quality. Our results suggest that fish from the regulated river are able to modulate their plasma cortisol to dampen their HPI-axis responsiveness and avoid chronic stress. This thesis assesses the effects of flow fluctuations on fish using novel approaches, situated at the intersection between the fields of physiology and ecology. It significantly contributes to broaden our knowledge of the mechanisms underlying fish habitat selection in rivers.

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