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Arctic food webs are characterized by multi-year predator-prey cycles. Arctic foxes (Vulpes lagopus) feed primarily on rodents, but also on avian and marine prey when rodents are scarce. I examined temporal variation in the arctic fox diet related to food availability and stress hormones (i.e. cortisol). Lemmings (Dicrostonyx richardsoni), goslings, and goose eggs were important components of the fall and winter diet. Goslings were important in fall, even when rodents were abundant. Lemmings were most important in winter, even when lemming densities were low. Consuming stored eggs did not reduce cortisol concentrations, suggesting that arctic foxes do not prefer stored eggs to lemmings. I also found that prey hormones increased fecal hormone concentrations of captive arctic foxes, introducing an additional caution for hormone studies involving predators. Nonetheless, relationships between stress hormone concentrations and changes in food availability can provide insight regarding the importance of food sources to consumer populations.

The skin of many fishes contains large epidermal club cells (ECCs) that are known to release chemicals (alarm cues) that warn other fishes of danger. Initial research on ECCs focussed on their role in predator avoidance behaviour, however later research revealed that these cells might also have immune functions. Anthropogenic activities have dramatically increased over the past decades, with the consequence that many organisms simultaneously get exposed to multiple environmental stressors. We have seen considerable reductions in stratospheric ozone with a concomitant increase in global ultraviolet radiation (UVR). Metal pollution associated with industrial activity is also increasing on a global scale. Cadmium (Cd) is one such ubiquitous pollutant which is known to be toxic to organisms at extremely low concentrations. The main goal of my PhD research was to understand how multiple environmental stressors play a role in altering ECC investment and chemically-mediated predator-prey interactions by indirectly elucidating the evolutionary role of ECCs. The first experiment investigated the effects of in vivo ultraviolet radiation (UVR) exposure on ECC investment, physiological stress responses and potency of alarm cues in fathead minnows (Pimephales promelas). Subsequently, I investigated the interactive effects of UVR and/or waterborne cadmium (Cd) exposure using the same end points. I found that minnows exposed to UVR, either in the presence or absence of Cd, showed consistent decrease in ECC investment compared to non-exposed controls. There was a significant increase in cortisol levels of UVR exposed minnows compared to unexposed minnows. However, the combined exposure of UVR and Cd reduced cortisol levels relative to that in UVR only exposure. Surprisingly, there was no difference in the potency of the cues prepared from the skin of UVR and/or Cd exposed or non-exposed fish indicating that UVR and/or Cd exposure combined may have little influence on chemically-mediated predator-prey interactions. In aquatic systems, much of the negative effects of UVR are minimized by dissolved organic carbon (DOC) which is known to attenuate rates of UVR across the water column. In my third study, I investigated if DOC played a role in ameliorating the effects of in vivo UVR exposure on physiological stress and ECC investment in fathead minnows. I used two sources of DOC, a commercial soil based DOC (Sigma Aldrich Humic Acid) and a terrigenous source of DOC (Luther Marsh Natural Organic Matter). I found that fish exposed to UVR, in the presence of either source of DOC, in the presence and absence of UV blocking filter, maintained high ECC investment and reduced cortisol levels compared to fish exposed to UVR only. Studies that have examined factors that influence ECC investment have often been hampered by large variation in baseline levels of ECC. The larger the baseline variation in ECC number, the more difficult it is to elucidate factors responsible for changes in ECC investment. While I did not find this problematic in my work with UVR and Cd, others have failed to find effects in manipulative experiments. Consequently, my fourth study examined between and within variation in ECC investment across multiple sites in Saskatchewan and tried to investigate if holding fish under controlled laboratory conditions for up to 28 days would help reduce variation in ECC investment between and within populations. I found some evidence that I could reduce within population variation in ECC investment through time, but could not reduce among-population variation in mean ECC investment.

In contrast to most teleost fish that are ammoniotelic, the gulf toadfish (Opsanus beta) is both facultatively ureogenic and ureotelic. In vivo pharmacological manipulations were used to show that lowering circulating cortisol levels or blocking glucocorticoid receptors (GR) enhanced both urea excretion and urea pulse size. These findings demonstrated that changes in pulsatile urea excretion in the toadfish are mediated by the permissive action of cortisol through GRs. Measurement of urea transport across isolated basolateral gill membranes revealed a cortisol-sensitive carrier mechanism. Cortisol infusion in vivo significantly reduced urea transport capacity, suggesting that cortisol inhibits the recruitment of urea transport proteins (UT) to the basolateral membrane to ultimately decrease the size of the urea pulse in toadfish. A 1.2 kb fragment of the upstream transcription start site for the toadfish urea transporter (tUT) gene was isolated and in silico analysis revealed the presence of several putative glucocorticoid response element (GRE) half sites. Toadfish provided with this regulatory sequence in a reporter gene construct showed increased reporter gene transcription driven by cortisol. The data indicated that cortisol-mediated upregulation of tUT mRNA by GREs may be necessary to maintain tUT activity. Four Rhesus (Rh) glycoproteins (Rhag, Rhbg, Rhcg1, Rhcg2) were isolated from toadfish; these sequences grouped with those of other vertebrates coding for membrane channels that transport ammonia. In vivo increases in circulating cortisol reduced branchial Rh glycoprotein expression and decreased ammonia excretion. These changes were accompanied by cortisol-induced increases in glutamine synthetase activity, an enzyme that captures ammonia for urea synthesis. Taken together, the data indicated that cortisol reduces the loss by branchial excretion of ammonia, instead favouring biochemical pathways that convert ammonia to urea. This thesis confirms that nitrogen excretion in toadfish is controlled and regulated in fashions unlike those in other teleosts. The results demonstrate the importance of the GR signaling pathway in mediating changes in both urea and ammonia transport through molecular mechanisms. As a whole, the data provide a new understanding of branchial nitrogen excretion in the gulf toadfish and enhance our evolutionary perspective of the integrated biological systems involved in nitrogen excretion in fish.

The daughters of women with a history of depression are at heightened risk for a range of mental health problems. The present study investigated emotion regulation, cortisol reactivity to stress, and interpersonal competence as potential indicators of risk in adolescent girls at high versus low risk for depression. Participants were a community sample of 47 girls and their mothers (27 high risk and 20 low risk). Mothers and daughters had been interviewed to assess diagnostic history as part of a previous longitudinal study. In the current study, daughters completed the Trier Social Stress Test for Children (TSST-C) and cortisol samples were collected before and after exposure to this psychosocial stressor. Both mothers and daughters completed self-report questionnaires and daughters were re-assessed using the Depressive Disorders module of the Kiddie Schedule for Affective Disorders and Schizophrenia. High risk mothers were also interviewed to assess the timing and chronicity of their depressive episodes during their daughters’ lifetime. High and low risk girls had equivalent ratings of self-reported stress following the TSST-C, but different physiological responses. Girls at high risk for depression showed a blunted cortisol response to the TSST-C whereas low risk girls showed a normal cortisol response. High risk status for depression predicted a blunted cortisol response to stress, which predicted difficulties with emotion regulation; difficulties with emotion regulation in turn predicted a greater number of self-reported depressive symptoms. These results suggest that maternal depression may act as a stressor that compromises stress-response system functioning in daughters and produces related difficulties with emotion regulation.

Chronic major depressive disorder (CMDD) is a common and debilitating illness. Its pathophysiology needs further elucidation, before more effective targeted treatments can be developed for this condition. To gain a better understanding of the psychobiology of CMDD, three interconnected studies were conducted that examined the interplay between chronic depression, cortisol responses, and personality. Study 1 examined cortisol responses to the Trier Social Stress Test (TSST) in CMDD participants (n=29) as compared to healthy controls (n=28). It was hypothesized that cortisol responses would be greater in the CMDD population. Results indicated that females with CMDD had increased cortisol output compared to female controls, a pattern consistent with the hypothesis. However, males with CMDD had decreased cortisol responses compared to male controls. These results suggest that cortisol responses to social stress are altered in those with CMDD; however, females and males experience fundamentally different changes. Study 2 examined moderating effects of personality on cortisol responses to the TSST in those with CMDD (n=51) as compared to healthy controls (n=57). It was hypothesized that higher neuroticism and/or lower extraversion would be associated with increased cortisol responses in CMDD participants. As hypothesized, lower extraversion was associated with increased cortisol reactivity in those with CMDD but not in healthy controls. However, no association was found between neuroticism and cortisol responses. These findings could support the notion that lower extraversion is a vulnerability marker for chronic depression and thus a possible target for treatment. Study 3, evaluated the cortisol awakening response (CAR) in CMDD participants (n=27) compared to healthy controls (n=30). It was hypothesized that such awakening responses would be more pronounced in the depressed population compared to controls. Contrary to expectation, no differences were found between the groups. However, lower extraversion was associated with a lower CAR in both CMDD and healthy controls, a finding that was not anticipated a priori. These interconnected studies suggest that examining relationships between depression, cortisol responses, and personality, can assist with identifying distinct psychobiological profiles in those with chronic depression. It is proposed that this strategy will improve the likelihood of developing more targeted treatments for this population.

Chronic major depressive disorder (CMDD) is a common and debilitating illness. Its pathophysiology needs further elucidation, before more effective targeted treatments can be developed for this condition. To gain a better understanding of the psychobiology of CMDD, three interconnected studies were conducted that examined the interplay between chronic depression, cortisol responses, and personality. Study 1 examined cortisol responses to the Trier Social Stress Test (TSST) in CMDD participants (n=29) as compared to healthy controls (n=28). It was hypothesized that cortisol responses would be greater in the CMDD population. Results indicated that females with CMDD had increased cortisol output compared to female controls, a pattern consistent with the hypothesis. However, males with CMDD had decreased cortisol responses compared to male controls. These results suggest that cortisol responses to social stress are altered in those with CMDD; however, females and males experience fundamentally different changes. Study 2 examined moderating effects of personality on cortisol responses to the TSST in those with CMDD (n=51) as compared to healthy controls (n=57). It was hypothesized that higher neuroticism and/or lower extraversion would be associated with increased cortisol responses in CMDD participants. As hypothesized, lower extraversion was associated with increased cortisol reactivity in those with CMDD but not in healthy controls. However, no association was found between neuroticism and cortisol responses. These findings could support the notion that lower extraversion is a vulnerability marker for chronic depression and thus a possible target for treatment. Study 3, evaluated the cortisol awakening response (CAR) in CMDD participants (n=27) compared to healthy controls (n=30). It was hypothesized that such awakening responses would be more pronounced in the depressed population compared to controls. Contrary to expectation, no differences were found between the groups. However, lower extraversion was associated with a lower CAR in both CMDD and healthy controls, a finding that was not anticipated a priori. These interconnected studies suggest that examining relationships between depression, cortisol responses, and personality, can assist with identifying distinct psychobiological profiles in those with chronic depression. It is proposed that this strategy will improve the likelihood of developing more targeted treatments for this population.

At the cellular level, the stress response involves the synthesis of a highly conserved family of heat shock proteins (Hsps). These proteins are essential for maintenance of cellular homeostasis, both in times of stress and in normal cell functioning. Some of the most abundant forms of Hsps in the cell are members of the 70 kDa family. Intracellular heat shock protein 70 (Hsp70) expression in response to proteotoxicity is a highly conserved cellular stress response, but little is known about the role of extracellular Hsp70 (eHsp70) in fish. In order to begin characterizing eHsp70 in fish, the hypothesis that an acute stressor will elevate plasma Hsp70 levels in rainbow trout (Oncorhynchus mykiss) was tested. Subsequent in vitro studies examined whether eHsp70 level was modulated by cortisol and if this involved the action of the glucocorticoid receptor (GR), a ligand-activated transcription factor. The effect of cortisol on the eHsp70 response is important to consider because this steroid is elevated as a result of stressor exposure to allow for short-term allocation of energy stores to cope with stress. Cortisol is the primary corticosteroid in fish and exerts its main effects by binding to either GR or mineralocorticoid receptors (MR). Furthermore, eHsp70 has been previously implicated as having important immunoregulatory roles in mammalian models, but nothing has yet been reported in fish. To this end, a hypothesis tested here was that eHsp70 levels will increase after exposure to the bacterial endotoxin lipopolysaccharide (LPS), and that this response is modulated by cortisol. Finally, research on the effects of exogenous Hsp70 has not been reported in lower vertebrates; however, the relevance of this protein in intercellular signaling, especially in regards to immune regulation, is gaining increasing importance in mammalian models. Therefore, an experiment to determine whether Hsp70 would elicit upregulation of key immunoregulatory cytokines was also conducted. To accurately measure the low levels of Hsp70 in the plasma, a competitive antibody-capture enzyme-linked immunosorbent assay (ELISA) was developed. In the in vivo study, fish exposed to an acute heat shock (1h at 10°C above ambient temperature) exhibited a significant elevation in red blood cell Hsp70 levels over a 24 h period. There was also a significant increase in plasma Hsp70 levels at 4 h, but not at 24 h post-heat shock. To more specifically determine how cortisol affected the release of Hsp70, in vitro studies using primary cultures of hepatocytes demonstrated that cortisol significantly decreased eHsp70 levels in the medium at 24 h when compared with untreated controls, and this response was abolished in the presence of a GR antagonist, mifepristone (RU486). This result for the first time established a link between cortisol signaling and eHsp70 release in any animal model. When hepatocytes were exposed to LPS in vitro, eHsp70 levels were significantly lower in the LPS (30 µg/ml) group; however, heat shock abolished this effect at 24 h. Though eHsp70 levels in the heat shocked hepatocytes treated with low-dose LPS (10 µg/ml) was similar to untreated control levels, high-dose LPS treated hepatocytes showed significant elevation of eHsp70 levels above the low dose group. The ability of LPS to modulate eHsp70 release was not observed to be further regulated by cortisol. While this work suggests the modulation of eHsp70 by LPS, the physiological role remains to be elucidated. Finally when hepatocytes were exposed to exogenous Hsp70, there was no effect on key immunoregulatory genes (IL-1β and IL-8) transcript levels; however, the effect of this protein remains to be tested using other cell systems, including immune cells in fish. Overall, eHsp70 concentration was measured in trout plasma using a competitive ELISA and demonstrates for the first time that stressor exposure affects plasma eHsp70 levels in fish. Furthermore, cortisol, the primary corticosteroid in teleosts, modulates eHsp70 release in trout hepatocytes and this is action is mediated by GR signaling. Also, while trout hepatocytes secrete eHsp70 in response to endotoxin shock, a role for eHsp70 in eliciting an immune response is not clear in lower vertebrates. Taken together the results from this study suggest a role for eHsp70 in acute stress adaptation in fish, but the target tissues involved and the physiological responses remain to be elucidated. Further work on the effects of eHsp70 on target tissues effects, and the mechanisms involved, may have important implications in our understanding of the role of this stress protein in cell signaling and stress adaptation in fish.

This thesis contributes to the growing body of gender-specific health research by integrating both psychological and neuroendocrine data to assess the impacts of stress and violence on women's health. Women seeking support for intimate partner violence (IPV) were compared with women seeking support for non-interpersonal stressors (stress associated with immigration). Psychological measures included perceived stress and entrapment and mental defeat (EMD) scores as well as assessment of Axis I disorders. Neuroendocrine measures included basal levels of salivary cortisol and percent suppression of cortisol after the low-dose dexamethasone suppression test (DST). Positive relationships were found between experiences of IPV and perceived stress, EMD and Axis I diagnosis. The neuroendocrine measures did not differentiate IPV from non-interpersonal stressors and both groups showed hypersuppression of cortisol after the DST. IPV influences women's perceptions about EMD and perceived stress. By integrating neuroendocrine and psychological measures, further development of gender-specific stress models may occur.

Despite the controversy over environmental sustainability, salmon aquaculture in British Columbia is economically important for many coastal communities and is reported as being the largest agricultural export product for the province. This thesis examined the welfare status of commercially produced Atlantic salmon smolts during transport from freshwater farms to the saltwater net pens using physiology and behaviour to assess transport stress. Smolts were transported first by truck from the freshwater farm to the dock, and then in the flow-through cargo holds of a live-haul vessel to the saltwater net pens. Fish and water were sampled before and after truck transport, and several times aboard the vessel. Assessment of stress was based on measurement of plasma cortisol, glucose, lactate, potassium, sodium and chloride concentrations, as well as behavioural observations made on underwater video footage. Seven transports of fish originating from two different hatcheries were sampled; one was a land-based tank hatchery that required a 30-min drive to the dock, and the other a lake net pen facility that was 90 min to the dock. Analysis of plasma constituents supported previous studies that recovery from the stress accumulated during loading and truck transport can be quite rapid in a live-haul vessel. Underwater video footage, recorded at the freshwater farms and in the cargo holds of the Sterling Carrier, also suggested recovery onboard in that for the most part, behaviour onboard was similar to behaviour at the freshwater farms. There were some significant differences between fish from the two types of hatcheries, particularly in the original hatchery conditions and in their behavioural responses to transport conditions; however, post-transport growth and mortality rates reported by the saltwater farms showed no significant difference. Although fish were subjected to moderately stressful conditions during part of the process, smolt transport as currently carried out by our industry partners reflects good husbandry practices and fish welfare.