Graduate Theses & Dissertations

Comparison of Dehydration Techniques for Acute Weight Management in Rowing
Mild sauna dehydration and fluid abstinence were investigated as weight loss strategies for lightweight rowers. Rowers (N=12) performed a power test, an incremental VO2max test, and a visuomotor battery: once euhydrated, once following sauna dehydration (SAU), and once following fluid abstinence and then sauna dehydration (FA). The percent body mass change (%BMC) achieved, %BMC attributable to sauna dehydration, and %BMC attributable to fluid abstinence were used within linear mixed effects models to predict hydration and performance variables. Sauna and overnight dehydration exerted indistinguishable effects on plasma osmolality, urine osmolality and thirst (p > .05). Fluid abstinence but not sauna dehydration was related to lower power production on the power test (b = 12.14W / 1%BMC, FA = 673.46 ± 79.50, SAU = 683.33 ± 72.08, p = .029), a lower total wattage produced on the incremental VO2max test (b = 4261.51W / 1%BMC, FA = 71029.58 ± 16256.56, SAU = 74001.50 ± 14936.56, p = .006), lower wattages at 2 mmol/L (b = 27.84W / 1%BMC, FA = 180.74 ± 40.27, SAU = 190.82 ± 50.79, p < .001) and 4 mmol/L (b = 20.45W / 1%BMC, FA = 221.90 ± 52.62, SAU = 238.89 ± 40.78, p = .002) blood lactate, and slower movement time on a visuomotor task (b = -38.06ms / 1%BMC, p = .004). Mild fluid abstinence but not sauna dehydration reduces rowing performance when two-hour rehydration is allowed. Author Keywords: crew, fluid, hydration, lightweight, sauna, weight
role of corticosterone in breeding effort and reproductive success in tree swallows
Glucocorticoids (e.g., corticosterone (CORT)) are hypothesized to mediate decisions regarding reproductive investment during breeding, but the directionality of the relationship is not clear. The CORT-fitness hypothesis posits that high levels of CORT arise from challenging environmental conditions in which an individual will conserve resources for future reproduction or self-maintenance, and thus result in lower reproductive success (a negative relationship). In contrast, the CORT-adaptation hypothesis suggests that, during energetically demanding periods, CORT will mediate physiological or behavioural changes that result in increased reproductive investment and success (a positive relationship). Inconsistencies arise due to the various species and life-history stages studied, and the complex interactions between fitness and glucocorticoids. Using an experimental approach, I investigated the relationship between CORT and reproductive success by manipulating baseline CORT levels in female tree swallows Tachycineta bicolor prior to laying using silastic implants. Implants failed to raise CORT levels of females during either incubation or the nestling stage, and maternal treatment had no effect on indices of fitness at either stage. Using a correlative approach, partial support for the CORT-adaptation hypothesis was found: There was a positive relationship between CORT and hatching success. This only occurred when CORT was measured during incubation, when baseline CORT levels may stimulate increased reproductive effort and success. In contrast, during the nestling stage baseline CORT levels were not related to reproductive investment or success. Maternal CORT levels during incubation also did not influence nestling phenotype, although nestling stress CORT levels were higher in individuals that survived to fledging. In conclusion, CORT mediates reproductive effort and success during some breeding stages, but it is still unclear why this is the case and whether this same pattern will prevail in other contexts. Author Keywords: corticosterone, HPA axis, maternal effects, reproductive success, tree swallow

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2009 - 2029
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