<p>Knowledge on fuel use and muscle metabolism in high altitude mammals is very limited. Yet, as the oxidation of carbohydrates offers an oxygen-saving advantage over the oxidation of fatty acids (15-30% more energy produced per oxygen used), one possible adaptation to maintain performance at high altitude is to elevate the use of carbohydrates as a fuel source for energy metabolism. To test this hypothesis, I performed intraspecific and interspecific comparisons of whole-body fuel use and muscle metabolism in closely related high (4000-4500 m) and low altitude (100-300 m) native mice (genus <em>Phyllotis</em>), which I collected at different locations in Andean and coastal regions of Peru. My results show a higher proportional use of carbohydrates when oxygen becomes limited in high altitude <em>Phyllotis</em> in comparison to their low altitude counterparts. This phenotype does not seem to result from similar phylogenetic history or from a chronic exposure to hypobaric hypoxia during development or adulthood. Accordingly, this thesis provides the first compelling evidence of enhanced carbohydrate utilization as an adaptation to high altitude, a hypothesis proposed nearly 30 years ago. The mechanisms responsible for this shift in fuel use are unknown. There were no strong indications of a greater capacity for carbohydrate oxidation in skeletal and cardiac muscles of high altitude <em>Phyllotis</em> mice. Finally, as this thesis provides the first report of whole-body fuel use in mice, a comparison with other mammalian species (rats, dogs and goats) revealed that the current model of mammalian fuel selection, which is thought to be conserved among mammals, does not apply to small mammals. I thus revisited the current model and proposed a new one general to all mammals. This thesis thus provides significant advancements not only in the field of high altitude physiology but also in the field of mammalian energetics.</p> / Doctor of Philosophy (PhD)

<p>Under hypoxia mammals face many challenges, especially in terms of energy production. To conserve O2, mammals may enter a hypometabolic state or rely more heavily on anaerobic metabolism. However, the latter strategy is not a viable option during chronic hypoxia and other cellular changes are needed. Under chronic hypoxia, mammals have been predicted to alter their metabolic machinery in an attempt to increase the efficiency of ATP production to reduce the amount of O2 used by the mitochondria. One way efficiency is believed to increase is through a change in the composition of cytochrome c oxidase (COX). Cell culture experiments have shown a decrease in the COX4-1 isoform and an increase in the COX4-2 isoform under hypoxia, leading to an increase in the reaction efficiency of COX. In the present study, I observed an increase in the mRNA levels of COX4-2 after 24hrs of hypoxia. However, this change was not mirrored by corresponding changes at the protein level. Further, I examined the phosphorylation state of pyruvate dehydrogenase (PDH) as an indicator of PDH activity. Under chronic hypoxia resting mice exhibited a significant rise in PDH phosphorylation. This increase may represent a decrease in PDH activity and a decreased reliance on carbohydrate derived acetyl-CoA.</p> <p>I also explored the effects plastic changes in muscle during chronic hypoxia had on muscle metabolism during acute exercise. In hypoxic post-exercise mice, a significant increase in muscle lactate levels was observed compared to rest. This rise was not present in control mice, suggesting that acclimated mice were relying more heavily on anaerobic metabolism. However, there were no significant changes in PDH phosphorylation in post-exercise mice which could help to explain elevated muscle lactate levels.</p> / Master of Science (MSc)

Variations in skeletal morphology have often been used to interpret an organism’s overall activity level when direct observation is not possible. Although skeletal change in response to exercise is well documented, the skeleton’s response to mechanical loading is modulated by several factors (e.g. age, hormones, sex). Additionally, variation in skeletal morphology is partially a result of genetic variation, which is rarely accounted for in inferences of locomotor activity from skeletal remains. However, blood flow to long bones serves as a proxy for bone metabolic activity, which can be used to infer locomotor activity. Long bones receive blood from three sources, with the nutrient artery supplying the bulk of total blood volume in mammals (50-70%). The size of the nutrient artery can be estimated from the dimensions of the nutrient canal, which is present long after the vascular tissue has degenerated. The literature on nutrient canals is sparse, with most studies consisting of anatomical descriptions from surgical proceedings, and only a few studies investigating the links between nutrient canals and physiology or behavior. Moreover, no study to date has accurately modelled the size and shape of the nutrient canal. For this study, mice from an artificial selection experiment for high voluntary wheel-running behavior were used. High Runner mice from the experiment are known to differ in both metabolic and locomotor activity, with mice from HR lines having increased VO2max and increased voluntary wheel-running behavior when compared to controls. 137 femora from mice of the 11th generation of this selection experiment were µCT scanned. Three-dimensional reconstructions of nutrient canals were measured for minimum cross-sectional area (an index of blood flow). Nutrient canals varied far more in number and shape than prior descriptions would indicate. Canals adopted non-linear shape and pathing as they traversed from the periosteum to the medullary cavity, occasionally even branching within the cortical bone. Additionally, mice from both HR and control lines had more than four nutrient canals per femur. Mice from HR lines had significantly larger nutrient canal area than controls, which was not the result of an increase in the number of nutrient canals, but rather an increase in their average size. This study demonstrates that mice with an evolutionary history of increased locomotor activity and metabolic rate have a concomitant increase in the size of their nutrient canals.

Early exposure to hypoxia is related to a variety of physiological and metabolic changes that have lasting effects on organisms’ physiology and life history. We measured the effects of maternal and embryonic mild, intermittent hypoxia on the life history of four clones of microcrustacean Daphnia magna, an emerging model organism for the studies of senescence and longevity. Daphnia individuals were produced parthenogenically, maintained in individual vials, and fed standard algal concentration daily. The cohort consisted of 189 individuals. We measured body size at first reproduction, fecundity (including late-life fecundity peak), offspring sex ratio, and longevity. We found no effect of maternal and embryonic hypoxia on body size and longevity; however, there was a slight but statistically significant increase in age-specific mortality in the early hypoxia treatment cohort. Daphnia from the hypoxia group showed higher early fecundity which disappeared by the age of 100 days. A late-life spike in fecundity was observed at the age of 100 days when hypoxia group individuals showed significantly lower fecundity. There was little evidence of a trade-off between early- and late-life fecundity. Finally, early hypoxia affected mid-life male production in one of the four clones, and we discuss possible physiological changes triggered by maternal and embryonic exposure to hypoxia.

<p>Mosquitoes pose significant threats to human health because they act as vectors for disease causing viruses and protozoans. Indeed, <em>Aedes aegypti</em> is known as the Yellow Fever Mosquito because of its role as a vector for viral infections that kill thousands of people each year. A more thorough understanding of mosquito physiology will aid development of novel control strategies. Previous work on ion transport across the midgut has been focused primarily on larval <em>A. aegypti</em>, while research on the midgut of the adult stage is less complete. The posterior midgut of the adult female is of particular interest because it is used for the storage and digestion of the blood meal which is required for the production of eggs. This study used an array of electrophysiological methodologies such as the Scanning Ion Electrode Technique (SIET) in order to elucidate the patterns and mechanisms of Na⁺, H⁺ and K⁺ transport across the posterior midgut at intervals during postprandial diuresis and digestion of the blood meal. Measurements of transepithelial potential indicated that the lumen was at its most negative (-13.2 mV) three hours after the blood meal and then gradually became less negative during the time course of digestion. Na⁺ was absorbed (from lumen to bath) at all intervals after the blood meal (6 min, 30 min, 2h, 24 h); calculations of the electrochemical potential indicated that absorption required active transport. H⁺ absorption at all times (6 min – 48 h) after the blood meal was also active (<em>i.e.</em> against the electrochemical gradient for H⁺) and was greatly reduced by inhibition of carbonic anhydrase. K⁺ transport across the midgut exhibited two distinct phases. During diuresis, luminal concentrations of K⁺ were in the range 24 – 28 mM and secretion into the midgut was opposed by the electrochemical gradient, indicating active transport. After diuresis, during blood meal digestion, concentrations of K⁺ in the midgut contents were high (95 – 134 mM) and absorption of K⁺ was favoured by the electrochemical gradient. K⁺ absorption was sensitive to the channel blocker Ba²⁺ during this period.</p> / Master of Science (MSc)

Bats are the only mammals capable of powered flight. In flight, bats consume up to 20 times more oxygen per hour than under basal conditions. This is twice the increase reported for running mammals of the same body sizes. Birds are the only other group of vertebrate capable of powered flight. By plotting morphological and physiological parameters against body mass for bats, terrestrial mammals, and birds, we can observe to what extent these parameters permit high rates of oxygen delivery necessary for flight. In this study we analyzed basal metabolic rate, heart mass, and hematocrit, and compared how differently they scale in the afore-mentioned groups. We found that larger heart masses are associated with the ability to fly; hematocrit values for birds change markedly with body size, while those for mammals and bats are nearly independent of body size; and that BMR scales differently in all three groups.

Tropidolaemus wagleri is a species of Asian pitviper with a geographic range including Thailand, Vietnam, Malaysia, Singapore, Bruniei, parts of Indonesia, and the hilippines. Tropidolaemus is a member of the Crotalinae subfamily, within Viperidae. The genus Tropidolaemus includes five species, and was once included within the genus Trimeresurus. While some osteologic characteristics have been noted a comprehensive description of cranial elements has not been produced for T. wagleri. An in-depth description of the cranial skeleton of Tropidolaemus wagleri lays the foundation for future projects to compare and contrast other taxa within Crotalinae and Viperidae. The chosen reference specimen was compared to the presumed younger specimens to note any variation in ontogeny. The study here provides a comprehensive description of isolated cranial elements as well as a description of ontogenetic change within the specimens observed. This study contributes to the knowledge of osteological characters in T. wagleri and provides a foundation for a long term project to identify isolated elements in the fossil record.

Sleep is a fundamental and essential component of vertebrate life, although its exact function remains unknown. Animals that are deprived of sleep typically show reduced neurobiological performance, health, and in some cases, survival. However, a number of animals exhibit adaptations that permit them to carry out normal activities even when sleep is restricted or deprived. Lapland longspurs (Calcarius lapponicus), arctic-breeding passerine birds, exhibit around-the-clock activity during their short breeding season, with an inactive period of only 3–4 h/day (71°N). Whether these birds suffer behavioral and physiological costs associated with acute sleep loss (SL) is unknown. To assess the effects of SL, wild-caught male longspurs were placed in captivity (12L:12D) and trained for 2 months using a series of memory tests, including color association and spatial learning to assess executive function. Birds were then placed in automated sleep fragmentation cages that utilize a moving wire to force movement every 1 min (60 arousals/h) during 12D (inactive period) or control conditions (during 12L; active period). After a single round of SL (or control) treatment, color association and spatial learning tests were conducted. Baseline plasma corticosterone concentration, body mass, and satiety were also assessed. SL significantly elevated corticosterone levels and increased accuracy during the color association test, but not the overall time required to complete the test. SL had no effect upon spatial learning, body mass, or satiety. Taken together, these results suggest that Lapland longspurs exhibit a behavioral, but not a physiological, resilience to acute SL.

Xylem vessels have long been proposed as a key innovation for the ecological diversification of angiosperms by providing a breakthrough in hydraulic efficiency to support high rates of photosynthesis and growth. However, recent studies demonstrated that angiosperm woods with structurally ‘primitive’ vessels did not have greater whole stem hydraulic capacities as compared to vesselless angiosperms. As an alternative to the hydraulic superiority hypothesis, the heteroxylly hypothesis proposes that subtle hydraulic efficiencies of primitive vessels over tracheids enabled new directions of functional specialization in the wood. However, the functional properties of early heteroxyllous wood remain unknown. We selected the two species of Canellales from Madagascar to test the heteroxylly hypothesis because Canellaceae (represented by Cinnamosma madagascariensis) produces wood with vessels of an ancestral form, while Winteraceae, the sister-clade (represented by Takhtajania perrieri) is vesselless. We found that heteroxylly correlated with increased wood functional diversity related mostly to biomechanical specialization. However, vessels were not associated with greater stem hydraulic efficiency or increased shoot hydraulic capacity. Our results support the heteroxylly hypothesis and highlight the importance integrating a broader ecological context to understand the evolution of vessels.

Xylem vessels have long been proposed as a key innovation for the ecological diversification of angiosperms by providing a breakthrough in hydraulic efficiency to support high rates of photosynthesis and growth. However, recent studies demonstrated that angiosperm woods with structurally ‘primitive’ vessels did not have greater whole stem hydraulic capacities as compared to vesselless angiosperms. As an alternative to the hydraulic superiority hypothesis, the heteroxylly hypothesis proposes that subtle hydraulic efficiencies of primitive vessels over tracheids enabled new directions of functional specialization in the wood. However, the functional properties of early heteroxyllous wood remain unknown. We selected the two species of Canellales from Madagascar to test the heteroxylly hypothesis because Canellaceae (represented by <em>Cinnamosma madagascariensis</em>) produces wood with vessels of an ancestral form, while Winteraceae, the sister-clade (represented by <em>Takhtajania perrieri</em>) is vesselless. We found that heteroxylly correlated with increased wood functional diversity related mostly to biomechanical specialization. However, vessels were not associated with greater stem hydraulic efficiency or increased shoot hydraulic capacity. Our results support the heteroxylly hypothesis and highlight the importance integrating a broader ecological context to understand the evolution of vessels.