abstract: Conditions during development can shape the expression of traits at adulthood, a phenomenon called developmental plasticity. In this context, factors such as nutrition or health state during development can affect current and subsequent physiology, body size, brain structure, ornamentation, and behavior. However, many of the links between developmental and adult phenotype are poorly understood. I performed a series of experiments using a common molecular currency - carotenoid pigments - to track somatic and reproductive investments through development and into adulthood. Carotenoids are red, orange, or yellow pigments that: (a) animals must acquire from their diets, (b) can be physiologically beneficial, acting as antioxidants or immunostimulants, and (c) color the sexually attractive features (e.g., feathers, scales) of many animals. I studied how carotenoid nutrition and immune challenges during ontogeny impacted ornamental coloration and immune function of adult male mallard ducks (Anas platyrhynchos). Male mallards use carotenoids to pigment their yellow beak, and males with more beaks that are more yellow are preferred as mates, have increased immune function, and have higher quality sperm. In my dissertation work, I established a natural context for the role that carotenoids and body condition play in the formation of the adult phenotype and examined how early-life experiences, including immune challenges and dietary access to carotenoids, affect adult immune function and ornamental coloration. Evidence from mallard ducklings in the field showed that variation in circulating carotenoid levels at hatch are likely driven by maternal allocation of carotenoids, but that carotenoid physiology shifts during the subsequent few weeks to reflect individual foraging habits. In the lab, adult beak color expression and immune function were more tightly correlated with body condition during growth than body condition during subsequent stages of development or adulthood. Immune challenges during development affected adult immune function and interacted with carotenoid physiology during adulthood, but did not affect adult beak coloration. Dietary access to carotenoids during development, but not adulthood, also affected adult immune function. Taken together, these results highlight the importance of the developmental stage in shaping certain survival-related traits (i.e., immune function), and lead to further questions regarding the development of ornamental traits. / Dissertation/Thesis / Ph.D. Biology 2012

When dabbling ducks are involuntarily submerged, arterial vasoconstriction produces a large increase in the peripheral resistance to blood flow which is balanced by a decrease in output of the heart, and arterial blood pressure is maintained. Arterial baroreceptors sense systemic blood pressure, and provide the afferent information to the baroreflex for pressure regulation. The effector limbs of the baroreflex are the same as those involved in the diving responses, and the baroreceptors are likely to be important in the integration of the cardiovascular responses to diving. The purpose of this study was to investigate the role of the arterial baroreceptors in maintaining blood pressure during diving, and in the initiation and maintenance of the diving responses. Baroreceptor function was studied by diving ducks at various times after barodenervation, and by electrically stimulating the central end of one baroreceptor nerve in baroreceptor-denervated animals to simulate a controlled baroreceptor input before and during submersion. Intact baroreceptor innervation was not necessary for the development of peripheral vasoconstriction, but loss of the baroreceptors modified the cardiac response to submersion by impairing the vagally mediated bradycardia. There was no effect of baroreceptor nerve stimulation on peripheral resistance during diving, and the baroreflex operated via the heart rate in modulating blood pressure early in the dive. Later in the dive, stimulation was ineffective in altering either heart rate or blood pressue. Strong chemoreceptor drive results from decreased blood oxygen and increased carbon dioxide levels in the dive, and the results of experiments to determine the mechanism of baroreflex attenuation showed that an interaction between chemoreceptor and baroreceptor inputs may be at least partly responsible for reducing baroreflex effectiveness. The main conclusion from this work is that the arterial baroreceptors contribute to the diving responses through modulation of heart rate, to help balance the fall in cardiac output against the baroreceptor-independent peripheral vasoconstriction in the first minute of forced dives. / Science, Faculty of / Zoology, Department of / Graduate

Nest success of dabbling ducks in the Prairie Pothole region of North America has been declining for the past 40 years in parallel with declines in duck populations. Low nest success seems to result from the combination of an extremely fragmented breeding ground in a human-dominated landscape with an abundant and expanding ii community of generalist nest predators. Studies that examined variables associated with nest vulnerability to predation have produced contradictory results, likely because of simplistic approaches, lack of spatio-temporal replication, use of artificial nests , and the effect of confounding variables. I attempted to clarify the equivocal findings of previous studies by using multiple regression to simultaneously examine the effect of several variables purportedly related to nest predation risk. I collected data on >1,800 dabbling duck nests and associated variables for 16 habitat patches (14 managed for duck production) during two nesting seasons in North Dakota. At the habitat patch level, early and late in each breeding season, I studied the relationship of nest success and upland area, nest density, predator abundance and richness, abundance of alternative prey for predators, and visual and physical obstruction provided by the vegetation . At the spatial scale of the nest and its neighborhood, I examined the likelihood of nest predation in association to nest initiation date, year, distance from nest to a wetland and to an edge, vegetation type at the nest, visual obstruction and heterogeneity of the vegetation around the nest, duck nest species , predator abundance, and presence/absence of 5 carnivorous predators at the nest habitat patch. Nest success was generally low and highly variable in time, and among and within habitat patches. I found no relationship between nest success and any of the variables measured at the patch scale. At the nest level, only initiation date, distance to water, visual obstruction, predator abundance, and duck species had an effect. High variability in the data and the lack of patterns in the relationship of nest predation and the predictor variables precluded me from building a predictive model that explains nest success. Nest success could not be predicted, predation was incidental and risk was high, and there were no safe nest sites for hens to choose in a landscape swamped by nest predators . Nests were located randomly; therefore, there were no clues predators could use to enhance their success in finding nests.

No description available.

Grain sorghum provides energy-rich seeds for waterfowl. I conducted experiments in 22 sorghum fields in Arkansas, Mississippi, and Louisiana during falls 2006 – 2007 to evaluate abundance of ratoon grain (i.e., second crop after harvest), waste grain, and natural seeds. I also conducted surveys of wintering waterfowl in flooded croplands and moist-soil wetlands to evaluate if ducks and geese differentially used habitats. Fertilized plots in 2007 produced >4 times more ratoon grain (x = 219.57 ± 39.65 [SE] kg/ha) than other treatments. Fertilized plots in southern regions of my study area produced ~5 times more ratoon grain (x = 262.93 ± 50.28 kg/ha) than others. Mallards and other ducks used moist-soil wetlands (x >65 ducks/ha) more than other habitats. I did not observe geese using flooded sorghum. I recommend not manipulating sorghum stubble after harvest, fertilizing, and flooding it after ratoon grain has matured, and integrating moist-soil wetlands into agricultural lands.

No description available.

No description available.

During the winter 1988-89, diurnal and nocturnal habitat use by juvenile female canvasbacks wintering on the upper Chesapeake Bay was determined. Radio-implanted canvasbacks used shallow water (0-2 m) areas near artificial feeding sites during the day, and deeper water (2-6 m) that had an abundant (> 200/m²) population of small (< 25 mm) Macoma balthica at night. Because of poorer Macoma populations on the east side of the Bay, canvasbacks there may feed more during the day and are in lower Macoma densities at night than west shore canvasbacks. Management of Chesapeake Bay canvasback populations should focus on providing natural foods and rest areas. / Master of Science

Call number: LD2668 .T4 1986 F87 / Master of Science / Biology

Disputats. Universität Hohenheim, 2003. / Haves kun i elektronisk udg.