The immunocompetence and immunomodulation of northern bobwhite quail (Colinus virginianus)
Arnold, Drew Garraway
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Bobwhite populations have been declining across their historic range for several decades. A number of hypotheses have been posited regarding factors contributing the observed decline. One such factor that that has recently gained attention from wildlife professionals is the contribution of disease and parasitism to bobwhite population regulation. Despite limited evidence implicating infectious agents in bobwhite population declines, researchers appear to largely disregard the role of the immune system in controlling said infectious agents. The immune system is the most important component of any organism’s defense against infectious agents. Although the immune system is well studied in a number of gallinaceous species (e.g. chickens and other poultry) there is a paucity of information regarding the immune system of bobwhites. Furthermore, the lack of information also pertains to the effects of varying factors encountered in the natural environment that may impact the immune system, susceptibility to infectious agents, and potentially mortality. Nutrition plays an important role in supporting the immune system with evidence of tradeoffs between other physiologically important processes and the immune system resulting from nutritional or resource limitation commonly encountered in natural systems. Other factors inherent to natural systems cannot typically be controlled by land managers (i.e. weather, disease processes, predation, etc.) with the exception of habitat management. Even then, responses of vegetative communities must yield to abiotic factors such as the weather (e.g. drought). However, nutritional pathways may be altered through the provision of supplemental food resources by land managers. Hence, nutritional pathways may be utilized to alter the immune function of bobwhites and consequently may buffer bobwhite populations against the effects of infectious agents if these processes are limiting bobwhite survival. The goals of my study were to assess whether measures of immune function from wild captured bobwhites were important parameters in bobwhite survival. To assess the effects of immune function on the survival of bobwhites, I utilized two immune assays; a bacteria killing assay (BKA) and an enzyme linked immunosorbent assay (ELISA) to assess the innate and adaptive immune function. I used the Nest Survival data type in Program Mark to asses survival of bobwhites captured over the years of 2010 – 2011, 2011 – 2012, and 2013 – 2014. Immune function measures (BKA and ELISA – denoted as IgY in survival models) as well as covariates related to year of monitoring, age (juvenile/adult), initial capture mass and feed supplementation status (supplemented/control) were utilized as covariates within the analysis to determine their relative importance in explaining survival. Only bobwhites with relevant immune data (BKA/IgY) were included to achieve a sample size of 124 individuals. The top models for survival through the analysis interval included the models containing the parameters, Year, Feed_Stat, and IgY. The top model (Year+Feed_Stat+IgY) contained the additive effects of all three aforementioned parameters (Wi = 0.501). The parameter Year was determined to be the most important parameter and appeared to “wash-out” the effects of Feed_Stat and IgY. A post-hoc analysis excluding Year indicated that Feed_Stat and IgY were the most important parameters. The model averaged probability of a bobwhite collected over a 3-year period surviving during the study was ~22% The role of nutrition on the bobwhite immune system was evaluated by providing a captive population of all male bobwhites with feeds of varying nutrient concentrations and compositions (i.e. vitamin, trace mineral, and antioxidant content.). The adaptive and innate immune systems were assessed via a battery of laboratory assays as well as in vivo assays. Diet did not influence innate immune function as measured by bactericidal killing capacity of serum, adaptive immune function measured as circulating immunoglobulin Y (IgY), and cell-mediated immune function as measured via subcutaneous swelling following phytohemagglutinin injection into the patagium. A significant time effect was observed for the adaptive and innate immune function parameters, circulating IgY and bactericidal killing capacity between time points (Day #1, Day #14, and Day #28). Through what nutritional pathways (e.g. nutritional component) the immune parameters were elevated is unknown. Whether nutritional quality is of consequence to the immune system of wild birds is yet to be seen and studies implicating nutritional profiles, available resources, and condition of bobwhites during immune compromising events warrants further study. The role of nutritionally supplemented diets consisting of varying nutritional qualities and components on muscle damage following extreme exertion was evaluated by providing a captive population of all male bobwhites with feeds of varying nutrient concentrations and compositions (i.e. vitamin, trace mineral, and antioxidant content.). Bobwhites were then exposed to a trial of muscular exertion for 15 minutes. Muscle damage resultant from exertion was assessed via determination of the concentration of enzymes indicative of muscle damage, creatine kinase (CK) and aspartate aminotransferase (AST) at 4 hours and 24 hours post exertion. Pathological examination of muscle tissues from the breast and thigh muscles were also utilized to determine effect of diet on incidence of muscle damage. A difference in CK concentrations between the NRC diet and NATURAL diet at 4 hours was observed. Four hours post exertion, CK concentrations in the NRC diet were an average of 8,690 +/- 3,572 U/L. No other differences between diets on CK and AST activity were observed at either 4 hours or 24 hours post exertion. I found that there was a significant difference in incidence of muscle damage as indicated by muscle damage lesion identification. It appears that nutritional quality did indeed affect muscle damage in bobwhites following strenuous muscular exertion, with bobwhites on the HVTM+A diet having the highest incidence of muscle damage as indicated by muscle damage lesions. The specific pathways regulating the occurrence of muscle damage in bobwhites fed diets with elevated nutrients is not known. However, the potential for reduction of muscle damage through increased nutritional supplementation does not appear in this specific study to be beneficial. A better understanding of the implications of specific nutrients, vitamins, antioxidants, etc. is necessary and additional research warranted.