Animal & Avian Sciences Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2741
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Item Post-bottleneck inbreeding accumulation reduces fitness in laboratory populations of Tribolium castaneum under environmental stress(2008) Choiniere, Ashley Danielle; Siewerdt, Frank; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Populations are often driven to extinction due to low genetic diversity. One major cause for loss of genetic diversity in a population is a demographic bottleneck. A demographic bottleneck was imposed on twenty-one populations of Tribolium castaneum using multiple strategies. After recovering to original census numbers, the populations were subjected to stressful environments, and fitness was quantified. There was a significant decrease in additive genetic variance in all populations as a result of the bottleneck event (P<0.05). As estimated inbreeding accumulation increased, there was a decrease in the mean of fitness related traits, such as adult weight, total progeny, fecundity and survivorship. This relationship was best explained using quadratic models and became even more significant when the populations were under stress. This suggests that both dominance and epistatic gene effects are playing a role in phenotypic expression of traits and that expression may be flexible, supporting survival and fitness.Item EPIDEMIOLOGIC ANALYSIS OF RISK FACTORS FOR LOCAL DISAPPEARANCES OF NATIVE RANID FROGS IN ARIZONA(2005-08-11) Witte, Carmel Lee; Kane, Andrew S.; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study used epidemiologic case-control methodology to examine habitat and environmental factors contributing to amphibian declines in Arizona. Risk factors were compared between sites where frogs disappeared (cases) and persisted (controls) using univariate and multivariable logistic regression analyses. Thirty-six percent (117/324) of all sites became cases during the study period. Elevation, non-native predators, hydrologic characteristics, aspect, and effects of nearby sites were significantly associated with frog persistence or disappearance. In the final multivariable model, risk for disappearance increased with increasing elevation (OR=2.7 for every 500 meters, P<0.01). Sites where disappearances occurred were 4.3 times more likely to have other nearby sites that also experienced disappearances (P<0.01), while having an extant population nearby decreased risk of disappearance by 85% (OR=0.15, P<0.01). Sites experiencing disappearances were 2.6 times more likely to have crayfish than control sites (P=0.04). Identification of risk factors associated with frog disappearances will guide future research and conservation efforts.Item Effects of embryonic exposure to androgen-active endocrine disrupting chemicals in Japanese quail(2005-04-18) Quinn, Jr., Michael James; Ottinger, Mary Ann; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Endocrine disrupting chemicals (EDCs) are compounds that alter the production, secretion, action, and elimination of endogenous hormones. EDCs have been shown to be responsible for disrupting development, reproduction, immune function, behavior, and all other life functions mediated by hormones. In the environment, organisms are exposed to many different types of EDCs at any one time, each with different mechanisms of action, many of which are not fully understood at present. Most research done with EDCs has focused on the effects of these chemicals on the estrogen and thyroid systems, however, many of these same chemicals also exert strong effects on the androgen system. Also, many studies assessing the effects of EDCs on wildlife have focused on reproductive measures of exposure, often overlooking potential effects on the immune system. We have demonstrated that embryonic exposure to androgen-active EDCs, anti-androgenic DDE and androgenic trenbolone acetate, impairs development of the bursa of Fabricius in Japanese quail, providing a possible mechanism for EDC-induced immunosuppression. The bursa is a primary immune organ responsible for development of the humoral part of the immune system. We have also demonstrated that the bursa can be resilient to embryonic exposure to EDCs, if post-hatch exposure to these chemicals is prevented. Measures of reproduction, behavior, growth, and developmental stability were also taken in this study. Male and female rates to sexual maturity were altered by the one-time in ovo exposure to DDE and trenbolone. Male reproductive behavior, as measured by attempts to mount and successful cloacal contacts achieved, was suppressed by both chemicals. Vocalization was abolished in one and two week old chicks from the highest trenbolone acetate treatment levels. Although environmentally relevant, the levels of DDE used in this study were below those reported to affects avian reproduction. Environmental levels of trenbolone acetate are unknown, however, previous studies have concluded trenbolone acetate to be safe to wildlife and non-teratogenic. The myriad of endpoints used in this study has been compiled to provide toxicologists with a list of sensitive and persistent measures that can be used as reliable biomarkers of exposure to androgen-active EDCs in birds.