Browsing by Subject "avian"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Comparison of avian species diversity and densities on non-mined and reclaimed surface-mined land in east-central Texas(Texas A&M University, 2006-10-30) Wenzel, Dawn NicoleSurface mining often changes the native landscape and vegetation of an area. Reclamation is used to counter this change, with the goal of restoring the land to its original pre-mined state. The process of reclamation creates early successional-stage lands, such as grasslands, shrublands, and wetlands, attracting new plant and animal species to the area. I compared avian species density (number of individuals/ha), diversity (H'), and richness (number of species/ha) on reclaimed and non-mined lands at TXU's Big Brown Mine in Fairfield, Texas. I also compared my results to those of a previous study conducted 25 years earlier. Avian counts were conducted using a fixedradius point-count method on 240 points placed in four different vegetation types and in four land-age groups (time since being reclaimed). Vegetation was measured both locally, and at a landscape level. Overall bird species density did not exhibit a clear relationship on non-mined versus reclaimed land. Overall bird species diversity was greater on non-mined lands, whereas overall species richness was greater on reclaimed lands. My results demonstrated a lower mean/point bird density and higher mean/point bird diversity than were found 25 years earlier. Different nesting guilds occurred on the reclaimed lands than occurred on the non-mined lands. Results suggested different species were attracted to the several successional stages of reclaimed lands over the nonmined lands, which consisted of climax vegetation. The different successional stages of reclaimed lands increased overall diversity and richness of the landscape as a whole. Five bird species of conservation concern were observed in the study, all of which occurred on reclaimed land. Four of the five species primarily occurred on reclaimed lands. Future land management should include conserving different successional-stage lands to increase overall biotic diversity and richness of mined land, preserving reclaimed habitat for species of concern, and educating future private landowners on the importance of maintaining vegetative and bird species diversity.Item Roles for extra-hypothalamic oscillators in the avian clock(2009-05-15) Karaganis, Stephen PaulAvian circadian clocks are composed of a distributed network of neural and peripheral oscillators. Three neural pacemakers, located in the pineal, the eyes, and the hypothalamus, control circadian rhythms of many biological processes through complex interactions with slave oscillators located throughout the body. This system, an astonishing reflection of the life history of this diverse class of vertebrates, allows birds to coordinate biochemical and physiological processes and harmonize them with a dynamic environment. Much work has been done to understand what roles these pacemakers have in avian biology, how they function, and how they interact to generate overt circadian rhythms. The experimental work presented in this dissertation uses the domestic chicken, Gallus domesticus, as a model to address these questions and carry forward current understanding about circadian biology in this species. To do so, we utilized a custom DNA microarray to investigate rhythmic transcription in cultured chick pineal cells. We then sought to identify genes which might be a component of the pineal clock by screening for rhythmic transcripts that are sensitive to a phase-shifting light stimulus. Finally, we surgically removed the eyes or pineal from chickens to examine the roles of these extra-SCN pacemakers in regulating central and peripheral rhythms in metabolism and clock gene expression. Using these methods, we show that the oscillating transcriptome is diminished in the chick pineal ex vivo, while the functional clustering of clock controlled genes is similar. This distribution reveals multiple conserved circadian regulated pathways, and supports an endogenous role for the pineal as an immune organ. Moreover, the robustness of rhythmic melatonin biosysnthesis is maintained in vitro, demonstrating that a functional circadian clock is preserved in the reduced subset of the rhythmic pineal transcriptome. In addition, our genomic screen has yielded a list of 28 genes that are candidates for functional screening. These should be evaluated to determine any potential role they may have as a component of the pineal circadian clock. Finally, we report that the eyes and pineal similarly function to reinforce rhythms in brain and peripheral tissue, but that metabolism and clock gene expression are differentially regulated in chick.Item The suprachiasmatic nucleus of the domestic chicken, Gallus domesticus(Texas A&M University, 2007-04-25) Cantwell, Elizabeth LayneThe avian circadian system is composed of multiple inputs, oscillators and outputs. Among its oscillators is a hypothalamic structure presumed to be homologous to the primary circadian pacemaker in mammals, the suprachiasmatic nucleus (SCN). The SCN in avian species is poorly defined: two structures in the hypothalamus, the medial SCN (mSCN) and visual SCN (vSCN), have been referred to in the literature as the SCN. The present studies were designed to answer one central question: where is the avian homolog to the mammalian SCN? Uptake of 2-[14C]-deoxyglucose (2DG), an indicator of glucose metabolism, fluctuates in the mSCN and vSCN in both a daily and circadian manner. These data indicate a possible role in the circadian system for both the vSCN and the mSCN. Additionally, several visual structures display daily fluctuations of 2DG uptake, two of which exhibit circadian variations, supporting previous studies indicting circadian regulation of the visual system. Efferents and afferents of the mSCN and vSCN were identified and compared to those of rodents. While the mSCN bears a stronger resemblance to the rodent SCN in its efferent connections than the vSCN, afferents of both are comparable. The total number of mSCN and vSCN neuronal connections far exceeds that of the rodent SCN. A subset of these connections is strikingly similar to those of the rodent SCN, while others are found to connect these two nuclei to the visual system. These data further support the involvement of both the mSCN and vSCN in the circadian and visual systems. Suprachiasmatic organization was addressed using classical techniques. Though loosely similar in location to the mammalian SCN, the mSCN is cyto- and chemoarchitecturally different, while the vSCN bears more similarity to the mammalian SCN in this regard. A unique astrocytic bridge exists between the mSCN and vSCN, suggesting a role for astrocytes in the circadian system. Finally, the vSCN efferent to the medial nucleus of Edinger-Westphal was verified using a technique that may advance future studies of avian of circadian organization. The current data and the available literature were considered in the development of a working model of the avian SCN.