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Combining methods of analysis to understand the demography of corals : an example for populations of the mushroom coral Fungia fungites exposed to contrasting regimes of disturbanceGilmour, James Paton January 2005 (has links)
[Truncated abstract] Most ecological research investigates the demography of organisms, which can be summarised by their population dynamics and structure. Population dynamics are the rates of birth, growth, reproduction and survival of individuals, which determine the number of individuals in different stage classes, or, the population structure. Understanding the demography of organisms is particularly difficult, and requires the application of different methods of investigation. A number of methods of investigation are required because each can only investigate particular aspects of population demography, and is subject to problems of inaccuracy and bias. Thus, population demography is best understood by simultaneously collecting complimentary data using different methods of analysis to quantify how and why the dynamics and structure of populations change with their environment. The need for complimentary methods of investigation to understand population demography is even greater for organisms that have complex life histories, such as corals. The life histories of corals are particularly complex because they display a variety of modes of sexual and asexual reproduction, and their rates of growth, reproduction and survival are strongly influenced by the size of the individual, which can change rapidly. Additionally, the rates of sexual recruitment to populations of corals are notoriously variable in space and time. Thus, corals are an ideal model to investigate the usefulness of combining methods of analysis to better understand the demography of organisms. In this thesis I demonstrate that combining data from a number of methods of analysis provides a much better understanding of the demography of populations of the mushroom coral Fungia fungites that were exposed to contrasting regimes of disturbance. I used methods of analysis that produce unique and complimentary results, in the form of genetic, size-structure, life history and experimental data. Genetic data confirmed that I was correctly identifying life history stages of polyps, indicated the extent to which a stock-recruitment relationship existed between the sexual recruits and the adult polyps at each population, and provided an estimate of the relative contribution of asexual recruitment to population maintenance. Changes in the size-structures of populations were quantified to determine the effects of different regimes of disturbance, and these changes in population structure were explained by quantifying the life history traits of polyps and their rates of transition through their life cycle. An experimental manipulation was conducted to specifically quantify the effects of sedimentation on the rates of survival and asexual recruitment of polyps, because sedimentation was an important disturbance whose effects were confounded by additional variables. Together, the set of complimentary data provided a good understanding of population demography in the context of varying levels of exposure to certain disturbances, and enabled the best possible predictions about the future of each population under a variety of conditions
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Exploring the cellular mechanisms of Cnidarian bleaching in the sea anemone Aiptasia pallidaPerez, Santiago 03 April 2007 (has links)
Many members of the Phylum Cnidaria are mutualistic with unicellular
dinoflagellates belonging to the genus Symbiodinium. Corals are the most widely
recognized example of these associations due to their key ecological importance in
coral reef ecosystems where they serve as the structural and trophic foundation of
these rich ecosystems. Coral reefs are severely threatened by human activities worldwide
and are at great risk from global climate change, in particular the increase in seasurface
temperatures. Detailed knowledge of how corals respond to stress is scarce.
The most serious and immediate response of corals to environmental stress is a
process referred to as coral bleaching (a.k.a. cnidarian bleaching). Nevertheless, the
cellular and molecular processes by which elevated temperatures elicit the bleaching
response are poorly understood. This dissertation deals with this important question
by describing two mediators of cnidarian bleaching in the model symbiotic tropical
sea anemone Aiptasia pallida (Verril), namely nitric oxide and cyclophilin.
After an introduction to the topic of cnidarian-algal symbioses and cnidarian
bleaching (Chapter 1), I present results from a study describing the involvement of
nitric oxide (NO) in the anemone A. pallida (Chapter 2). Elevated temperature as well
as oxidative stress induces production of NO and exposure of A. pallida to NO induces
bleaching at non-stressful temperatures. Co-incubation with an NO scavenger
suppresses bleaching. I propose that the host up-regulates NO production in response
to elevated oxidative stress and that this situation leads to cytotoxicity and bleaching.
Chapter 3 examines the role of cyclophilin from A. pallida in the regulation of
the symbiosis. Cyclophilins belong to a highly conserved family peptydyl-prolyl cistrans
isomerases (PPIases). Incubation of A. pallida with cyclosporin A (CsA), a
potent inhibitor of cyclophilin resulted in bleaching and a decrease in tolerance to
elevated temperatures. Protein extracts from A. pallida exhibited CsA-sensitive
PPIase activity. Laser scanning confocal microscopy using superoxide and nitric
oxide-sensitive fluorescent dyes on live A. pallida revealed that CsA strongly induced
the production reactive oxygen species as well as NO. We tested weather the CsAsensitive
isomerase activity is important for maintaining the activity of the antioxidant
enzyme superoxide dismutase (SOD). SOD activity of protein extracts was
not affected by pre-incubation with CsA in vitro. In Chapter 4 I review what is known
about the molecular and cellular mechanisms of bleaching and describe a model of
bleaching based on the results presented herein as well as studies of non-cnidarian
models. / Graduation date: 2007
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