Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    MULTIDISCIPLINARY APPROACH TO UNDERSTANDING THE POOR REPRODUCTION IN THE WHOOPING CRANE (GRUS AMERICANA)
    (2013) Brown, Megan Elizabeth; Songsasen, Nucharin; Keefer, Carol L; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Reproductive success of the endangered whooping crane (Grus americana) maintained ex situ is suboptimal. The main goals of this multidisciplinary investigation are to advance the understanding of whooping crane reproduction and identify potential causes of poor reproductive success in a captive colony. The specific objectives include (Study 1) determining overall seminal characteristics and examine the influences of inbreeding, age, and stages of breeding season on seminal quality in captive birds and (Study 2) utilizing non-invasive endocrine monitoring to longitudinally assess gonadal and adrenal steroids of bird pairs with various reproductive outcomes and evaluating the relationship between hormones and crane behaviors. Our findings demonstrate that (1) there is no relationship between inbreeding coefficient or age and seminal quality of the whooping crane and (2) stage of breeding season impacted seminal output and characteristics. Overall estradiol concentrations and reproductive behaviors, but not glucocorticoid levels, were also key determinants to successful reproductive output.
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    Behavioral and Neuroendocrine Correlates of Sex Change in the Gilthead Seabream (Sparus aurata)
    (2009) Reyes-Tomassini, Jose J.; Zohar, Yonathan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Sequential hermaphroditism is the most radical form of environmental sex determination observed in fish: functional adult males or females retain their ability to change sex even as adults. Among the factors that affect sex change in these species, the least understood is the social environment. Here, I studied the influences of social context on sex change in the Gilthead Seabream, Sparus aurata, by using the individual‟s dominance rank as an indicator of social status. To understand the role that the brain might play in sex change, I also studied the two main neuroendocrine factors that serve as the sexually differentiated axes of neural plasticity in most teleost species: AVT and GnRH. To do this, I first developed a set of tools designed to address the challenges associated with observing the behavior of aquacultured species. Using these tools, I provide the first in-depth study of seabream captive behavior, including the results of size-matched and sex-matched paired encounters. I found that females are more aggressive than males, but this difference is influenced by gonadal developmental status. I also showed that small but young males are more aggressive than bigger but older females. I cloned the AVT mRNA in seabream, and validated a quantitative assay to measure total brain AVT levels together with GnRH-1, GnRH-2, and GnRH-3 levels. I found that AVT and GnRH-3 levels rise during the onset of the hypothesized sex-change window, and drop to pre-quiescent levels until spawning, when all of these factors seem to increase their expression levels again. I also show for the first time, that GnRH-2 and dominance rank are strongly correlated in seabream during the spawning season but not during quiescence. GnRH-1 was strongly correlated to rank during quiescence but not during spawning. Finally, neither dominance rank nor size were a good predictor of the outcome of sex change, which seems to contradict what has been documented in sequential hermaphrodite reef fishes. I provide a model that accounts for this apparent contradiction and conclude that the Gilthead seabream remains true to the size-advantage hypothesis of sex allocation theory, if size and dominance are seen as proximate, rather than ultimate, factors.