Browsing by Subject "Larvae"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Effects of post-settlement habitat use and biotic interactions on survival of the seagrass-associated fish red drum (Sciaenops ocellatus)(2009-12) Fencil, Megan Christine; Holt, J. (Joan); Dunton, Kenneth H.; Montagna, Paul A.; Rocha, Luiz A.; Rooker, Jay R.Due to high mortality encountered by marine fish larvae during their first weeks of life, small changes in the number of individuals surviving through this period can cause large fluctuations in year-class strength. Larval Red Drum (Sciaenops ocellatus) are dependent upon structured estuarine habitat to avoid predation. A study of post-settlement larval Red Drum distribution in a subtropical seagrass meadow in Mission-Aransas Estuary, Texas, USA indicates that larvae settle over approximately two months. Abundance of larger settled larvae was significantly different among sites. The areas of highest larval abundance varied temporally, indicating that the entire extent of the seagrass bed is utilized. Regression analysis of abiotic environmental factors did not explain why larvae were more abundant at particular sites. To characterize the structure and variability of the fish species assemblage that Red Drum encounter upon settlement, larvae and juveniles were captured in the seagrass meadow during weekly collections. Of the 32 fish species collected, seven represented 92% of the assemblage. Multivariate species analysis indicated that collections widely separated in time and space shared the lowest Bray-Curtis similarity. Because Red Drum settle over a relatively long period and co-occur at body sizes known to cause cannibalism under laboratory conditions, I tested combinations of small and large Red Drum larvae at various field-realistic densities and at different levels of seagrass habitat structure to determine potential for cannibalism. Artificial seagrass did not protect small (5 – 6 mm SL) larvae from cannibalism, but natural dense seagrass had a protective effect relative to edge habitat. The final component of this research examined the emergent impacts of a common predator pinfish (Lagodon rhomboides) on mortality and cannibalistic interactions between small and large Red Drum larvae. Both pinfish and large Red Drum larvae alone readily consumed small Red Drum in all seagrass habitat structures tested. However, the combined treatment of pinfish and large Red Drum together led to reduced mortality of small Red Drum. Predation can significantly affect Red Drum survival during the post-settlement period, and multiple predators may have a protective effect on the smallest settlers if predation pressure is re-directed towards a larger size class.Item Ethanol dependence in Drosophila larvae(2013-08) Robinson, Brooks Gregory; Atkinson, Nigel (Nigel S.)Addiction to alcohol is a disease of changed behavior that is uniquely human in it's complexity. Because of this, researchers have strived to develop animal models of individual endophenotypes of alcoholism in hopes that the larger picture will eventually come into focus. Recent studies in Drosophila have shown that many complex alcohol-related behaviors are conserved in this genetic model system. The series of projects presented in this dissertation outline the first account of physiological ethanol dependence in Drosophila. We first show that Drosophila larvae are able to form conditioned associations between an aversive heat stimulus and an attractive odor. We then show that an acute, low-dose ethanol exposure disrupts this learning ability. Finally, we present data that demonstrate that larvae adapt to the presence of chronic ethanol to the point that they only perform normally in the learning assay when ethanol is present in the animal. We then propose that the major mechanism for this dependence involves ethanol regulating the acetylation level and therefore expression level of a large number of genes by inhibiting histone deacetylase enzymes. These experiments set the groundwork for the analysis of a network of genes, connected through interactions with histone deacetylase enzymes, that are involved in producing ethanol dependence.Item Mathematical modeling of Drosophila larvae crawling(2013-12) Guenther, Maximilian Norbert; Shubeita, George T.; Florin, Ernst-LudwigThe fruit fly Drosophila melanogaster is a widely used model organism for development and gene-based diseases. The flies’ genetic homology to humans, tractable genetics and straightforward manipulability make them well suitable for studies of neurologic disorders and neural degeneration. Due to the close relation between the latter and the musculoskeletal system, locomotive impairment and behavioral changes can be used diagnostically for screening and characterization of such disease models. For this purpose, advanced methods to quantify behavioral phenotypes are crucial. Given the complications arising with studying adult flies on a population level as well as the lethality of some mutations before adulthood, studies at the larval stage are more suitable. However, a quantitative mathematical model of the crawling pattern has been lacking so far. In this thesis work I show that the development of such a model and appropriate analysis techniques enable quantification of the crawling behavior and extraction of intricate details that were previously missed. In my studies, Drosophila larvae were found to follow a bimodal persistent random walk pattern, switching between an actual forward crawling phase and events where the larvae rest and reorient. This enabled quantifying the larval behavior using a set of parameters within the framework of this mathematical model. I further used the analysis I developed to study larval model systems of Alzheimer’s disease and Fragile X mental retardation, which allowed identifying differences in the modes of locomotion that were previously missed. The novel ability to sensitively and robustly quantify behavior, as described in this work, opens up the possibility to employ these methods for future drug and genetic screens. Finally, I show that starting from the analysis of a small sample of crawling larvae we can robustly simulate the mutant-specific crawling in its quantitative and qualitative aspects. Using these simulations, predictions can be made on the feasibility of experiments that may require an impractically large number of individuals to reach statistical significance, and the outcome of laborious experiments can be pre-estimated by simulations.