UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
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Item Genetic consequences of habitat fragmentation and restoration(2012) Lloyd, Michael Warren; Neel, Maile C.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective my dissertation was to assess the effects of habitat loss and fragmentation on genetic diversity and landscape connectivity. I focused on Vallisneria americana Michx. (Hydrocharitaceae), a submersed aquatic plant species found in the Chesapeake Bay. Vallisneria americana has undergone dramatic changes in abundance and distribution throughout its range and has been targeted for restoration, which makes it ideal for examining the effects habitat loss and fragmentation. I examined the naturally occurring genetic diversity across the Chesapeake Bay and its major tributaries. Sites were genetically diverse, but had a range of genotypic diversities. There were four genetic regions, corresponding with geographic regions in the Bay. Vallisneria americana has been the target of restoration, and restoration techniques could be influencing genetic diversity and potentially lowering overall success. I examined various restoration techniques across eight restoration sites, and found that technique did not greatly influence genetic diversity. However, small population size, significant inbreeding coefficients, and low overlap of allele composition among sites provide cause for concern. Measures of functional and potential connectivity provide insights into the degree of contemporary gene flow occurring across a landscape. Pollen dispersal distance was measured using indirect paternity analysis, and is spatially restricted to only a few meters. Dispersal at this scale imposes small genetic neighborhoods within sites, evidenced by high seed relatedness within mothers. I used a graph theoretic approach to examine the distribution and potential connectivity of historic and current patches of V. americana. There was a high turnover in the distribution of patches, and connectivity varied through time, but even if all habitat were occupied, increases in overall network connectivity would not necessarily be observed. I developed an individual based model that I used to test the ability of measures of genetic differentiation to detect changes in landscape connectivity. Genetic differentiation measures became significant after two generations, but the magnitude of change in each was small in all cases and extremely small when population sizes are greater than 100 individuals. These results suggest that genetic differentiation measures alone are inadequate to rapidly detect changes in connectivity.Item CONSERVATION GENETICS OF THE ENDANGERED HAWAIIAN PETREL (PTERODROMA SANDWICHENSIS) ACROSS SPACE AND TIME(2011) Welch, Andreanna J.; Hawthorne, David J; Fleischer, Robert C; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The endemic Hawaiian Petrel (Pterodroma sandwichensis) is a long-lived pelagic seabird. Although endangered, subfossil evidence indicates that it was formerly more abundant in the past. In addition to a wider distribution on islands where the petrel currently breeds, two colonies, one on Oahu and one on Molokai, have been extirpated since humans colonized the Islands. Despite this, little is known about this species. Here I use conservation genetic and ancient DNA techniques to investigate the taxonomic status and population dynamics of the Hawaiian petrel. Investigation of the timing and magnitude of divergence between the Hawaiian petrel and its sister species, the Galapagos petrel (P. phaeopygia), revealed that these taxa diverged approximately 550,000 years ago. In a phylogenetic tree constructed from mitochondrial data Galapagos and Hawaiian petrels were reciprocally monophyletic, however, trees from the nuclear data set were unresolved. Low estimates of gene flow between taxa indicate that incomplete lineage sorting is causing the difference in resolution between data sets and that Galapagos and Hawaiian petrels are likely separate species. In addition to the mitochondrial and nuclear intron data sets, I developed a suite of 20 polymorphic microsatellite loci: I developed 10 specifically for the Hawaiian petrel, and characterized an 10 additional previously reported loci in this species. Using these three data sets I investigated the pattern of gene flow and divergence between modern, historical, and ancient populations of the Hawaiian petrel. The mitochondrial data set showed strong levels of differentiation between modern populations. The two nuclear data sets also revealed significant population structure, although it was weaker. Mitochondrial DNA sequences obtained from subfossil bones indicate that populations were significantly differentiated in the past, although there was low divergence between the extirpated Oahu and Molokai populations and modern birds from Lanai, suggesting that perhaps as colonies dwindled individuals dispersed to that island. Investigation of the effective population size indicates that no significant change has occurred on Hawaii or Maui. It appears that the long generation time of this species may have allowed it to escape a genetic bottleneck after the arrival of humans in the Hawaiian Islands.