Browsing by Author "Thomas Wentworth, Committee Member"

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Biodiversity and Biogeography of Limno-Terrestrial Tardigrades of North Carolina.
(2010-10-07) Ray, Margaret; Harold Heatwole, Committee Chair; Thomas Wentworth, Committee Member; Harry Daniels, Committee Member; Ted Emigh, Committee Member; Marianne Niedzlek-Feaver, Committee Member
Effects of disturbance on habitat dynamics of a rare species.
(2008-08-04) Bartel, Rebecca Anne; Justin Wright, Committee Member; Thomas Wentworth, Committee Member; James Gilliam, Committee Co-Chair; Nicholas Haddad, Committee Co-Chair
Interactions Between a Specialist and Generalist Moth and Their Host Plants
(2009-12-03) Petzold, Jennifer Lee; Wendy Boss, Committee Co-Chair; Ed Vargo, Committee Member; Thomas Wentworth, Committee Member; Fred Gould, Committee Co-Chair
Among the most significant issues regarding plant-herbivore interactions today are 1) elucidating the genetic architecture of host plant use and determining what factors are involved in locating and ovipositing on host plants, 2) understanding chemical interactions between insects and their host plants, and 3) understanding how plants evolve in response to the ecological pressures imposed on them by their insect pests, and how these insects in turn respond to these evolved mechanisms of host plant defense. The purpose of this research was to address these questions using a model system composed of two Heliothine moths, Heliothis subflexa and H. virescens. Heliothis subflexa (Hs) is a specialist that feeds only on plants in the genus Physalis, while H. virescens (Hv) is a broad generalist. To determine what genetic factors are involved in changes in host range, these two species were hybridized, and backcrosses to both parent species were produced. Larval feeding preference of Hs, Hv, and backcross lines was assessed using choice and no choice feeding tests on Physalis and tobacco (a host of Hv), and oviposition behavior was assessed by observing moths in a large outdoor cage containing Physalis and tobacco. We found that backcrosses in the Hs direction always resembled Hs in feeding and oviposition preference. Backcrosses in the Hv direction resembled Hv in oviposition behavior, but had intermediate feeding behavior and fed on both Physalis and tobacco. Hybrids showed strong preference for tobacco in oviposition behavior. These results show that at least one major locus is likely involved in feeding preference between the two host plants and that preference for Physalis is a dominant trait; however, genetic control of oviposition behavior on the two host species is more complicated to understand, possibly involving multiple genetic loci and a threshold effect, or few genes and a heterozygous disadvantage. Field experiments were also conducted to determine how Hs locates its host plants. Results showed that vision is an important host location cue, and confirmed prior studies that showed that Hs lays approximately 20% of its eggs on nearby non-hosts. A possible reason for this could be to avoid host plant defensesÃ¢â‚¬â€ Physalis plants were observed to respond to eggs of Hs; they do so by forming undifferentiated cells or a hypersensitive response directly under some Hs eggs. Laboratory and field studies demonstrated that eggs that elicited a response had a 25% lower probability of hatching, and a 28% lower probability of remaining on the plant. This resulted in a fitness cost of 18% for Hs, and it was concluded that response to eggs could be a factor that selected for non-host oviposition by Hs. Plants in this genus have also evolved to abscise fruits in response to fruigivory by Hs, but the degree to which chemical interactions are involved in this defense response was unknown. By using a combination of mechanical damage, natural damage, and Hs saliva and regurgitant treatments applied to fruit, it was determined that mechanical damage was sufficient to cause fruit abscission and insect oral secretions were not important in this response.
Long-term Impacts of Changing Land-use Practices on Water Quality and Phytoplankton Assemblages in the Neuse Estuary Ecosystem, North Carolina
(2007-11-13) Rothenberger, Megan Beth; Thomas Wentworth, Committee Member; Cavell Brownie, Committee Member; JoAnn Burkholder, Committee Chair; Dave DeMaster, Committee Member
The goal of this research was to build upon present understanding of the eutrophication process in the Neuse Estuary ecosystem by evaluating linkages among land use practices, nutrient concentrations and ratios, and phytoplankton assemblage composition. First, geographic Information Systems (GIS) analysis was used to characterize 26 sub-basins throughout the Neuse watershed for changes in land use over the past decade. GIS was also used in concert with multivariate statistics to synthesize and integrate ten years of land cover and water quality data into a conceptual model. Second, a continuous, decadal record of the phytoplankton in the mesohaline Neuse Estuary, in conjunction with synoptic measurement of environmental variables, provided a unique opportunity to evaluate responses of the phytoplankton assemblages to changing environmental conditions. Ordination techniques were used to investigate potential environmental predictors of phytoplankton community patterns through the process of eutrophication. Analyses indicated that over the past 10 years, total phosphorus concentrations were significantly higher during summer months in sub-watersheds with high densities of wastewater treatment plants (WWTPs) and confined swine feed operations. Nitrate concentrations were significantly higher during winter in sub-watersheds with high WWTP densities, and both inorganic and organic forms of nitrogen were significantly higher in sub-watersheds with greater agricultural land use. Ammonium concentrations were significantly higher after high-precipitation periods, but were not significantly correlated with the land-use parameters included in this study. In the Neuse Estuary, among several important findings, abundance of the potentially toxic, bloom-forming dinoflagellate Prorocentrum minimum was positively related to low water temperatures (winter⁄spring) and organic nitrogen and suspended solids concentrations. In addition, abundance of other potentially toxic flagellated algae such as the raphidophyte, Heterosigma akashiwo, has increased over the past decade, and H. akashiwo was found to be an "indicator species" for high ammonium concentrations (> 50 μg⁄L). Overall, the data indicate that wastewater discharges in the upper Neuse basin and intensive swine agriculture in the lower basin have been the highest contributors of nitrogen and phosphorus to receiving surface waters. In the estuary, increased nutrients, especially ammonium, are promoting increased abundance of several potentially toxic, bloom-forming phytoplankton species.