Browsing by Author "Coby Schal, Committee Member"

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Colony genetic structure and effects of inbreeding on body size in three populations of Reticulitermes flavipes in the southeastern U.S.
(2009-02-16) Nino, Bernardo Daniel; David Tarpy, Committee Member; Coby Schal, Committee Member; Edward Vargo, Committee Chair
In this study, I expanded the knowledge base of the eastern subterranean termite R. flavipes by investigating colony and population genetic structure in previously unstudied areas in Florida and Mississippi. I used microsatellite markers to infer colony breeding structure and population genetic structure and genotyped 20 workers in each of 20-30 colonies per population at eight microsatellite loci. I conducted pedigree analysis on the worker genotypes to determine the proportions of colonies that were simple families, extended families or mixed families. I also estimated the coefficient of relatedness and F-statistics and compared these values to those based on computer simulations of different breeding systems to infer levels of inbreeding and numbers of reproductives within colonies. An unexpected finding was the presence of two distinct populations in one collection site in Mississippi (MS). These two populations, MS1 and MS2, differed in the predominant family type. MS1 consisted mainly of simple family colonies whereas MS2 was composed primarily of extended family colonies. The breeding structure in the extended family colonies in both populations was consistent with simulations for colonies with a low number of effective reproductives (2-6) which have been interbreeding for few generations. In Florida I found a high proportion of extended family colonies (~ 63%); the breeding structure in these colonies was consistent with the presence of a higher number of effective reproductives (> 6) which had been interbreeding for many generations. Mixed family colonies were collected in all three populations and composed about 10% of all colonies in each population. In addition, I investigated possible effects of inbreeding and colony family type on worker and soldier body size. Worker and soldier head widths were measured and correlated to colony inbreeding coefficient (FIC). This statistic is highly sensitive to the number of effective reproductives heading colonies. A negative correlation was discovered between worker and soldier body size and the effective number of reproductives heading colonies in two populations. I found a similar trend in the third population (MS1) but it was not significant, most likely due to small sample size. In population MS2 I found a significant effect of colony family type on body size; workers and soldiers in extended family colonies were smaller than individuals in simple family colonies. These finding may indicate a previously little appreciated consequence of inbreeding in termites.
Comparative Study of the Breeding Systems of Reticulitermes flavipes and Reticulitermes hageni in a North Carolina Coastal Plain Site using Microsatellite Markers and mtDNA Sequence Data.
(2006-04-28) Dalton, Hope Anne; Edward L. Vargo, Committee Chair; Coby Schal, Committee Member; Jenny Xiang, Committee Member
The termites (Isoptera) are an important group of eusocial insects whose breeding systems have been relatively poorly studied. In this study, we inferred the breeding systems of two sympatric species of Reticulitermes flavipes (Kollar) and R. hageni Banks by investigating colony and population genetic structure using microsatellite and mitochondrial DNA markers. Termites were collected in natural wood debris along two transects 1 km apart in a forested site in the Coastal Plain of southeastern North Carolina. Collection points within transects were at least 15 m apart (mean = 22.4 m) and each collection point was found to be a separate colony based on microsatellite genotypes. Of the total colonies collected, eight colonies were identified as R. flavipes, 28 were R. hageni and two colonies were identified as R. virginicus. A total of 720 workers from 36 collection points were genotyped at 5-8 microsatellite loci and the mtDNA haplotype was determined for two individuals from each collection point at the cytochrome oxidase II gene. Genetic analysis of family structure and comparisons of F-statistics (FIT, FIC and FCT) and the coefficient of relatedness (r) were compared with computer-simulated values revealing very similar breeding systems between the two species. Analysis using F-statistics compared with computer simulated breeding systems (Thorne et al. 1999 and Bulmer et al. 2001) suggested that nearly 90% of the colonies of both species were simple families headed by inbred monogamous pairs of reproductives while the remaining colonies were extended (inbred) families headed by low numbers of reproductives that were descendants of the founding pair, possibly their direct offspring. There was no evidence of genetic differences between transects based on microsatellite data for R. flavipes (FST = 0.044, 95% confidence interval (CI) = -0.011 to 0.104) and evidence for a genetic difference between R. hageni transects (FST = 0.070, 95% CI = 0.025 to 0.108). This suggests a lack of budding and that mating flight dispersal is not limited over the study distance. These results indicate that within the study area R. flavipes and R. hageni have very similar breeding systems characterized by monogamous pairs of reproductives headed by slightly inbred reproductives and that few of these live long enough to produce more than a few neotenics. Results using mtDNA sequence data show two clades for each of the two species, R. flavipes and R. hageni. When comparing clades using microsatellite data, no significant difference between the clades was found for R. hageni, but a significant difference was found between clades for R. flavipes.
Effects of Synthetic Chemicals and Bacteria on the Oviposition Behavior and Electroantennogram Responses of Aedes albopictus (Diptera: Culicidae)
(2002-07-16) Trexler, Jonathan David; D. Wes Watson, Committee Member; Coby Schal, Committee Member; Charles S. Apperson, Committee Chair; W. Scott Chilton, Committee Member
Five volatile synthetic chemicals (dimethyl disulfide, indole, 4-methylphenol, 3-methylindole, and trimethylamine) were tested as potential oviposition attractants of Aedes albopictus (Skuse) in laboratory and field experiments. In addition, the oviposition responses of Ae. albopictus to bacterially-enriched substrates were evaluated in behavioral and electrophysiological bioassays as sources of attractants and stimulants. None of the five synthetic chemicals elicited a significant positive oviposition response. In laboratory bioassays that measured attraction of gravid females to olfactory stimuli, compounds were evaluated over a range of concentrations that spanned 4-5 logs. Three concentrations of 4-methylphenol and one concentration of 3-methylindole were significantly repellent. All other concentrations of the five chemicals tested did not attract more females than a water control. The five synthetic compounds were loaded into controlled-release packets, which were used to bait water-filled ovitraps at five suburban residences. Aedes albopictus exhibited no oviposition preference for any of the baited traps versus adjacent traps containing only water. In addition, there was no difference in the mean number of eggs laid per trap-day by Ae. albopictus among ovitraps treated with each of the five compounds. Electoantennography indicated that Ae. albopictus did not exhibit a physiological response to any of the five chemicals at 0.025 mg/L. The oviposition responses of Ae. albopictus to bacterially-enriched substrates were evaluated in laboratory bioassays. Gravid mosquitoes responded to volatiles from larval rearing water (LRW) and soil-contaminated cotton towels (T). Bacterial species were isolated from these substrates and from an organic infusion made with oak leaves (OLI). Through fatty acid-methyl ester analyses, 6 bacterial isolates from LRW, two isolates from T, and three isolates from OLI were identified to species. The response of gravid mosquitoes to these isolates was also evaluated in behavioral bioassays. Water containing Psychrobacter immobilis (from LRW), Sphingobacterium multivorum (from T) and an undetermined Bacillus species (from OLI) elicited significantly higher oviposition than control water without bacteria. Only volatiles collected from LRW elicited significant electroantennogram responses in females.
Genetic analysis of odor-guided behavior in Drosophila melanogaster
(2002-12-18) Ganguly, Indrani; Michael Purugganan, Committee Member; Eric Davis, Committee Member; Trudy F. C. Mackay, Committee Co-Chair; Robert R. H. Anholt, Committee Co-Chair; Coby Schal, Committee Member
The ability to respond to and interact with the chemical environment is fundamental to the survival of many species. It governs predator-prey relationships, kin and mate selection, food localization, maternal behaviors and avoidance of environmental toxins. Olfactory behavior is determined by the concerted action of multiple genes that interact with one another and with the environment, be it external, genetic or sexual. Like a number of other quantitative traits, odor-guided behavior shows significant sex-specificity in its phenotypic expression. However, the molecular basis of sexual dimorphism remains poorly defined. This study provides the first example of an autosomal pleiotropic gene that undergoes sex-specific transcriptional regulation to provide the potential for sexually dimorphic olfactory behavior. The phenotypic and molecular characterization of a P-element tagged locus, smi97B, reveals that the multiple PDZ (PSD-95, Discs-large, Zo-1) and LRR (Leucine-Rich Repeat) domain protein, Scribble (Scrib) is responsible for olfactory behavior in adult and larval stages of Drosophila melanogaster. In the adult, scrib is alternatively spliced to generate sex-specific transcripts that are correlated with sexually dimorphic olfactory phenotypes. Head-derived scrib splice variants differ in the number and positions of protein-interaction (PDZ and LRR) domains they encode. Since, Scrib is a synaptic scaffolding protein, these differences may direct the organization of sexually dimorphic synaptic signaling assemblies that contribute to odor-guided behavior.
The Genetic Basis of Hostplant Use in a Specialist and a Generalist Moth.
(2010-10-06) Oppenheim, Sara; Fred Gould, Committee Chair; Trudy MacKay, Committee Member; Coby Schal, Committee Member; George Kennedy, Committee Member; Ralph Dewey, Committee Member
Genetics of Sex Pheromones: Mapping Desaturase Genes in Heliothis Species.
(2009-11-30) Ward, Michael Duane Jr.; Christina Grozinger, Committee Member; Coby Schal, Committee Member; Fred Gould, Committee Chair
Many moths use a pheromone based sexual communication system where the female emits a precise mixture of volatile chemicals and only males who are physiologically tuned to that specific blend, respond. In order for the female to maintain her fitness, she must only attract conspecific males. If there were a mutation that caused a change in her pheromone blend it might be costly to the femaleÃ¢â‚¬â„¢s fitness. In the species Trichoplusia ni. and Ostrinia nubilalis, normal males have been shown to discriminate between normal and mutant pheromone blends. Therefore a species pheromone blend is likely maintained by strong stabilizing selection. However, it seems contradictory given the action of stabilizing selection that thousands of unique pheromone blends have evolved in Lepidoptera. One useful approach to understanding how this diversity may have arisen is to examine the steps in the biosynthetic pathways of pheromone production and to look for ways that changes in the pheromone blend may have had limited fitness cost. Two closely related species of moth in the Noctuidae family, Heliothis virescens (Hv) and Heliothis subflexa (Hs), have been used for studying the genetics of pheromone blend because, while they remain reproductively isolated in the wild, they can be crossed to produce hybrids with altered pheromone blends. Both species produce a multicomponent pheromone blend that is comprised of a precise ratio of 7 compounds including: tetradecanal (14:Ald), (Z)-9-tetradecenal (Z9-14:Ald), hexadecanal (16:Ald), (Z)- 11-hexadecenal (Z11-16:Ald), (Z)-11-hexadecen-1-ol (Z11Ã¢â‚¬â€œ16:OH), (Z)-9-hexadecenal (Z9-16:Ald), and (Z)-7-hexadecenal (Z7-16:Ald). With Hs and Hv producing different amounts of the individual components. Additionally, Hs produces 3 acetates that are not produced by Hv; (Z)-11, (Z)-9 and (Z)-7-hexadecanyl acetate. Our specific interest has been in the genes and enzymes that cause differences between the pheromone blends of these two species and the fact that the ratio of 16:Ald to Z9-16:Ald in Hv is greater than it is in Hs. Two pathways have been suggested that could produce this result, one where a ÃŽâ€ 9 desaturase converts 16:CoA to Z9-16:Ald and another where a ÃŽâ€ 11 desaturase produces Z11-18:Ald by desaturation of 18:CoA, which is then chain shortened to Z9-16:Ald. Previous experiments, using stable isotope labeled precursors, have shown no incorporation of 16:CoA into Z9-16:Ald in Hv suggesting that it is instead produced from 18:CoA. Here we take a slightly different approach where we look specifically for enzymes related to changes in pheromone components. Previous experiments in our lab have revealed 11 quantitative trait loci (QTL) that coded for differences between Hs and Hv in the proportions of 10 pheromone components. In this experiment, we combined previously obtained QTL information with heterologous probes designed using Helicoverpa zea and Helicoverpa assulta ÃŽâ€ 9 and ÃŽâ€ 11 desaturase genes respectively. We first probe for the desaturase genes in each species and then determine if these genes are found on any of the chromosomes that contain QTLs for changes in the ratio of 16:Ald to Z9-16:Ald. Based on our results, we conclude that the ÃŽâ€ 11 desaturase appears to be the only desaturase involved in the difference in the level of Z9-16:Ald between H. virescens and H. subflexa.
Immunobiochemical and Molecular Characterizations of Vitellogenesis in White Perch, Morone americana
(2008-06-24) Reading, Benjamin Jacob; Craig V. Sullivan, Committee Chair; John R. Godwin, Committee Member; Russell J. Borski, Committee Member; Coby Schal, Committee Member
Influence of Mosquito Larvae on Bacterial Species Diversity and Abundance, and on the Oviposition Response of Gravid Aedes aegypti (Diptera: Culicidae)
(2007-08-08) Evans, Brian Patrick; Michael Hyman, Committee Member; R. Michael Roe, Committee Member; Charles S. Apperson, Committee Chair; Coby Schal, Committee Member
The primary objectives of our study were to determine whether larval Aedes aegypti alter the bacterial community landscape of laboratory microcosms containing white oak (Quercus alba) leaf infusion (OLI) and to evaluate the degree to which a larval-altered bacterial community influences the olfactory⁄oviposition response of gravid Ae. aegypti. We found that the feeding activity of Aedes aegypti larvae influenced the production dynamics of bacterial food sources. Abundance (cells⁄ml of infusion) of total bacteria (culturable and unculturable species) declined from 8 to 28 d after addition of larvae while abundances of culturable bacteria were largely unaffected by the presence of larvae over a 32-d period. On average, abundance of culturable bacteria accounted for only 2.5% of the abundance of total bacteria in oak leaf microcosms, which suggests that larvae primarily fed on unculturable bacteria. Bacterial community structure for microcosms with and without larvae was profiled with denaturing gradient gel electrophoresis (DGGE) using PCR-amplified 16S ribosomal DNA fragments from extracted total genomic DNA. Analysis of matrix distance coefficients between DGGE profiles using non-metric multi-dimensional scaling demonstrated a larval effect on the bacterial community structure beginning on days 12 or 16 to the end of the experiment (day 32). Additionally, we discovered that over consecutive days, particularly prominent DGGE bands (= bacterial operational taxonomic units) which had appeared in profiles of larval microcosms, were either absent or found at proportionately lower intensities in corresponding profiles from microcosms in which larvae had been absent and vice versa. Such findings provide evidence that mosquito larvae alter the bacterial community structure in laboratory microcosms. To determine whether alteration of the bacterial community structure in OLI by mosquito larvae influenced the olfactory/oviposition response of gravid mosquitoes, we used a binary bioassay to evaluate the attractant/repellent and stimulant⁄deterrent properties of OLI which contained larvae. Each experimental replicate produced a different olfactory⁄oviposition response pattern over the 32 d of the experiment, indicating that larval alteration of the bacterial community structure had no consistent effect on the olfactory/oviposition response of gravid adults. However, for some experimental replicates, the occurrence of some DGGE gel bands or band patterns was associated with an enhanced oviposition response. Laboratory experiments were also carried out to investigate the fitness of larval cohorts of Ae. albopictus (Skuse) and Ae. aegypti L. in microcosms containing white oak leaves as a source of detritus. Some microcosms contained whole leaves while leaf particulates were added to other microcosms to simulate the activity of leaf-shredding arthropods in a detritus processing chain. Larval performance variables (larval survival and development time, and adult emergence) in these microcosms were separately evaluated for both mosquito species in factorial experiments involving combinations of larval density (0.5 and 1.0 larvae per mL) and leaf biomass (4.2 and 16.8 g⁄L). Ae. albopictus exhibited superior larval fitness relative to Ae. aegypti at each level of larval density and leaf biomass and for each leaf condition evaluated. Ae. albopictus and Ae. aegypti responded differently to leaf condition, which suggests that processing chain interactions between these species and top-level consumers would vary in nature.
Mating disruption for control of the Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera:Tortricidae), in North Carolina apple orchards.
(2003-07-31) Kovanci, Orkun B; Coby Schal, Committee Member; George G. Kennedy, Committee Co-Chair; Turner B. Sutton, Committee Member; James F. Walgenbach, Committee Co-Chair
Oriental fruit moth, Grapholita molesta (Busck), has been a primary pest of peaches for many years throughout the world, and recently it has also emerged as a key pest of apples in the eastern United States. The implementation of the Food Quality Protection Act has eliminated the use of many organophosphate insecticides and encouraged the search for alternatives to organophosphates for control of Oriental fruit moth. Large and small plot studies were conducted to evaluate mating disruption as an alternative control tactic against Oriental fruit moth in North Carolina apple orchards during 2000-2002. The efficacy of Isomate-M 100 pheromone dispensers and microencapsulated sprayable pheromone was compared to insecticide-treated and non-managed orchards. Pheromone trap catches were significantly reduced in mating disruption blocks compared with conventional and non-managed orchards. Pheromone traps placed in the upper canopy captured significantly more moths than traps placed in the lower canopy across all treatments. Male OFM responded optimally to traps baited with 100 μg lures compared with 30 and 300 μg lures regardless of treatment. The loss of OFM pheromone from red rubber septa over a four-wk period exhibited a first-order release rate for septa loaded with 100 and 300 μg pheromone, but a more constant release rate from septa loaded with 30 μg pheromone. Based on pheromone trap captures, there was little difference among rates of sprayable pheromone ranging from 12.4 to 49.1 g (ai)/ha, but efficacy declined at 2.4 g (ai)/ha applied at monthly intervals. The 6.2 g (ai)/ha rate applied at 2-wk intervals was significantly less effective than monthly applications of 12.4 and 24.7 g (ai)/ha. Significantly fewer moths were caught in pheromone traps deployed in blocks treated in late May with Isomate-M 100, Isomate-M Rosso and Isomate-M 100 plus 3M sprayable pheromone compared with traps in conventional insecticide treatments, and Isomate-M 100 applied in late June. Overall, fruit damage by OFM larvae was quite low in mating disruption blocks.
Spatial Ecology of Aedes Albopictus in Suburban Landscapes of a Piedmont Community in North Carolina
(2005-09-25) Richards, Stephanie Lynn; Coby Schal, Committee Member; Bruce Harrison, Committee Member; Charles S. Apperson, Committee Chair; Jules Silverman, Committee Member; Heather Cheshire, Committee Member
The objectives of our study were to investigate the spatial ecology of Ae. albopictus, to evaluate some potential management methods, and to characterize its host feeding patterns in a suburban landscape. We monitored Ae. albopictus oviposition activity with oviposition traps at fixed stations, conducted container surveys for larvae and pupae, and collected adults from vegetation at residences in eight suburban neighborhoods in Raleigh, NC during the 2002 and 2003 mosquito seasons. Host sources of blood fed mosquitoes were determined by an indirect Enzyme Linked Immunosorbent Assay, using antisera made in New Zealand white rabbits to the blood serum proteins of humans and, domestic and wild animals. An area-wide management strategy involving a lethal oviposition trap (LOT) placed in the landscape around homes in suburban neighborhoods was evaluated. The trap consisted of a black plastic cup filled with water and containing an oviposition substrate impregnated with an insecticide. Source reduction (SR) of water-filled containers was also evaluated as a management strategy for Ae. albopictus in combination with the LOT and as a stand-alone area-wide approach to control. Analysis of variance did not reveal any significant mosquito suppression (P > 0.05) resulting from the LOT, SR, or the combination of LOT and SR during the 2002 and 2003 mosquito seasons. We determined that the mosquito production potential of a container was a function of its pupal standing crop, density, and spatial distribution in the landscape. Spatial statistical methods were used to evaluate impacts of SR of man-made, water-holding containers on the spatial structure of the population of Aedes albopictus immatures. Spatial analyses considering the presence or absence of pupae revealed that residences with at least one pupa-positive container tended to be dispersed throughout SR areas and clustered throughout control areas, indicating that SR affected the spatial distribution of pupae. We used kriging to show the spatial distribution of oviposition activity within neighborhoods. Areas of high and low egg production existed in most neighborhoods; however, spatial patterns of oviposition changed between seasons. Oviposition activity peaked in late summer in both the 2002 and 2003 mosquito seasons. Aedes albopictus primarily fed on mammals, but took blood meals from 12 different hosts or host classes, including birds, frogs, and turtles. The largest proportion of blood meals was taken from humans, followed by cats and dogs. Host feeding indices were calculated for human and domestic animal hosts based on the proportion of host specific blood-fed mosquitoes per collection in relation to the number of corresponding specific hosts per residence established from a door-to-door host survey. When host abundance was considered solely, host-feeding indices indicated that Ae. albopictus was more likely to feed on domestic animals. When feeding indices included host abundance that was time-weighted based on potential exposure to mosquitoes, Ae. albopictus fed preferentially upon humans.
The Synchrony of Herbivore Presence, Induced Plant Volatiles, and Parasitoid Response
(2007-07-18) Puente, Molly Elizabeth; Coby Schal, Committee Member; Fred Gould, Committee Co-Chair; George Kennedy, Committee Co-Chair; Nicole Darnall, Committee Member; Nick Haddad, Committee Member
Parasitoids find chemical volatiles produced by herbivore-damaged plants attractive. It has been suggested that by manipulating these volatiles in crop plants, biological control can be enhanced in agricultural systems. Before this technology is implemented, it is important to understand the dynamics of the system. I used two different modeling approaches to address this phenomenon. In the first model, I combined a modified predator-prey functional response equation with an age-structured herbivore population model. In the second model I took a spatially-explicit stochastic simulation approach and examined the Brassica oleraceae, Pieris rapae, and Cotesia rubecula system in more detail. I looked at the effects of plant induction delay, plant relaxation delay, herbivore density, and parasitoid host-age preference. In both models, parasitoids gained the most from signals when all herbivore instars were viable hosts, herbivore density was low, and relaxation delays were short. In the stochastic simulation model, shorter induction delays could lead to considerable gains for the parasitoids. Together, the models indicate that there are some conditions that favor parasitoids following herbivore-induced plant volatiles. By creating plants that produce signals in the right time frame, it may be possible to optimize biological control. However, it is also apparent from my models that herbivore-induced volatiles are ineffective during herbivore outbreaks because parasitoids are limited by factors other the time it takes to find hosts, which is the primary way herbivore-induced plant volatiles aid foraging parasitoids. Improving biological control is one of the practices growers can adopt as part of Integrated Pest Management (IPM), and in the final section of this dissertation I discussed a survey exploring how growers adopt IPM. I found that practices consistent with IPM were adopted in a piecemeal fashion by cotton growers in Eastern North Carolina. My analysis indicated that growers did not see all these practices as part of a single management decision, but rather as parts of independent decisions dealing with weed management, insect management, crop management, and ecosystem management.
Synthesis of Nicotine Derivatives from Natural Nicotine, Total Synthesis of (S)-Brevicolline, and Advances towards the Synthesis of Dihydrolycolucine.
(2006-08-10) Wagner, Florence Fevrier; Coby Schal, Committee Member; Christian C. Melander, Committee Member; Daniel L. Comins, Committee Chair; T. Brent Gunnoe, Committee Member; Suzanne Purrington, Committee Member
Nicotine and its derivatives are currently being synthesized and tested to explore their pharmaceutical capabilities in the treatment of Alzheimer's disease, Parkinson's disease, and other central nervous system disorders. One area of research the Comins group has been undertaking is the development of methodologies for the synthesis of nicotine derivatives from natural nicotine. Herein, regioselective substitutions of the pyridine ring of (S)-nicotine will be described. Efforts are underway to expand the scope of these methods and to apply them to the preparation of potential pharmaceuticals, insecticides, synthetic intermediates, and novel ligands for catalytic asymmetric synthesis. Nicotine was used as a building block for the syntheses of SIB-1508Y, a potential anti-Parkinson's drug, which was successfully synthesized enantiomerically pure in only five steps. (S)-Brevicolline, a natural product of the -carboline family was synthesized from nicotine in only six steps. Our goal is to transform inexpensive, commercially available (S)-nicotine from an underutilized natural product to a useful member of the chiral pool. Our group previously reported the intramolecular Diels-Alder reaction of 1-acyl-2-alkenyl-1,2-dihydropyridines. A derivative of a dihydropyridine Diels-Alder product could be ring-opened via a Retro-Mannich reaction to give a cis-decahydroquinoline derivative. The potential of this methodology for the synthesis of dihydrolycolucine, natural product from the Lycopodium family, prompted us to carry the model studies described in Chapter IV.