Browsing by Author "Christina M. Grozinger, Committee Co-Chair"

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    Analysis of molecular and physiological pathways regulating social behavior in honey bees: elucidating the role of Kr-h1 and cGMP
    (2009-12-04) Fussnecker, Brendon Louis; James W. Mahaffey, Committee Chair; Christina M. Grozinger, Committee Co-Chair; Patricia A. Estes, Committee Member; Eric A. Stone, Committee Member
    Kruppel homolog 1 (Kr-h1) is a zinc finger transcription factor whose brain expression levels are associated with foraging behavior and are regulated by queen mandibular pheromone (QMP) in honey bees. We used behavioral, physiological, and genomic approaches to investigate the factors which regulate expression of Kr-h1 in honey bees, and employed a comparative genomics approach to begin to characterize the molecular function of this protein. We demonstrated that brain expression of Kr-h1 is associated with permanent physiological changes that occur during behavioral maturation from nursing to foraging, rather than the acute expression of foraging behavior. Furthermore, we demonstrated that Kr-h1 expression is modulated by cGMP, a key regulator of behavior maturation, and identified a potential cGMP response element in the promoter of Kr-h1. We then characterized the interactions between cGMP and QMP. cGMP inhibited behavioral and physiological responses to QMP, and partially inhibited expression changes of QMP-responsive genes in the brain. Treatment with these factors specifically altered expression of genes associated with GTPase regulator activity, phototransduction, and positive regulation of antibacterial peptide biosynthetic process. However, cGMP did not affect the expression of AmOr11, an odorant receptor specific for a major chemical component of QMP, suggesting that cGMP might work centrally rather than peripherally to modulate the response to QMP. Finally, we elucidated changes in gene expression that resulted from the absence of Kr-h1 expression during D. melanogaster development and discovered an associated motif in the promoter of the majority of the significantly expressed genes, which may mediate the effects of Kr-h1. Further analysis, however, showed that this motif is unlikely to be biologically relevant. These studies have demonstrated the ability of physiological factors to modulate responsiveness to social cues, and provided further information about the role of Kr-h1 in regulating behavior in bees.
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    Molecular and Physiological Mechanisms Underlying Chemical Communication in the Honey Bee, Apis mellifera.
    (2009-12-03) Ayroles, Sarah DeLeigh; Trudy F.C. Mackay, Committee Chair; Christina M. Grozinger, Committee Co-Chair; W. Owen McMillan, Committee Member; David R. Tarpy, Committee Member
    From prokaryotes to vertebrates, the use of chemical signals is widespread. However, the underlying mechanisms that have led to the diversification of chemical communication are poorly understood. Here, I focus on the pheromonal communication system of the honey bee, Apis mellifera, and describe some of the molecular and physiological mechanisms that underlie pheromone production and response in this species. The mandibular glands of queen honey bees produce a pheromone (QMP) which modulates many aspects of worker behavior and physiology, and is critical for colony social organization. Chapters 1 and 2 examine how the mating process in queens can produce changes in queen behavior, physiology, and pheromone production. Chapter 3 demonstrates that these changes in pheromone production appear to be linked to differences in ovary development, and that workers are most attracted to the pheromonal blend of queens with the most activated ovaries. Chapters 4 and 5 explore how variation in pheromone response can mediate queen-worker interactions. In chapter 4, I document extensive variation in worker attraction to QMP, show that this variation is linked to individual reproductive potential, and describe some of the molecular processes that are associated with this variation. Finally, in chapter 5, I test whether variation in a pheromone receptor for the main QMP component can explain the observed variation in worker attraction to the queen, and then take a molecular evolution approach to begin to elucidate the selection pressures acting on this receptor. In addition to the work presented in this dissertation, linkage mapping studies are currently underway to identify the genetic components underlying worker attraction to QMP as well as a set of behavioral and physiological manipulations to identify the epigenetic and environmental factors that can also contribute to this variation. The results of these studies demonstrate that the chemical communication system between honey bee queens and workers acts a dialog, rather than a simple, static signal-response system, and that variation in pheromone production and response both play a critical role in modulating queen-worker interactions within the hive.