xii, 109 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / There are two fundamental environmental rhythms that organisms in nature encounter: (1) the daily rhythm of light and dark that is due to the rotation of the earth about its axis and (2) the yearly seasonal rhythm due to the angle of the earth's rotation relative to the plane of its orbit around the sun. All eukaryotes have an endogenous circadian (daily) clock that allows for the timing of biological events within the context of the daily light:dark cycle. A wide diversity of plants and animals in temperate regions use photoperiodic (daylength) cues to time life history events, such as reproduction and diapause (insect dormancy) within the context of the yearly seasonal cycles. This dissertation focuses on the relationship between the circadian clock, photoperiodic time measurement and diapause. Chapter I serves as an introduction to biological timing and briefly summarizes the chapters that follow Chapter II outlines why Drosophila melanogaster , the workhorse of modern insect genetics, is not an appropriate system for the study of photoperiodism. Chapter III defines the Nanda-Hamner response, the circadian phenotype used in this dissertation, and proposes that the NH response is due to a rhythmic level of circadian disorganization in response to environmental cycle length. Chapters IV and V deal primarily with the long-held proposition that the circadian clock forms the causal basis of photoperiodic time measurement. I show that variation in the circadian clock does not covary with photoperiodic phenotypes among natural populations of Wyeomyia smithii , and thus these two processes are evolutionarily independent. Chapter VI describes the first forward genetic screen for candidate genes involved in photoperiodism and diapause termination in any animal. Chapter VII is a discussion of the complexity involved in studies of the genetics of photoperiodism and diapause and how historical inertia of scientific hypothesis acts to confound, rather than clarify, the relationship between genotypes and phenotypes. Chapter VIII is a concluding discussion of the implications of the work presented. This dissertation includes both previously published and co-authored material. / Committee in charge: William Cresko, Chairperson, Biology; William Bradshaw, Advisor, Biology; Patrick Phillips, Member, Biology; Eric Johnson, Member, Biology; Stephen Frost, Outside Member, Anthropology

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20954号 / 理博第4406号 / 新制||理||1633(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 沼田 英治, 准教授 森 哲, 教授 中川 尚史 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

To persist in extreme environments, some meiofaunal taxa have adopted outstanding resistance strategies. Recent years have seen increased enthusiasm for understanding extreme-resistance mechanisms evolved by tardigrades, nematodes and rotifers, such as the capability to tolerate complete desiccation and freezing by entering a state of reversible suspension of metabolism called anhydrobiosis and cryobiosis, respectively. In contrast, the less common phenomenon of diapause, which includes encystment and cyclomorphosis, is defined by a suspension of growth and development with a reduction in metabolic activity induced by stressful environmental conditions. Because of their unique resistance, tardigrades and rotifers have been proposed as model organisms in the fields of exobiology and space research. They are also increasingly considered in medical research with the hope that their resistance mechanisms could be used to improve the tolerance of human cells to extreme stress. This review will analyse the dormancy strategies in tardigrades, rotifers and nematodes with emphasis on mechanisms of extreme stress tolerance to identify convergent and unique strategies occurring in these distinct groups. We also examine the ecological and evolutionary consequences of extreme tolerance by summarizing recent advances in this field.

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The purpose of this study was to begin a study characterizing the diapause state in Sarcophaga crassipalpis. Recent evidence suggests the diapause syndrome is a unique developmental state with its own set of genes expressed. Two cDNA libraries from the pupal brains of diapausing and nondiapausing S. crassipalpis were generated. These libraries will be the basis for future work determining the expressed and repressed genes during the diapause syndrome. The genetic regulation of diapause in S. crassipalpis is also of interest. This species enters diapause during metamorphosis, which is under regulation of the steroid hormone 20-hydroxyecdysone (20-HE). Because the metamorphic system is suspended for diapause in this species, whether or not the EcR is expressed in the diapause state is of interest. To address this issue, a partial EcR was cloned from S. crassipalpis by RT-PCR. This partial EcR was found in all developmental stages tested.

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The La Crosse virus (LACV) is an emerging pathogen in the Appalachian region of the United States. The virus maintains a complex natural cycle through horizontal transmission with sciurid rodents and Aedes mosquitoes in Virginia. Transovarial transmission also occurs in this host-parasite system and has evolved for the virus to persist through winter. The virus perpetuates in diapause induced embryos and infects naive rodents the following spring. As global temperatures rise, it is imperative we evaluate how the virus and its vectors overwinter. We conducted experiments to evaluate and determine the diapause induction, or prediapause stage, in Aedes japonicus japonicus, and the ecophysiology and low temperature biology of how LACV affects Aedes triseriatus and Aedes albopictus embryos at low temperatures. We found that the prediapause stage of Ae. j. japonicus is the maternal stage, the developing adult female that lays diapause eggs. This more closely resembles Ae. albopictus and not Ae. triseriatus. As measured in the field and laboratory, LACV has a clear negative effect on the ability of Ae. triseriatus and Ae. albopictus to survive the winter. There was no major effect of LACV infection on the ability of these two species to enter diapause or their critical photoperiods, but there was a significant negative effect of LACV infection on survivorship of embryos that were placed in their natural habitat and in their susceptibility to low temperatures. LACV infection had a more significant negative effect on Ae. albopictus than on Ae. triseriatus and suggests that Ae. albopictus is a subordinate vector relative to Ae. triseriatus in the maintenance of the virus over the winter season. Our findings highlight the need for the increased surveillance of LACV as temperatures continue to rise due to climate change. / PHD / In Virginia, mosquitoes may transmit the La Crosse virus (LACV) that can cause swelling of the brain in humans. This virus infects mosquitoes which is then transmitted to chipmunks. When a mosquito bites an infected chipmunk and then bites a human, the virus be transmitted to the human. Adult female mosquitoes can also pass the virus on to their developing offspring, which is the way it is maintained throughout the winter. Certain infected mosquitoes will spend the winter as eggs and the mosquitoes that hatch carry the virus and can infect chipmunks the following spring. The experiments conducted here looked at how one mosquito that can spread the LACV begins the process to survive the winter. We also did experiments to look at how the virus affects two other mosquito’s ability to begin the same process and then if they can survive the winter and cold temperatures while infected. We found that the Asian Bush Mosquito enters diapause in a different way than we suspected by the female mosquito sensing shorter days at the end of the summer; at this point she will then lay eggs that survive the winter. We discovered that viral infection will hurt the chances of the Asian Tiger Mosquito and Eastern Tree-hole Mosquito to survive the winter. We also found that virus-infected mosquitoes cannot survive temperatures as lower than those that are not infected. This means that the risk of the virus to humans can be greater as temperatures rise due to global warming.