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Understanding Avian Plasmodium Distribution: the Role of Vector and Host

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Understanding Avian Plasmodium Distribution: the Role of Vector and Host UNDERSTANDING AVIAN PLASMODIUM DISTRIBUTION: THE ROLE OF VECTOR AND HOST A Dissertation Presented to the Faculty of the Graduate School of Cornell University In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Mari Kimura August 2008 © 2008 Mari Kimura UNDERSTANDING AVIAN PLASMODIUM DISTRIBUTION: THE ROLE OF VECTOR AND HOST Mari Kimura, Ph.D. Cornell University 2008 Malaria parasites have a complex life cycle involving sexual reproduction in the mosquito vector and asexual proliferation in the vertebrate host. Mosquito vectors are therefore the definitive host of the malaria parasite. The literature on avian malaria parasites remains biased towards bird-parasite associations, and avian malaria vectors are not well studied in this system. My dissertation fills a gap in the current body of avian malaria research by using molecular techniques to document 1) patterns in phylogeographic structure of avian Plasmodium across geographic regions; 2) absence of vector specificity in two common mosquito species in Ithaca, New York; and 3) evidence that local vectors amplify a local avian Plasmodium lineage. In my first chapter, I review our current understanding about the associations between avian malaria vectors and avian Plasmodium. I synthesize this with literature on human malaria-mosquito interactions and mosquito feeding preferences to argue that it is crucial to study vector ecology to understand host-parasite dynamics. Variation in mosquito ecology could help explain patterns observed in avian malaria parasite infection. In chapter 2, I document patterns of phylogeographic structure in Plasmodium parasites sampled across the range of a single bird species. I demonstrate that geographic patterns in parasite lineage distribution are not solely attributable to differences in the parasites found in different bird species. In chapter 3, I describe the avian Plasmodium lineages found in two abundant, local ornithophilic mosquito species and show that parasites sampled from mosquitoes are represented by many diverse cytochrome b haplotypes. The most common of these haplotypes are shared between mosquito species, and overlap only slightly with those previously isolated directly from numerous bird species. In chapter 4, I report results from a feeding experiment using laboratory-reared mosquitoes and wild-caught birds naturally infected with Plasmodium. I examine the variation within Cx. pipiens in its ability to be invaded by the parasite by conducting PCR on individual mosquitoes following incubation with sufficient time to allow the complete digestion of the blood meal and development of sporozoites in the salivary glands. BIOGRAPHICAL SKETCH Mari Kimura was born in New York, NY and spent the first 22 years of her life in the city. She studied English literature at Columbia University as an undergraduate from 1984-1988. She chose not to pursue a career in this field, so she decided to move out west in search of adventure and something more satisfying to do with her life. She arrived in San Francisco two weeks before the 1989 earthquake and stayed until 2002. During this time she had many outdoor adventures, worked at the Natural Resources Defense Council, and became interested in biology. Her first field assistant job involved camping on an island in British Columbia conducting orca surveys. A few years later, she assisted in hornbill research at a remote rainforest site in the Dja Reserve, Cameroon. She decided to pursue a graduate degree in biology and spent several years taking prerequisite science courses in the Bay Area while moonlighting at corporate law firms. She received her master’s degree in Ecology and Systematics in 2002 from San Francisco State University under Dr. Thomas B. Smith. Her master’s research explored the phylogeography of Wilson’s warblers across both their breeding and wintering areas. It was at this time that she started to work with Dr. Irby Lovette, who was a postdoc while she was a master’s student. She was so impressed with Irby that she followed him to Cornell as his first graduate student. She originally thought that she would continue studying migratory warblers when she embarked on her doctoral research. Research tends to take on a life of its own, however, and she soon found herself fascinated by the mystery of avian Plasmodium and its mosquito vectors, which eventually became the topic of her dissertation. iii ACKNOWLEDGMENTS My three committee members contributed equally to my dissertation research and development as a scientist. I thank them for many stimulating discussions and for being completely available to me at all times. Dr. Laura Harrington introduced me to the field of medical entomology and taught me everything I know about mosquitoes. Her wealth of knowledge and natural ability to motivate students inspired me to continue with my research, especially during the difficult times. She was my true thesis supervisor as my project moved farther away from birds and closer to mosquitoes. Dr. André Dhondt has an amazing, creative mind. He taught me how to think like a scientist and steered me to locate gaps in our current knowledge and to try to fill those gaps by asking well-framed questions. Dr. Irby Lovette raised the bar for the quality of my work and relentlessly kept me on schedule. I am grateful for the lightning speed with which he returned comments on my drafts, and for his heartfelt encouragement when I did a good job. His pushiness and rigor, while maddening at times, ultimately made me a stronger and more responsible student and may have cured me of my chronic procrastination habits forever. Many other people contributed to my research over the years: Ravinder Sehgal for intellectual camaraderie, Ellis Greiner for parasitological expertise, Wesley Hochachka for great feedback delivered with dry wit, the Evo Bio Big Kids and the Dhondt lab group for bouncing ideas around, and Keila Seidenstrycker for guidance on captive birds. For help and guidance in the lab and with samples: Amanda Talaba, Laura Stenzler, Caitlin McKenna, Becky Poulson, Rachel Hathaway, Dana Hawley, Jon Darbro. My parents were constantly supportive. Finally, I could not have asked for a more amazing circle of graduate students who will remain lifelong friends. I thank them for their support and for countless fun-filled times over the last six years. iv TABLE OF CONTENTS BIOGRAPHICAL SKETCH..................................................................................... iii ACKNOWLEDGMENTS......................................................................................... iv LIST OF FIGURES ................................................................................................. vii LIST OF TABLES.................................................................................................. viii PREFACE ................................................................................................................ ix CHAPTER 1. THE IMPORTANCE OF VECTOR ECOLOGY IN AVIAN MALARIA HOST-PARASITE DYNAMICS............................................... 1 Introduction............................................................................................................ 1 Background............................................................................................................ 2 Evidence for Plasmodium coevolution with hosts................................................... 6 Evidence for Plasmodium coevolution with vectors................................................ 7 Importance of vectors in an ecological context ....................................................... 9 The vector-host interaction: host feeding preference.............................................12 Effects of bird behavior on host preference............................................................15 Effects of habitat choice on host preference...........................................................16 Mosquito phenology and temporal patterns of Plasmodium lineage distribution ....17 Conclusions and future directions..........................................................................18 CHAPTER 2. PHYLOGEOGRAPHIC STRUCTURING OF PLASMODIUM LINEAGES ACROSS THE NORTH AMERICAN RANGE OF THE HOUSE FINCH (CARPODACUS MEXICANUS).........................31 Abstract.................................................................................................................31 Introduction...........................................................................................................32 Materials and methods...........................................................................................34 Results ..................................................................................................................36 Haematozoan prevalence...................................................................................36 Haematozoan cytochrome b sequences..............................................................36 Patterns of nucleotide substitutions among haplotypes.......................................37 Distribution of Plasmodium haplotypes among house finch populations............38 Discussion.............................................................................................................39 CHAPTER 3. AVIAN MALARIA PARASITES SHARE CONGENERIC MOSQUITO VECTORS.................................................................48 Abstract.................................................................................................................48
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