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Causes and Consequences of Variation in Immunity Within Insect

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Causes and Consequences of Variation in Immunity Within Insect Causes and consequences of variation in immunity within insect populations by Tonia Robb A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Biology Carleton University Ottawa, Ontario March 2006 © 2006, Tonia Robb Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Library and Bibliotheque et Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A 0N4 Ottawa ON K1A 0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-16674-1 Our file Notre reference ISBN: 978-0-494-16674-1 NOTICE: AVIS: The author has granted a non­ L'auteur a accorde une licence non exclusive exclusive license allowing Library permettant a la Bibliotheque et Archives and Archives Canada to reproduce,Canada de reproduire, publier, archiver, publish, archive, preserve, conserve,sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par I'lnternet, preter, telecommunication or on the Internet,distribuer et vendre des theses partout dans loan, distribute and sell theses le monde, a des fins commerciales ou autres, worldwide, for commercial or non­ sur support microforme, papier, electronique commercial purposes, in microform,et/ou autres formats. paper, electronic and/or any other formats. The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in et des droits moraux qui protege cette these. this thesis. Neither the thesis Ni la these ni des extraits substantiels de nor substantial extracts from it celle-ci ne doivent etre imprimes ou autrement may be printed or otherwise reproduits sans son autorisation. reproduced without the author's permission. In compliance with the Canadian Conformement a la loi canadienne Privacy Act some supporting sur la protection de la vie privee, forms may have been removed quelques formulaires secondaires from this thesis. ont ete enleves de cette these. While these forms may be includedBien que ces formulaires in the document page count, aient inclus dans la pagination, their removal does not represent il n'y aura aucun contenu manquant. any loss of content from the thesis. i * i Canada Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Parasitism is widespread, yet not all hosts appear to defend themselves against infection. The goal of my thesis was to highlight some consequences and in particular the causes of variation in insect immune expression. Costs of resistance against parasitism, particularly under environmentally relevant conditions will not only have consequences for host population dynamics but also may be related to whether or not resistance is expressed. My results suggest that likelihood of exposure to parasitism, the immune trait induced in response to parasitism, and in particular the likelihood of experiencing low temperatures best explains when the costs of resistance are realised under natural conditions. Researchers also have identified the relevance of temperature for the development of the parasite (costs of parasitism) and for host immune expression. Although I tested for other determinants of variation in resistance, my findings suggest that temperature likely accounted for the observed seasonal increases in resistance against parasitism for a damselfly-parasitic water mite association. Although not often examined, characteristics of the parasite also can influence resistance against parasitism. However, I found that timing influenced the ability of a water mite to attain parasitism on a damselfly host but not host resistance. Overall my studies on damselflies will contribute to a better understanding of how host sex, external factors such as temperature and biology of ectoparasitic mite larvae influence variation in insect immunity within host populations. Host density is thought to be important immune expression in insects, whereby greater allocation to immunity compensates for the density-dependent increases in host susceptibility to parasites. Many insects under high-densities also exhibit dark coloration - iii - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (greater cuticular melanism) which for these insects is associated with greater immunity. However, my results indicated that immunity is not associated with greater cuticular melanism in New Zealand mountain stone weta, a species where a genetic colour polymorphism occurs with no correlation to density. Thus, earlier findings of greater immunity associated with greater cuticular melanism in phase polyphenic insects cannot always be extended to insects with forms of discrete melanin variation. The novelty, salient findings and future directions as a result of this dissertation are also discussed. - IV - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS This dissertation would not have been possible without the help and support of my advisor Dr. Mark Forbes. His gentle encouragement to get the ‘papers out’ and advisement on what proposed projects could be completed was most appreciated. Mark also had a lot of patience in developing my writing and oral presentation skills. His kindness and support throughout my thesis work (and I’m sure for many years to come) has been greatly appreciated. There are also several members of the Forbes lab whom I would like to thank for their support during my thesis work. In particular Marc Lajeunesse helped out during my first year as prior to coming to the Forbes lab I had never completed any work with odonates. Although we got lost every time when Marc had to locate a pond or to find a particular damselfly species his help in the field and entertaining personality was most appreciated. I also thank Darryl Edwards (MSc), Dr. Selma Mautner (Post doc) and Dr. Pam Rutherford (Post doc). All were past Forbes lab members and were helpful in discussions of my experimental design. I am especially grateful to Pam for statistical help and the introduction to R, a free statistical/graphics package that I will likely use for the rest of my career. The current Forbes lab members also commented on the experimental design and general discussion of my thesis results during the ‘weekly’ Forbes lab meetings. The current members include Kathy Cook (now MSc), Yemisi Dare (PhD candidate), Kathryn Norman (MSc candidate), Stacey Robinson (S2, MSc candidate) and Paul Smith (PhD candidate). Through the years our Forbes lab meetings also had several ‘honorary’ lab members that contributed to our discussions. Arash Rashed (although he originally was a - v - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Forbes lab member) was especially useful in assessing whether the experiment would really answer the question (and was great to sit and have beer with). Other ‘honorary’ members include Chris Beatty (another great source of information and someone to have a beer with), Stacey Lee-Jenkins (SI because she arrived first) and Hans Van Gossum. Hans was especially helpful on damselfly life-history and we co-authored a short note together in Odonatologica, so thanks Hans for increasing my publication record. Most of my work either included field collections or field surveys and this would not have been possible without three great field assistants. Chrissy Belanger only helped out for a couple of weeks but I will always remember her for the sheer excitement when she caught a damselfly and in particular a ‘Nahini’ (couldn’t quite get the name Nahalenia- a damselfly species that I tended not to use but was quite plentiful). Silvia Laimgruber came all the way from Vienna, Austria to help me out in the field and I thank her for everything. Jamie MacDougall was my field assistant for two summers (although the second summer I had to let him go due to lack of damselflies to complete experiments on). Jamie was a great help in the field and the lab and provided some entertainment (thanks for ‘big blue’- the tape). All of the damselfly studies were completed at the Queen’s Biology Field Station. While working at the field station, I had tremendous help and support from Frank Phelan (manager). Again I thank Frank for all of his help and friendship even though he had to move the incubators and emergence traps several times for me. Frank’s kindness (and Euchre playing skills) made being at the field station just that much easier. Both Rod and Floyd Connor (assistant manager) were a great help while I spent four summers at the beautiful field station on Lake Opinicon. Bruce Smith (Ithaca College) was helpful in - vi - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. identification of the water mites and general discussion of some of my field projects. Kit Muma (Ithaca College) also was involved in some general discussion of my field projects as well as providing some help in finding various field sites when Lajeunesse could not remember them. I am forever grateful to Dr. James Fullard who shared lab space with me and allowed me to use his microscope. James also made coffee in the morning for the crew on several occasions (provided a new coffee maker too), fired up the BBQ for those ever important fish or casserole night BBQ’s (with the help of Kit Muma) and took the gang for ice cream and cheese curds. The weta study was completed in New Zealand and I thank Dr. Ian Jamieson for his part in this research project (both logistical and funding from University of Otago, and E.L. Hellaby Indigenous Grassland Research Trust to Ian Jamieson). For this project I had a lot of help in completing the field collections. Shelley Joyce, Craig Wilson, Jackie Tonbee, Rebecca Stevenson all helped with the collections. Shelley was my 4x4 driver and did a fine job of getting me to and from the field site.
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