Facultative Group Living in the Western Black Widow Spider, Latrodectus Hesperus: an Evolutionary Approach

FACULTATIVE GROUP LIVING IN THE WESTERN BLACK WIDOW SPIDER, LATRODECTUS HESPERUS: AN EVOLUTIONARY APPROACH by Maxence F. Salomon M.Sc. Swiss Tropical Institute, 2000 B.Sc. University of Geneva, 1999 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY In the Department of Biological Sciences © Maxence Salomon 2008 SIMON FRASER UNIVERSITY Spring 2008 All rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. 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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 included Bien 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. Canada APPROVAL Name: Maxence F. Salomon Degree: Doctor of Philosophy Title of Thesis: Facultative group living in the western black widow spider, Latrodectus hesperus: an evolutionary approach Examining Committee: Chair: Dr. R.A. Nicholson, Associate Professor Dr. B.D. Roitberg, Professor, Senior Supervisor Department of Biological Sciences, S.F.U. Dr. A.S. Harestad, Professor Department of Biological Sciences, S.F.U. Dr. R.G. Bennett, Seed Pest Management Officer B.C. Ministry of Forests Dr. W.P. Maddison, Professor Departments of Zoology and Botany, University of British Columbia Public Examiner Dr. J.A. Stamps, Professor Emeritus Section of Ecology and Evolution, University of California, Dayis External Examiner 4 April 2008 Date Approved ii SIMON FRASER UNIVERSITY SFU LIBRARY Declaration of Partial Copyright Licence The author, whose copyright is declared on the title page of this work, has granted to Simon Fraser University the right to lend this thesis, project or extended essay to users of the Simon Fraser University Library, and to make partial or single copies only for such users or in response to a request from the library of any other university, or other educational institution, on its own behalf or for one of its users. The author has further granted permission to Simon Fraser University to keep or make a digital copy for use in its circulating collection (currently available to the public at the "Institutional Repository" link of the SFU Library website <www.lib.sfu.ca> at: <http://ir.lib.sfu.ca/handle/1892/112>) and, without changing the content, to translate the thesis/project or extended essays, if technically possible, to any medium or format for the purpose of preservation of the digital work. The author has further agreed that permission for multiple copying of this work for scholarly purposes may be granted by either the author or the Dean of Graduate Studies. It is understood that copying or publication of this work for financial gain shall not be allowed without the author's written permission. Permission for public performance, or limited permission for private scholarly use, of any multimedia materials forming part of this work, may have been granted by the author. This information may be found on the separately catalogued multimedia material and in the signed Partial Copyright Licence. While licensing SFU to permit the above uses, the author retains copyright in the thesis, project or extended essays, including the right to change the work for subsequent purposes, including editing and publishing the work in whole or in part, and licensing other parties, as the author may desire. The original Partial Copyright Licence attesting to these terms, and signed by this author, may be found in the original bound copy of this work, retained in the Simon Fraser University Archive. Simon Fraser University Library Burnaby, BC, Canada Revised: Fall 2007 ABSTRACT A major goal of evolutionary research is to elucidate the processes involved in the evolution of group versus solitary living, by examining the selective forces driving or constraining a particular type of social system. Species with intermediate group living tendencies are particularly interesting because they offer insight into evolutionary transitions and, in particular, how different selective environments may modulate group living behaviours. This dissertation explores the different factors that shape the social strategies of the western black widow spider, Latrodectus hesperus, a facultatively group- living spider. Over a period of four years, I characterized the social structure of coastal British Columbia populations of L. hesperus, and show that individuals live either solitarily or in groups depending on the time of year, their reproductive status, and age. I then used an experimental approach to investigate the dynamics and adaptive value of facultative group-living behaviours, by testing different hypotheses about the decisions involved in social interactions, web building, microhabitat settlement, movement, and foraging. Several factors were manipulated and shown to influence the patterns of group living in L. hesperus, including individual nutritional state, prey availability, group size, population density, and neighbour proximity. Spiders adjusted their group living behaviours according to changes in these factors, and responded strategically to the presence and proximity of conspecifics. Based on the results of these experiments, I developed a model of group living in spiders that specifically considers the dynamic and strategic nature of social interactions in the context of frequency-dependent selection. The research presented in this thesis furthers our understanding of the evolution of social behaviour by providing new evidence on the mechanisms that promote and regulate facultative group-living behaviours. Keywords: aggregation; foraging; group living; social; spiders; web building in ACKNOWLEDGEMENTS First and foremost, I thank Bernie Roitberg for giving me the opportunity to conduct this project and for being an outstanding supervisor. His enduring trust and mentorship allowed me to flourish as a researcher and find my way through challenging times, and he was inspirational. I also thank Robb Bennett for his keen support and mentorship, for sharing his passion of spider biology, and for welcoming me into his home. I thank Alton Harestad for all of his feedback and advice throughout this project and for his enthusiasm. I also thank Judy Stamps and Wayne Maddison for reading my dissertation and providing a lot of constructive criticism and ideas. Samantha Vibert provided invaluable help and advice during all phases of this project and her contribution was instrumental to the success of most of this research, as was her close friendship. I also thank all the members of the Roitberg lab from 2002- 2008 for providing such a stimulating research environment. I thank Clea Moray for patiently sharing her knowledge of scientific writing and computer programming. I thank Gwylim Blackburn for a lot of helpful discussions, and also good times in the field. The Bennett-Terpenning family have improved my quality of life by providing generous hospitality and much support during deamnding times. I thank Sarbjeet Mann for her patience and love, which no doubt helped me complete this project. I thank Nick Charette, Angela Mah, Carolyn Duckham, Nadia Brinkman, Melanie Hart, Coltilde Salomon, Jason Peterson and Gwylim Balckburn for assistance in the field and laboratory. I also thank numerous co-workers and friends for intellectual input and help, namely Jay Biernaskie, Richard Ring, Bruce Leighton, David Green, Laurie Marczak, Deepa Pureswaran, Dave Gillespie, Ian Gordon, Peter Midford, Gerta Moray, Gerhard and Regine Gries, various members of the Gries lab, Larry Dill, Heather Higo, IV Scott Pavey, Peter Belton, Dave Raworth, Kefyn Catley, Carl Schwarz, Nadia Sartoretti, Nick Page, Patricio Salazar and Esperanza, PatrikNosil, Marcela Olguin, Andres Valle- Domenech, the BISC technicians, various TA instructors and

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