Behaviour and Life History of a Large Carpenter Bee (Xylocopa Virginica) in the Northern Extent Ofits Range
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1 Behaviour and Life History of a Large Carpenter Bee (Xylocopa virginica) in the Northern Extent ofits Range by Sean Michael Prager, B.A. A Thesis submitted to the Department ofBiological Sciences in partial fulfilment ofthe requirements for the degree of Doctor ofPhilosophy Brock University St. Catharines, Ontario © Sean M. Prager, 2008 2 Abstract Large carpenter bees (Hymenoptera: Apidae: Xylocopa) have traditionally been thought ofas exhibiting solitary or occasionally communal colony social organization. However, studies have demonstrated more complex fonns ofsocial behaviour in this genus. In this document, I examine elements ofbehaviour and life history in a North American species at the northern extreme ofits range. Xylocopa virginica was found to be socially polymorphic with both solitary and meta-social or semi-social nests in the same population. In social nests, there is no apparent benefit from additional females which do not perfonn significant work or guarding. I found that the timing oflife-history events varies between years, yet foraging effort only differed in the coldest and wettest year of2004 the study. Finally, I that male X virginica exhibit female defence polygyny, with resident and satellite males. Resident males maintain their territories through greater aggression relative to satellites. 3 Ack'nowledgements A project likethis does not happen without the assistance ofthose who choose to contribute some oftheir intellectual fitness. I only hope they received some indirect fitness. Fiona Hunter was amazing in fighting for me and getting me to defence, I could not have done this without your aid. Jean Richardson provided advice, consul and many hours ofdata checking. To the other members ofmy committee: JeffStuart, Jon Middleton, Miriam Richards and early on Bob Caroline, your help is much appreciated. I would especially like thank the external reviewer for this thesis; Dr. Jon Barthell not only contributed his time and comments but also donated his bees. Numerous'field assistants helped observe and mark bees, without them this would have been difficult. Thank you to the machine shop for lending me tools and to physical plant for your varied assistance. Sandra Rehan and Amy Rutgers-Kelly, you both started as lab mates and have become great friends and comrades. Candice Kerling, there are countless ways in which I appreciate you and your karate kicking self. I would like to that thank'all those who have helped me by reading drafts. I would like to thank my friends; Canadian, American and other, you are all great. Finally, I would like to thank all the members ofmy family, immediate and extended, everyone ofyou has contributed to this in some way and I never could have done this without you. 4 Table of Contents Abstract 2 Ackn.owledgements 3 Table ofContents 4 List ofTables 8 List ofFigures 9 General Introduction......................................................................................................... 11 Hypothesis to explain the evolution ofaltruism 12 Kin selection 12 Mutualism 14 Queen control 14 Social organization in insects 15 Evolution ofeusociality in insects 17 Reproductive skew models 18 Subfamily Xylocopinae 20 Tribe Xylocopini 21 Genus Xylocopa 22 Subgenus Xylocopoides 22 Xylocopa virginica virginica 23 Aims ofthis research 24 General background and methods 26 Study sites-St. Catharines ' 26 Phenology and life cycle ~ 28 Bees obtained from other sources .., 30 Destructive sampling ofnests and collection ofcontents ~ 31 Paint marking for identification 33 Videoscope observations ofnests ;, 34 Observations offemales at nest entrances 35 Term.inology ,. 36 Chapter One: Foundress associations inXylocopa (Xylocopoides) virginica 37 Introduction 37 Methods 39 Nest contents and productivity 39 Brood parasites 40 Foundress survival and colonylongevity 41 Behavioural roles offemales 42 Comparisons offemales from multiple foundress nests 46 Statistical analyses 49 Results 50 Nest contents and productivity 50 Foundress survival and colony longevity 56 Behavioural roles offemales 57 Comparisons offemales from multiple-foundress nests 70 Behavioural comparisons 75 Discussion 80 5 The social organization ofXylocopa virginica 80 Adaptive significance ofsolitary versus multi-foundress nesting inXylocopa virginica 83 Broader implications ofXylocopa virginica social structure 86 Conclusions 88 Chapter Two: Relationships between nest architecture and behaviour inXylocopa virginica 90 Introduction 90 Methods 93 Study sites ·93 Nest architecture as it relates to brood laying order and size 93 The relationship between nest architecture and sex allocation 94 Relationships between nest architecture and parasitism 95 Relationships between nest architecture and number offemales 96 Sample availability considerations 97 Results 97 Relationships between nest architecture and brood 97 The relationship between nest architecture and sex allocation 98 Relationships between nest architecture and parasitism 98 Relationship between nest architecture and number offemales 103 Discussion .; ·... 106 Brood development and nest architecture............................................................... 106 Relationships between nests and sex allocation...................................................... 107 Relationships between parasitism and nesting .; 108 . Relationships between nests and social structure 109 Conclusions ;........................................... 111 Chapter Three: Annual variation in demography and activity ofXylocopa virginica in southern Ontario 112 Introduction 112 Methods 115 Study sites 115 Phenology and life cycle ofXylocopa virginica 115 Demographic indicators ofphenology 116 Analyses and quantification ofweather and climate trends 117 Relationships between weather and bee phenology 124 Evaluation offemale foraging effort....................................................................... 126 Annual variation in morphological size 128 Results 128 Phenology and life cycle ofXylocopa virginica 128 Demographic indicators ofphenology 132 Relationships between weather and bee phenology 137 Evaluation offemale foraging effort 137 Annual variation in morphological size 139 Discussion 142 Annual variation in phenology 142 Geographic variation in life cycle and phenology 143 6 Analyses offoraging effort 143 Weather and nest re-use 146 Taxonomic variation in phenology 147 Consequences ofpoor weather 148 Conclusions............................................................................................................. 149 Chapter 4: Male behaviour, mating tactics and aggression in association with female traits in the large carpenter bee,Xylocopa virginica 150 Introduction 150 Methods 153 Study Site 153 Marking for identification 153 Behavioural observations and censuses 153 Analytical Methods ' 157 Results......................................................................................................................... 162 Evidence for polygyn.y 162 Evidence ofterritoriality, resident and satellite males 162 Territorial vs. satellite male behaviour 169 Male-female interactions 171 Characteristics ofterritory quality 172 Discussion................................................................................................................... 177 Mating system in Xylocopa virginica 177 Behavioural differences between residents and satellites 178 Male-female interactions 179 Territory quality 181 Mating strategies in Hymenoptera 181 Conclusions............................................................................................................. 184 General Discussion and Conclusions.............................................................................. 185 Associations between males and females 185 Anomalous 2004 season 185 S·ociality in Xylocopa 186 A proposed sequence for the evolution ofsociality in Xylocopa 189 Further Research 193 Literature Cited 195 Appendices 208 Appendix 10: A descriptive and comparative study ofnest architecture in Xylocopa virginica 218 Introduction 218 Methods 218 Study sites, nesting site and substrate selection 218 Evaluation ofnest architecture 220 Results 223 Nesting site and substrate selection 223 Nest architecture 226 Geographic variation 231 Discussion 234 Nest site and substrate selection 234 7 Factors influencing nest architecture 236 Geographical variation in nest architecture 237 Interspecific variation in nest architecture in the genus Xylocopa 238 Conclusions 241 8 List of Tables Table I. 1: Explanation ofterminology used to describe various forms ofsocial organization. Summarized from Michener (1974) and Wilson (2000) 16 Table 1.1: Cross tabulation oftotal wear and reproduction measured as ovarian development 67 Table 1.2: Cross tabulation oftotal wear and reproduction measured as largest oocyte..69 Table 1.3: Cross tabulation ofthe expected relationships between work (wear) and reproduction (OD or largest oocyte) in females ofdifferent castes and forms ofsocial organization 81 Table 2.1: The developmental stage and sex ofbrood relative to its position within the nest ~ 99 Table 2.2: The effects ofnest architectural characteristics on the number offoundresses within a nest. 105 Table 3.1: .Summary ofweather conditions for the X virginica active season St. Catharines, Ontario for the years 2002-2006 and the 30-year mean 120 Table 3.2: Factor loading values for the first two principal components ofvariables related to weather 123 Table 3.3: The date ofimportant events in the X virginica life cycle in 2004-2006 130 Table