Nosema and Necrophoresis: a Honey Bee Parasite and Undertaking
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NOSEMA AND NECROPHORESIS: A HONEY BEE PARASITE AND UNDERTAKING BEHAVIOUR by Megan J. Colwell Thesis submitted in partial fulfillment of the requirements for the Degree of Bachelor of Science with Honours in Biology Acadia University March, 2010 © Copyright by Megan J. Colwell, 2010 This thesis by Megan J. Colwell is accepted in its present form by the Department of Biology as satisfying the thesis requirements for the degree of Bachelor of Science with Honours Approved by the Thesis Supervisor __________________________ ____________________ Dave Shutler Date Approved by the Head of the Department __________________________ ____________________ Soren Bondrup-Nielsen Date Approved by the Honours Committee __________________________ ____________________ Sonia Hewitt Date ii I, MEGAN J. COLWELL, grant permission to the University Librarian at Acadia University to reproduce, loan or distribute copies of my thesis in microform, paper or electronic formats on a non-profit basis. I, however, retain the copyright in my thesis. _________________________________ Signature of Author _________________________________ Date iii Acknowledgements First and foremost I would like to thank Dave Shutler, my supervisor and mentor for the last year. Without his invaluable shredding of my writing, insights into new and exciting project prospects, his ability to understand what direction I wanted to take, and most importantly his sense of humour, this past year would have been dreadful. Also thank-you to the graduate students of Team Shutler, especially Geoff Williams, for welcoming me into the lab and sharing their knowledge and experience. A special thank-you to my fellow Honours students: my lab mates, Holly Lightfoot and Emma Vaasjo, and my office mates, Emma McIntyre and Laura Ferguson. I would also like to thank Adele Mullie for her part in “string theory”, and for tolerating the presence of my skunk-addled bees on the Mullie-Shutler property this summer. Thank-you to Jack and Lorraine Hamilton for letting me deploy my dead bee trap and abscond with some of their bee corpses in Aylesford, and Kevin Spicer and Don Amirault for providing colonies in Coldbrook. I would like to thank all the professors, faculty, and Lisa Taul of the Department of Biology for their help and advice over the past four years, particularly Glenys Gibson for serving on my oral committees and offering so many great recommendations. Finally, I would like to thank my friends and family for all their support and interest in my work. iv Table of Contents List of Tables .................................................................................................................vi List of Figures ...............................................................................................................vii Abstract....................................................................................................................... viii Chapter I: Prophylactic behaviours in eusocial insects ....................................................1 Chapter II: Nosema and necrophoresis: a honey bee parasite and undertaking behaviour ........................................................................................................................7 Methods.......................................................................................................................9 Results.......................................................................................................................12 Discussion .................................................................................................................13 References.....................................................................................................................17 Appendix I: Tables .......................................................................................................21 Appendix II: Figures.....................................................................................................23 v List of Tables Table 1. There was no significant correlation between drop distance in Aylesford or Coldbrook and log of (Nosema per bee +1), including non-infected corpses............................21 Table 2. There was no significant correlation between drop distance in Coldbrook and drop distance in Aylesford including non-infected corpses, whether corpses were originally from Aylesford or Coldbrook. ........................................................................................21 vi List of Figures Fig. 1. Position of a dead bee trap on a pallet-raised colony. .........................................23 Fig. 2. Skunk blocker on a pallet-raised colony.............................................................23 Fig. 3. Marking locations of paint (a) and string (b) on worker corpses. ........................24 Fig. 4. There was no significant correlation between drop distance in Aylesford and log of (Nosema per bee +1)..............................................................................................24 Fig. 5. There was no significant correlation between drop distance in Coldbrook and log of (Nosema per bee +1)..............................................................................................25 Fig. 6. There was no significant correlation between drop distance in Coldbrook and log of (Nosema per bee +1), whether corpses were originally from Aylesford or Coldbrook. ..............................................................................................................................26 Fig. 7. There was no significant correlation between of drop distance in Coldbrook and drop distance in Aylesford. ............................................................................................27 Fig. 8. There was no significant correlation between drop distance in Coldbrook and drop distance in Aylesford, whether corpses were originally from Aylesford or Coldbrook. ..............................................................................................................................28 vii Abstract European honey bees ( Apis mellifera ) live in closed colonies at high densities with genetically-related individuals (mostly sisters) in constant high temperatures and humidity, making disease prevention a necessity. Undertakers are a specialist group of honey bee workers that remove dead bees from the hive (necrophoresis), presumably to restrict the spread of pathogens. Nosema ceranae is an emerging fungal parasite of the European honey bee, and is a serious threat to hive health. The first objective of this study was to test if undertakers distinguished among corpses with different intensities of Nosema -infection. The second objective was to test if undertakers treated corpses consistently in consecutive removals from colonies. Dead bee traps (2 m x 1 m) were used to collect corpses that had been uniquely marked with paint or string. I recorded distances at which corpses were dropped from a hive (drop distance), redeployed them in a second hive, and again recorded drop distances. N. ceranae infection intensity was quantified in recovered corpses. There was no significant correlation between drop distance and N. ceranae intensity. There was also no significant relationship between the initial and subsequent drop distance of corpses experimentally re-introduced to hives. These results suggest that necrophoresis is not pathogen-driven. However, observations suggest a new hypothesis that drop distance depends on how corpses are carried and whether they get tangled with undertakers. This could be investigated by studying how undertakers grasp corpses, how undertakers drop corpses, and how undertakers become tangled with corpses. viii CHAPTER I: PROPHYLACTIC BEHAVIOURS IN EUSOCIAL INSECTS Some colony-living insects are divided into castes of sterile and reproductive individuals. Such insects are called eusocial. Reproductive members are queens and usually many male drones, with the remainder of females acting as sterile workers. Two more characteristics of eusocial insects include living in colonies in which there are two or more overlapping generations, and cooperative care for young (Wilson and Hölldobler 2005). In bees, is determined in a system called haplodiploidy, in which eggs laid by a queen that are fertilized develop into females, and those not fertilized develop into males. Haplodiploidy is believed to be one of the significant factors that drove the evolution of eusociality. Because females get genetic material from both a mother and father, the average relationship between worker sisters is closer to each other than to their own potential offspring (which would likely not be fertilized), facilitating the development of altruistic behaviour in eusocial insects (Linksvayer 2005). Eusociality has numerous benefits which decrease costs of brood-raising, foraging, and defence (Wilson-Rich et al. 2009). Another aspect of eusociality is the further separation of sterile members into castes based on division of labour. In this system, workers perform only a subset of the entire range of tasks done in the colony, and this subset of activity varies among groups of workers (Beshers and Fewell 2001). Division of labour can be based on morphological or ontogenetical differences; the latter is division of workers into tasks based on their age (temporal polyethism), and, by the nature of these tasks, also a spatial division. Younger individuals tend to perform tasks in the innermost area of the colony (intranidal), middle- aged on the periphery,