THE BEHAVIOURAL ECOLOGY OF TROPHIC EGG-LAYING Jennifer C. Perry B.Sc. (Hon.) Environmental Biology, University of Alberta, 2001 Thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE In the Department of Biological Sciences O Jennifer C. Perry 2004 SIMON FRASER UNIVERSITY July 2004 All rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. 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 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. 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. Bennett Library Simon Fraser University Burnaby, BC, Canada ABSTRACT Across diverse taxa, animals produce infertile trophic eggs that are consumed by offspring. The objective of this thesis research was to establish a behavioural ecology framework for the study of trophic eggs; to model their evolution; and to investigate their adaptive function, if any, in the ladybird beetle Harmonia axyridis. Current trophic egg hypotheses suggest two adaptive functions: provisioning offspring or reducing parent-offspring conflict over sibling cannibalism. On the other hand, trophic eggs may simply represent infertility - they may not be an adaptation at all, a distinction given insufficient attention in the literature. I consider trophic egg laying in the context of sibling cannibalism behaviour. A frequency-independent analysis of sibling cannibalism suggests that there is a critical value of increase in offspring survival above which cannibalism benefits both parents and offspring; then mothers should adopt tactics (e.g., trophic egg laying) to facilitate cannibalism. However, the frequency-independent approach does not incorporate game interactions. I used a genetic algorithm approach to model the co-evolution of trophic eggs, sibling cannibalism, and hatching synchrony. Results suggest that, when game interactions occur or when infertile eggs are present, cannibalistic tendencies increase dramatically, as does the maternal response to limit cannibalism. Furthermore, trophic egg laying and hatch synchrony appear to be viable tactics for facilitating egg-eating. We tested trophic egg function in H. axyridis, predicting that mothers should lay fewer trophic eggs in food-rich environments and more in low food environments where offspring gain a larger relative benefit from eating an egg. As predicted, ladybirds produced 64% more trophic eggs when provided with information that they were in a low vs. high food environment (P = 0.0093). This result demonstrates that ladybirds produce trophic eggs to increase the chance that offspring survive starvation. In a second observation set, I tested whether the spatial distribution and oviposition sequence pattern of trophic eggs is over- or under-dispersed compared to random. There was no indication of a non-random distribution. In conclusion, this research is of interest in behavioural ecology because it shows that an unusual parenting strategy, killing off some offspring to benefit others, can be adaptive. Acknowledgements First and foremost, I thank the members of my supervising committee - Dr. Bernie Roitberg, Dr. Bernie Crespi and Dr. Felix Breden - for their carefully considered advice as I prepared for and conducted this thesis research. 1 particularly appreciate the guidance and mentorship of my senior supervisor, Bernie Roitberg, throughout this project. I am grateful to Dr. Carl Schwarz, who provided extremely useful statistical help, and Jabus Tyerman, who wrote the randomisation test program described in Chapter 4. The manuscripts were improved by thoughtful and appreciated comments from Geoff Allen, Jay Biernaskie, Felix Breden, Kelly Campbell, Bernie Crespi, Brian Ma, Jason Peterson, Bernie Roitberg, Maxence Salomon, and Jabus Tyerman. I am obliged to laboratory assistants Andy Capadouca, Nick Charrette, Beth Ann Nyboer, Jennifer O'Neil, Eva Poon, and Andy Yang, for their assistance. Members of the Behavioural Ecology Research Group, the Entomological Society of British Columbia, and the DOGG Journal Club provided helpful advice as I planned and conducted experiments. The research was supported by the National Science and Engineering Research Council (NSERC) in graduate support and grants to Bernie Roitberg. I also acknowledge graduate support from the Department. Finally, I must express my appreciation for the Roitberg lab group. Frequent discussions with Roitbergers improved all aspects of this work, and lab interactions made this research process tremendously enjoyable. Table of Contents .. Approval ...................................................................................................................................11 Abstract ................................................................................................................................. nl... Acknowledgements ........................................................................................................................iv Table of Contents ...........................................................................................................................v List of Figures ...............................................................................................................................vu .. List of Tables .................................................................................................................................ix Chapter 1 Overview of the Thesis ..........................................................................................1 Overview ....................................................................................................................1 Literature Cited ..........................................................................................................3 Chapter 2 The Behavioural Ecology of Trophic Egg Laying: Hypotheses and Evidence ...................................................................................................................4 Abstract ......................................................................................................................4 Introduction ................................................................................................................4 Parent and offspring interests: inclusive fitness approach .........................................5 Two sets of trophic egg hypotheses ...........................................................................7 The parent-offspring conflict reduction hypothesis ...........................................8 Cooperation hypothesis ..........................................................................................9 What evidence is required to distinguish hypotheses? .............................................10 Evidence from natural history and behavioural observations .............................. 11 Evidence from behavioural and life history experiments .....................................11 Comparative analyses........................................................................................... 13 Challenges for future research ................................................................................. 14 Conclusions ..............................................................................................................15 Literature cited ......................................................................................................... 17 Chapter 3 Co-Evolution of Maternal and Offspring Effectors of Sibling Cannibalism ........................................................................................................... 31 Abstract ....................................................................................................................31 Introduction .............................................................................................................. 31 Model ....................................................................................................................... 33 Biological system ..........................................................................................33 Inclusive fitness argument .................................................................................... 34 Genetic algorithm-based simulations: the basic model ........................................ 35 Computer experiments ......................................................................................... 36 Results and discussion .............................................................................................38 Relative benefit of egg eating .............................................................................. 38 Trait co-evolution .................................................................................................40