A University of Sussex PhD thesis Available online via Sussex Research Online: http://sro.sussex.ac.uk/ This thesis is protected by copyright which belongs to the author. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Please visit Sussex Research Online for more information and further details UNIVERSITY OF SUSSEX Submitted for the Degree of Doctor of Philosophy VICTORIA CATHERINE NORMAN Caste and Task Allocation in Ants SUMMARY Group living is a widely adopted strategy by many organisms and given the advantages offered by a social lifestyle, such as increased protection from predators or increased ability for resource exploitation, a wide variety of animals have adopted a social lifestyle. Arguably none have done this more successfully than the social insects. Indeed their efficient division of labour is often cited as a key attribute for the remarkable ecological and evolutionary success of these societies. Within the social insects the most obvious division of labour is reproductive, in which one or a few individuals monopolise reproduction while the majority of essentially sterile workers carry out the remaining tasks essential for colony survival. In almost all social insects, in particular ants, the age of a worker will predispose it to certain tasks, and in some social insects the workers vary in size such that task is associated with worker morphology. In this thesis I explore the proximate and ultimate causes of worker and reproductive division of labour in ant societies, which span a range of social complexities. I predominantly focus on both the highly derived leaf-cutting ants – a so-called ‘pinnacle’ of evolution within the social insects, with a complex division of labour and a strong worker caste system – and in the more basal primitive societies of the queenless ponerine dinosaur ants, which can offer an insight in to the evolution of division of labour at the earliest stages of social lifestyles. This work demonstrates the environmental and genetic determinants of division of labour in group-living societies outside of the classical honey bee model system. This is important as it helps us to better understand the broader processes shaping behaviour and phenotype in the animal kingdom. i Caste and Task Allocation in Ants Victoria Catherine Norman Submitted for the Degree of Doctor of Philosophy University of Sussex Faculty of Life Science July 2016 ii Declaration I confirm that the work submitted is my own, except where work which has been formed part of jointly-authored publications is included. The contributions of other authors are indicated for published chapters listed below. This thesis has not been and will not be submitted to another institution for the award of any other degree. List of published chapters and contributions: Chapter 2. Norman, V. & Hughes, W.O.H. 2016. Behavioural effects of juvenile hormone and their influence on division of labour in leaf-cutting ant societies. Journal of Experimental Biology. 219: 8-11. VN and WOHH designed the experiments, VN carried out the experiments and analysed the data and wrote the manuscript. WOHH aided in the manuscript writing. Chapter 3. Norman, V., Pamminger, T. & Hughes, W.O.H. 2016. The ambiguous role of juvenile hormone in regulating reproductive physiology but not dominance hierarchy in Dinoponera quadriceps. Behavioural Ecology and Sociobiology (in review) VN, TP and WOHH designed the experiments, VN carried out the experimental work, TP carried out dissections, VN and TP analysed the data and wrote the manuscript. WOHH aided in the manuscript writing. iii Chapter 4. Norman, V., Hoppé, M. & Hughes, W.O.H. 2015. Old and wise but not size: factors affecting threat response behaviour and nestmate recognition in Acromyrmex echinatior leaf-cutting ants. Insectes Sociaux. 61: 289-296 VN and WOHH designed the experiments. VN carried out the experimental work, analysed the data and wrote the manuscript. WOHH and MH aided in the manuscript writing. Chapter 5. Norman, V., Butterfield, T., Tasman, K., Drijfhout, F. & Hughes, W.O.H. 2016 Alarm pheromone composition and behavioural activity in fungus growing ants. Journal of Chemical Ecology (in review). VN and WOHH designed the experiments. VN carried out the experimental work, analysed the data and wrote the manuscript. TB and FD provided technical assistance for chemical work. KT carried our preliminary behavioural trials. WOHH aided in the manuscript writing. Chapter 6. Norman., V., Pamminger, T. & Hughes, W.O.H. 2016. The effects of disturbance threat of leaf-cutting ant colonies: a laboratory study. Insectes Sociaux (in press). VN and WOHH designed the experiments. TP carried out immunity assays. VN carried out all other experimental work, analysed the data and wrote the manuscript. WOHH aided in the manuscript writing. iv Chapter 7. Norman, V., Darras, H., Tranter, C., Aron, S. & Hughes, W.O.H. 2016. Cryptic lineages hybridize for worker production in the harvester ant Messor barbarus, Biology Letters (in press). WOHH, VN, HD and SA conceived and planned the study. VN, CT and HD collected samples. VN and HD performed molecular work and analysed the data. VN and HD drafted the manuscript. All authors helped draft the final manuscript and gave approval for publication. Chapter 8. Norman. V., Pamminger, T. & Hughes, W.O.H. 2016. Behavioural development, fat reserves and their association with productivity in Lasius flavus founding queens. The Science of Nature. 103: 3-4. VN and TP designed the experiments. VN carried out all experimental work, analysed the data and wrote the manuscript. TP and WOHH aided in the manuscript writing. Chapter 9. Norman, V.C., Pamminger, T., F. Nascimento & Hughes, W.O.H. 2016. Simple societies and personalities: behavioural consistency, syndromes and association with rank in the primitively eusocial Dinoponera quadriceps. Ethology (in review) VN, TP and WOHH designed the experiments. VN carried out the experimental work, analysed the data and wrote the manuscript. FN assisted with field work. TP and WOHH aided in the manuscript writing. Signed: _______________________ Date:______________ v Acknowledgements Firstly, thank you to Bill Hughes for the opportunity to undertake this PhD. I have found it a fully rewarding and fantastic way to spend four years of my life. Thank you for your support throughout this research and, most importantly, the opportunity to dig holes in multiple countries. Thank you to the rest of the Hughes lab in its various guises. To Julia: thank you for all the caffeine, advice and friendship. Tobias and David – thank you for the countless discussions about ants (and for feeding my ants more times than I can remember). To Christopher Tranter for putting up with me on fieldwork, making me laugh, and for letting me drag you out biking. Thank you to the rest of the lab members that have come and gone over the last few years: Georgia, Rosaline, Joanne, as well as the many others from LASI: Kyle, Tom, Alan, Luciano, Nick and Hasan to name a few. Thank you for your input in to this work, and for making it immeasurably easier and more fun. To my family, thank you for supporting me no matter what I have chosen to do. It often goes unsaid, but I am truly thankful. I would also like to say a massive thank you to Margaret Couvillon, Roger Schürch and Gianluigi Bigio. You made me feel instantly at home from the day I moved to Brighton and have been like a second family to me. Thank you for the endless laughter, the talks about science, and for the beef on my pillow. Lastly, but most importantly, thank you to David Topham. I am ever grateful for your constant support through the highs and lows, for your infinite patience, and for always making me smile. Here’s to many more adventures together. vi Abstract Group living is a widely adopted strategy by many organisms and given the advantages offered by a social lifestyle, such as increased protection from predators or increased ability for resource exploitation, a wide variety of animals have adopted a social lifestyle. Arguably none have done this more successfully than the social insects. Indeed their efficient division of labour is often cited as a key attribute for the remarkable ecological and evolutionary success of these societies. Within the social insects the most obvious division of labour is reproductive, in which one or a few individuals monopolise reproduction while the majority of essentially sterile workers carry out the remaining tasks essential for colony survival. In almost all social insects, in particular ants, the age of a worker will predispose it to certain tasks, and in some social insects the workers vary in size such that task is associated with worker morphology. In this thesis I explore the proximate and ultimate causes of worker and reproductive division of labour in ant societies, which span a range of social complexities. I predominantly focus on both the highly derived leaf-cutting ants – a so-called ‘pinnacle’ of evolution within the social insects, with a complex division of labour and a strong worker caste system – and in the more basal primitive societies of the queenless ponerine dinosaur ants, which can offer an insight in to the evolution of division of labour at the earliest stages of social lifestyles. This work demonstrates the environmental and genetic determinants of division of labour in group-living societies outside of the classical honey bee model system. This is important as it helps us to better understand the broader processes shaping behaviour and phenotype in the animal kingdom.