Disease defence in garden ants

C. Pull, Disease Defence in Garden Ants, IST Austria, 2017.

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Thesis | Published | English
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IST Austria Thesis
Contagious diseases must transmit from infectious to susceptible hosts in order to reproduce. Whilst vectored pathogens can rely on intermediaries to find new hosts for them, many infectious pathogens require close contact or direct interaction between hosts for transmission. Hence, this means that conspecifics are often the main source of infection for most animals and so, in theory, animals should avoid conspecifics to reduce their risk of infection. Of course, in reality animals must interact with one another, as a bare minimum, to mate. However, being social provides many additional benefits and group living has become a taxonomically diverse and widespread trait. How then do social animals overcome the issue of increased disease? Over the last few decades, the social insects (ants, termites and some bees and wasps) have become a model system for studying disease in social animals. On paper, a social insect colony should be particularly susceptible to disease, given that they often contain thousands of potential hosts that are closely related and frequently interact, as well as exhibiting stable environmental conditions that encourage microbial growth. Yet, disease outbreaks appear to be rare and attempts to eradicate pest species using pathogens have failed time and again. Evolutionary biologists investigating this observation have discovered that the reduced disease susceptibility in social insects is, in part, due to collectively performed disease defences of the workers. These defences act like a “social immune system” for the colony, resulting in a per capita decrease in disease, termed social immunity. Our understanding of social immunity, and its importance in relation to the immunological defences of each insect, continues to grow, but there remain many open questions. In this thesis I have studied disease defence in garden ants. In the first data chapter, I use the invasive garden ant, Lasius neglectus, to investigate how colonies mitigate lethal infections and prevent them from spreading systemically. I find that ants have evolved ‘destructive disinfection’ – a behaviour that uses endogenously produced acidic poison to kill diseased brood and to prevent the pathogen from replicating. In the second experimental chapter, I continue to study the use of poison in invasive garden ant colonies, finding that it is sprayed prophylactically within the nest. However, this spraying has negative effects on developing pupae when they have had their cocoons artificially removed. Hence, I suggest that acidic nest sanitation may be maintaining larval cocoon spinning in this species. In the next experimental chapter, I investigated how colony founding black garden ant queens (Lasius niger) prevent disease when a co-foundress dies. I show that ant queens prophylactically perform undertaking behaviours, similar to those performed by the workers in mature nests. When a co-foundress was infected, these undertaking behaviours improved the survival of the healthy queen. In the final data chapter, I explored how immunocompetence (measured as antifungal activity) changes as incipient black garden ant colonies grow and mature, from the solitary queen phase to colonies with several hundred workers. Queen and worker antifungal activity varied throughout this time period, but despite social immunity, did not decrease as colonies matured. In addition to the above data chapters, this thesis includes two co-authored reviews. In the first, we examine the state of the art in the field of social immunity and how it might develop in the future. In the second, we identify several challenges and open questions in the study of disease defence in animals. We highlight how social insects offer a unique model to tackle some of these problems, as disease defence can be studied from the cell to the society.
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ERC FP7 programme (grant agreement no. 240371) I have been supremely spoilt to work in a lab with such good resources and I must thank the wonderful Cremer group technicians, Anna, Barbara, Eva and Florian, for all of their help and keeping the lab up and running. You guys will probably be the most missed once I realise just how much work you have been saving me! For the same reason, I must say a big Dzi ę kuj ę Ci to Wonder Woman Wanda, for her tireless efforts feeding my colonies and cranking out thousands of petri dishes and sugar tubes. Again, you will be sorely missed now that I will have to take this task on myself. Of course, I will be eternally indebted to Prof. Sylvia Cremer for taking me under her wing and being a constant source of guidance and inspiration. You have given me the perfect balance of independence and supervision. I cannot thank you enough for creating such a great working environment and allowing me the freedom to follow my own research questions. I have had so many exceptional opportunities – attending and presenting at conferences all over the world, inviting me to write the ARE with you, going to workshops in Panama and Switzerland, and even organising our own PhD course – that I often think I must have had the best PhD in the world. You have taught me so much and made me a scientist. I sincerely hope we get the chance to work together again in the future. Thank you for everything. I must also thank my PhD Committee, Daria Siekhaus and Jacobus “Koos” Boomsma, for being very supportive throughout the duration of my PhD.

Cite this

Pull C. Disease Defence in Garden Ants. IST Austria; 2017. doi:10.15479/AT:ISTA:th_861
Pull, C. (2017). Disease defence in garden ants. IST Austria. https://doi.org/10.15479/AT:ISTA:th_861
Pull, Christopher. Disease Defence in Garden Ants. IST Austria, 2017. https://doi.org/10.15479/AT:ISTA:th_861.
C. Pull, Disease defence in garden ants. IST Austria, 2017.
Pull C. 2017. Disease defence in garden ants, IST Austria, 122p.
Pull, Christopher. Disease Defence in Garden Ants. IST Austria, 2017, doi:10.15479/AT:ISTA:th_861.
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