Macquarie University
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The evolution of sociality and antimicrobial defences in wasps

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posted on 2022-03-28, 12:01 authored by Stephen James Hoggard
Cuticular antimicrobial compounds are a front-line defence against disease that restrict the growth and transmission of pathogens within groups of social insects. I explore the hypothesis that these compounds were integral to both the evolution of early social aggregations and the development of more complex social systems. The strength of cuticular antimicrobials was assayed from wasp species representing a range of group sizes and life history traits. Wasps were chosen because they are a basal group within social Hymenoptera and present species with a range of social structures. Across species, nesting substrate type and levels of social complexity were strongly correlated with the strength of antimicrobial compounds. Phylogenetic analysis suggested that these compounds arose first in solitary, ground-dwelling species. Across colonies of a social species, traits varied with respect to how they influenced the strength of antimicrobial defences; group size and genetic diversity had strong but opposing correlations with antimicrobial strength. Conversely, microbial load was low across colonies and did not appear to vary with antimicrobial strength. These data suggest antimicrobial defences in wasps first evolved as a defence against soil-borne pathogens. As group sizes increased the pressure of disease risk selected for increasingly strong antimicrobial compounds. Low microbial associations indicate that these compounds are highly effective in social species however correlations with group size and genetic diversity suggest that disease risk remains a major selective pressure on maximum attainable group sizes. I propose a model of the relationship between group size, genetic diversity and the risk of disease that may be used to predict the largest stable group sizes. These findings illuminate both the historical and contemporary selective pressure that disease risk has placed on cuticular antimicrobial compounds. Further, these data provide unique insights and research avenues for both bio-prospecting and social insects in general.


Table of Contents

Disease risk and the evolution of social insects -- Methodology -- Social complexity and nesting habits are factors in the evolution of antimicrobial defences in wasps -- The effectiveness of cuticular antimicrobials in a social wasp declines with group size and genetic similarity -- Microbial load in a social insect and the implications for the role of antimicrobial defences -- Conclusions -- Appendix A: Antimicrobial strength increases with group size: implications for social evolution -- Appendix B: Mating system and genetic structure in the paper wasp (Polistes humilis) -- Appendix C: R script for Gompertz curve calculations -- Appendix D: Biosafety approval.


Includes bibliographical references Thesis by publication.

Awarding Institution

Macquarie University

Degree Type

Thesis PhD


Thesis (PhD), Macquarie University, Faculty of Science, Department of Biological Sciences

Department, Centre or School

Department of Biological Sciences

Year of Award


Principal Supervisor

Adam Stow

Additional Supervisor 1

Michael Gillings

Additional Supervisor 2

Andrew Beattie


Copyright disclaimer: Copyright Stephen James Hoggard 2012.




1 online resource (xii, 162 p.)

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