Social organisation and pathogen transmission in African ants: at what point do social immunity benefits diminish?

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dc.contributor.advisorWossler, Theresaen_ZA
dc.contributor.advisorHui, Cangen_ZA
dc.contributor.authorPhair, Daviden_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Botany and Zoology.en_ZA
dc.date.accessioned2020-02-21T13:28:40Z
dc.date.accessioned2020-04-28T15:14:19Z
dc.date.available2020-02-21T13:28:40Z
dc.date.available2020-04-28T15:14:19Z
dc.date.issued2020-04
dc.descriptionThesis (PhD)--Stellenbosch University, 2020.en_ZA
dc.description.abstractENGLISH ABSTRACT: Eusocial insects, and ants in particular, encounter a range of pathogens, often generalist entomopathogenic fungi that profit from their hosts’ dense living conditions and high relatedness. Ants exploit a range of individual behaviours that ameliorate pathogen impacts on the colony, collectively termed “social immunity”. Species with different life histories and ecologies combat fungal infections using different approaches. This study assessed a range of social immunity mechanisms employed by three South African ant species, Anoplolepis custodiens, Camponotus fulvopilosus and Tetramorium sericeiventre. Self-grooming, allogrooming, trophallaxis, and organisational immunity, as well as the effect of group size, were assessed through a range of methods including group level observations, colony level observations, spatial use assessments, interaction networks, and mathematical models. In assessments of group level effects, I showed that as group size increases ants increased their investment in grooming to remove conidia. Further, I showed that all three species responded to pathogen exposure by increasing interaction rates and mitigated exposure to the generalist entomopathogenic fungus, Metarhizium anisopliae. Mortality did not differ 21 days post- exposure compared to control treated ants, with access to nestmates and social immune interactions. Each species drastically lowered the number of conidia on their cuticle if allowed to groom; however, C. fulvopilosus displayed ineffective allogrooming. Commonly, ants increased the frequency and decreased the duration of allogrooming in response to exposure. Species displayed differential response in these behaviours with A. custodiens grooming most frequently and C. fulvopilosus allogrooming the least. The duration and frequency of trophallaxis was maintained in response to exposure, with A. custodiens engaging in the most trophallaxis, in terms of both frequency and duration. Assessing organisational immunity in the form of spatial use patterns, I showed that all three species displayed clustering within nests, likely limiting pathogen transmission. Only A. custodiens, however, showed spatial separation between foragers and the queen and further increased clustering in response to exposure, limiting pathogen spread. I generated interaction networks for C. fulvopilosus obtaining data from behavioural recordings of experimental colonies and calculated network metrics before and after pathogen exposure. Camponotus. fulvopilosus decreased network connectivity in response to pathogen exposure which limits pathways for pathogen spread. Finally, I generated matrix projection models based on the data to assess how each of the three species managed exposure to fungi, by tracking spores as they are managed by self-grooming and allogrooming. All three species were able to mitigate pathogen exposure, removing all conidia before they could lead to infection. Anoplolepis custodiens relied primarily on allogrooming whilst C. fulvopilosus relied only on self-grooming to remove conidia. Tetramorium sericeiventre relied primarily on self-grooming but also benefitted from allogrooming. Overall, I show that three African ant species mitigate exposure to a generalist entomopathogenic fungus through a different combination of behavioural social immunity mechanisms, highlighting the importance of assessing several pathogen control mechanisms across multiple species. This represents the first assessment of social immunity in South Africa, showing that three species use either individual or collective behaviours to mitigate fungal exposure.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Geen opsomming beskikbaaraf_ZA
dc.description.versionDoctoralen_ZA
dc.format.extent173 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/108447
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectSocial immunityen_ZA
dc.subjectAnt communities -- Behavioren_ZA
dc.subjectInsect societiesen_ZA
dc.subjectEntomopathogenic fungien_ZA
dc.subjectAnts -- Ecologyen_ZA
dc.subjectUCTDen_ZA
dc.subjectUCTDen_ZA
dc.titleSocial organisation and pathogen transmission in African ants: at what point do social immunity benefits diminish?en_ZA
dc.typeThesisen_ZA
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Doctoral Degrees (Botany and Zoology)