Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Dr. Graham Thompson

Abstract

Individuals living within social groups may benefit from the efficiencies of division of labour, but on the other hand render themselves vulnerable to socially transmitted disease. This cost to social living should promote cooperative barriers to disease transmission, especially in eusocial taxa where spatial and genetic proximity to nestmates are characteristically pronounced. Though studies of the immunity at multiple levels in social species are becoming more common, little is known about how their sociality is deployed to resist contagion. By exposing the Eastern subterranean termite Reticulitermes flavipes to entomopathogenic fungi, I studied their immune responses at multiple levels. At the level of group, I found that group size and caste composition affected individual survivorship, and that these effects can be independent of any infection. That is, larger groups or groups of mixed caste simply lived longer. Upon infection, I found that only caste composition, and not group size, affected the group’s ability to survive. This effect from caste, but not from group size, suggests that the group-level immunity in R. flavipes is affected more by the nature rather than the number of social interactions. Within groups, individual termites appeared to express relatively few immune genes, but did so in response to specific fungi and social contexts. R. flavipes expressed specific combinations of immune-genes following exposure to various infective fungal spores. This pathogen-specific expression pattern indicates that R. flavipes maintains a high degree of immunological specificity in its innate immunity, and the degree of the specificity is subject to species-level. Furthermore, some immune genes tended to be less responsive within infected groups, compared to the response of singly infected individuals. But others showed up-regulation on infection regardless of social context. This socially-responsive expression pattern suggests that R. flavipes has the capacity to adjust its innate immune response to its immediate social context. In summary, my behavioral and genetic analyses suggest an adaptive interaction between individual versus collective immunity in a subterranean termite.

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