INVERTEBRATE IMMUNE PRIMING: AN INTEGRATION OF MECHANISM, LIFE HISTORY, AND DISEASE DYNAMICS

Abstract

Invertebrate animals lack the mechanistic machinery of the vertebrate adaptive immune system, but they are still capable of generating extra protection, called primed immunity, against pathogens they have been exposed to before. This protection can even be passed trans-generationally from mothers to offspring, and manifests as an increased probability of survival following secondary infection. Invertebrate immune priming has ignited substantial interest in the biological community in recent years because it challenges core notions about the disparate nature of innate and adaptive immunity and, in some sense, our preconceptions about the uniqueness and superiority of mammals. However, very little is known about the underlying physiological mechanisms of immune priming or how immune priming ultimately impacts insect population dynamics and host-pathogen interactions.

In this dissertation, I combine mathematical models and experimental approaches to investigate potential mechanisms, life history trade-offs, and population level patterns associated with immune priming in flour beetles (Tribolium castaneum) against the bacterial entomopathogen Bacillus thuringiensis. My results suggest that the primed phenotype arises from a combination of resistance and tolerance mechanisms that result in a reduced disease-induced mortality rate for trans-generationally primed larvae. This protection co-occurs with an increase in the developmental rate of primed offspring, a relationship that may arise from extensive shared genetic architecture between development and immunity. This life history shift is conserved in both laboratory and wild beetle populations, and can be inhibited by co-infection with other parasites. Insects, both as carriers and victims of infection, play a vital role in human health, food security, and agriculture across the globe, and this body of work underscores the important role that immune priming might play in modulating these crucial processes.