Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Applied Mathematics

Supervisor

Wild, Geoff

Abstract

Pathogens can be transmitted both vertically (from the parent to the offspring) and horizontally. Here, I model the co-evolution of pathogens and their hosts allowing for vertical and horizontal transmission and density-dependent host population growth. My analysis uses evolutionary game theory. I use computational methods to find that increasing vertical transmission does not always result in more benign disease outcomes. Instead, it can lead to higher pathogen-induced mortality. Furthermore, more benign outcomes evolve more readily when horizontal transmission is more profitable for the pathogen, and overall virulence increases as horizontal transmission becomes more profitable. The results also indicate that vertical transmission, when associated with high virulence, can drive selection-driven extinction of the pathogen, which highlights the importance of considering both transmission modes in evolutionary studies.

Summary for Lay Audience

My research focuses on the co-evolution of pathogens (agents causing disease) and their hosts (the organisms they infect), exploring how diseases spread and evolve. There are two main ways pathogens can transmit: from parent to offspring (vertical transmission) and between individuals in the same generation (horizontal transmission). Understanding these patterns helps us learn how diseases affect their hosts over time.

Using mathematical models and computer simulations, I study these interactions to predict changes. Surprisingly, increasing transmission from parent to offspring does not always make the disease less harmful. In fact, it can sometimes make it deadlier.

I also found that the severity of a disease can increase if spreading between individuals becomes more advantageous for the pathogen. Interestingly, highly deadly diseases that rely on both vertical and horizontal transmission can sometimes drive themselves to extinction by killing their hosts too quickly.

These findings help us understand the complex co-evolutionary relationships between hosts and pathogens, showing that the way diseases spread greatly influences their overall impact.

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