Phages, or viruses that infect bacteria, are often seen as perfect predators: they hijack their host's cellular machinery to replicate, ultimately killing the host to release new viral progeny. However, certain (temperate) phages can also initiate lysogeny—a latent infection where the viral genome integrates into the host genome, forming a prophage which replicates when the host cell divides. While lysis is an antagonistic host-parasite interaction, lysogeny can be viewed as mutualistic.

Although one might expect lysis to confer higher fitness to the virus due to rapid offspring production, lysogeny remains prevalent across diverse ecosystems, including oceans, soil, and host-associated microbiomes. For instance, conservative estimates suggest that about a fifth of marine bacterial cells harbor prophages. This prevalence highlights the need to understand the ecological drivers of being temperate and the influence of lysogeny on microbial communities.

In this talk, I will first present a theoretical framework for comparing the fitness of lytic and lysogenic viral strategies. I will discuss past work that identifies conditions where lysogeny can outperform lysis in the short-term. Additionally, I will introduce a mathematical framework I developed to explore the eco-evolutionary dynamics of temperate phages over the long-term. In particular, I will demonstrate how periodic environmental changes, such as diurnal or seasonal shifts, can create conflicting selection pressures on different timescales, which ultimately favor intermediate strategies between obligate lysis and obligate lysogeny. Finally, using an environmentally relevant phage-bacteria system, I will show how lysogeny affects microbial communities by enabling multiple phages to coexist with a single host population, in apparent violation of the competitive exclusion principle.