Dauer life stage of Caenorhabditis elegans induces elevated levels of defense against the parasite Serratia marcescens.

Host-parasite research often focuses on a single host life stage, yet different life stages may exhibit different defenses. The nematode Caenorhabditis elegans has an alternate dispersal life stage, dauer. Despite dauer's importance in nature, we know little of how it responds to parasites. Previous research indicates that non-dauer C. elegans prefer to consume the virulent bacterial parasite, Serratia marcescens, when given a choice between the parasite and benign Escherichia coli. Here, we compared the preferences of dauer individuals from six strains of C. elegans to the preferences of other life stages. We found that dauer individuals exhibited reduced preference for S. marcescens, and dauers from some strains preferred E. coli to S. marcescens. In addition to testing food preference, a mechanism of parasite avoidance, we also measured host mortality rates after direct parasite exposure to determine if life stage also altered host survival. Overall, dauer individuals exhibited reduced mortality rates. However, dauer versus non-dauer larvae mortality rates also varied significantly by host strain. Collectively, we found evidence of dauer-induced parasite avoidance and reduced mortality in the presence of a parasite, but these effects were strain-specific. These results demonstrate the importance of host life stage and genotype when assessing infection dynamics.