Goodnight, Sarah R.

Complex life cycles are common across parasite taxa and frequently require trophic transfer of parasites from prey to predator; however, studies on parasite-host interactions often neglect variation in parasite life histories. Here I use two focal freshwater digenetic trematode species, Halipegus occidualis tongueworms and Haematoloechus complexus lungworms, as an empirical system to investigate how parasite life history traits drive host-parasite interactions across the life cycle. To examine how parasite life history and host ecology influence parasite genetic patterns, I characterized the genetic diversity of within-host infrapopulations, as well as overall population genetic structure, of sympatric tongueworm and lungworm populations. Infection load and genetic diversity of host-level parasite infrapopulations increased with host trophic level, highlighting the benefits of trophic transfer and multihost life cycles. Concurrently, first intermediate host population dynamics and dispersal ability played a role in predicting population-level parasite genetic diversity and structure.