Data and Code Repository for: Destabilized host-parasite dynamics in newly founded populations

This study describes the eco-evolutionary dynamics of stickleback and their tapeworm parasites following the experimental introduction of fish into nine lakes. See README text file for details<br>Abstract: When species disperse into previously unoccupied habitats, new populations encounter unfamiliar species interactions such as altered parasite loads. Theory predicts that newly founded populations should exhibit destabilized eco-evolutionary fluctuations in infection rates and immune traits. However, to understand founder effects biologists typically rely on retrospective studies of range expansions, missing early-generation infection dynamics. To remedy this, we experimentally founded whole-lake populations of threespine stickleback. Infection rates were temporally stable in native source lakes. In contrast, newly founded populations exhibit destabilized host-parasite dynamics: high starting infection rates led to increases in a heritable immune trait (peritoneal fibrosis), suppressing infection rates. The resulting temporal auto-correlation between infection and immunity suggest that newly founded populations can exhibit rapid host-parasite eco-evolutionary dynamics.<br>These files have been updated to add 2024 and 2025 data, and to include revised R scripts that have been updated to include new figures, new analyses, and edits in response to reviewer comments.<br>