Travelling with a parasite: the evolution of resistance and dispersal syndrome during experimental range expansion

Spatial dynamics of range-shifting species can be deeply affected by biotic interactions. One ubiquitous type of biotic interaction involves parasites. These can affect nearly all biological systems and impose major selective pressure on the host, leading to rapid evolutionary responses. Despite the potentially large impact of parasites, their role on host dispersal and subsequent range expansions remains mostly unexplored. Therefore, we investigated whether parasites affect and alter host evolution during experimental range expansions. Using microbial model organisms spreading in microcosm landscapes, we found multi-trait evolution and rapid evolutionary shifts in dispersal syndromes due to spatial dynamics and parasitism. As predicted by theory, hosts that had evolved in the absence of parasites changed their movement pattern and increased dispersal at the range margins. The presence of parasites during the range expansion reshaped host phenotypic divergence between front and core, with hosts exhibiting overall reduced dispersal but increased resistance in the front. We suggest that the evolved differences in resistance and other host traits may be associated with a trade-off between dispersal and foraging efficiency. Our work shows that the eco-evolutionary interactions between host and parasite during range expansions can shift the contenders to novel evolutionary trajectories and result in unexpected evolutionary outcomes. Understanding and finding general patterns to these complex dynamics is of critical relevance for conservation and disease management.