Host traits measurements after evolution with or without parasites during range expansions

Rapid evolutionary changes during range expansions can lead to the divergence between range core and front populations, with the emergence of dispersal syndromes. Besides intraspecific effects, range expansions may be impacted by interspecific interactions such as parasitism. Yet, despite the potentially large impact of parasites imposing additional selective pressures on the host, their role on range expansions remains largely unexplored. Here, we investigated whether parasites affect the evolution of host dispersal syndromes during spatial spread. Using populations of the ciliate Paramecium caudatum and its bacterial parasite Holospora undulata spreading in microcosm landscapes, we studied experimental range expansions under the presence or absence of the parasite. We found that range expansion and parasite treatments acted independently on the evolution of host dispersal syndromes. Front host populations showed different trait associations between swimming behaviour and population gr...