What doesn’t kill you doesn’t make you stronger: Parasites modify interference competition between two invasive amphipods

We used a freshwater amphipod-microsporidian model (Ponto-Caspian hosts: Dikerogammarus villosus and D. haemobaphes , parasite: Cucumispora dikerogammari ) to check whether parasites affect biological invasions by modulating behaviour intra- interspecific interactions between the invaders. tested competition for shelter in conspecific heterospecific male pairs (one or both individuals infected non-infected). In general, amphipods of species increased their occupancy time when accompanied rather than non-infected conspecifics heterospecifics. Infected faced lower aggression from conspecifics. Moreover, was more aggressive towards vs. summary, infection reduced competitivity amphipods, which became less capable defending shelters, despite unchanged need occupancy. commonly considered as weaker competitor, displaced co-occupied locations, able compete efficiently with microsporidian infections appeared on scene. This suggests that may be important mediators invasions, facilitating existence large assemblages invasive alien amphipods.