Invading the Occupied Niche: How a Parasitic Copepod of Introduced Oysters Can Expel a Congener From Native Mussels

In species introductions, non-native are often confronted with new niches occupied by more specialized natives, and for introduced parasites this conflict can be amplified because they also face novel hosts. Despite these obstacles, invasions of occur frequently, but the mechanisms that facilitate parasite invasion success only rarely explored. Here, we investigated how parasitic copepod Mytilicola orientalis , recently spilled over from its principal host - Pacific oyster Crassostrea gigas managed to invade niche blue mussel Mytilus edulis intestines, which is densely specialist congener, intestinalis . From field observations demonstrating dynamics in nature, designed a series experiments addressing potential facilitating successful occupation niche. As expected M. infect hosts, displayed higher infection there than both combined. absence direct competitive interactions compensated lower (1) recurrent spill-over high-fitness reservoir host, (2) active aggregation interference enhancing own mating while limiting intestinalis. The could thus avoid competition changing epidemiology indirectly decreasing reproductive competitor host. Such outside have seldom been considered, crucial understand success, range community assembly context introductions.