Seasonal exchange of microsporidian parasites between native and non-native pet-traded freshwater crustaceans: Is parasite spillover favored over spillback?

The introduction of non-native pet-traded species poses potential threats to global biodiversity, particularly in freshwater ecosystems. This study investigated the seasonal dynamics of microsporidian infections in an established feral population of cherry shrimp (Neocaridina davidi) and the coexisting populations of crustaceans, comprising both native and non-native species, inhabiting the thermal waters of the Fontcaude Park and the nearby Mosson River in southern France. Our aim was to assess the potential occurrence of spillover and/or spillback events between N. davidi and co-occurring crustaceans, as well as the influence of seasonal dynamics on these interactions. The prevalence and diversity of microsporidian parasites exhibited strong seasonal variations. Although parasites associated with the pet trade were not detected, we highlight the acquisition of native parasites by feral N. davidi, which seems to be a suitable alternative host for native host-generalist microsporidians. Our findings indicate that all prerogatives for spillback events to occur are met. Feral N. davidi may establish and survive year-round in European rivers with natural thermal regimes. Thus, human-mediated introductions can potentially alter parasite transmission dynamics in these ecosystems.