Microsporidia are coming: Cucumispora ornata and Dictyocoela berillonum invade Northern Britain

Biological invasions are a driving force for biodiversity decline, worldwide. These dynamic systems often include the transference of symbiotic or pathogenic organisms that display their own threat to local fauna. Alternatively, parasites introduced during an invasion can help to control the invasive host population and limit ecological damage. To understand invasion systems that include parasites, it is important to record the presence of invasive parasites as they travel to novel locations. In this study, we screen non-native Dikerogammarus haemobaphes located in Boroughbridge (United Kingdom) for microsporidian parasites, using a PCR diagnostic. We found a prevalence of 9.1% for two microsporidian pathogens: Cucumispora ornata and Dictyocoela berillonum. Genetic data for the two parasites and accompanying haplotype maps are used to determine potential origin and relatedness. Our hapmap for C. ornata indicates two haplotypes of this parasite in the UK, sharing similarities with isolates from Poland and Germany. For D. berillonum, our data concur with recent findings that this parasite does not appear to have high relative genetic variability and shares similarities with isolates across the EU and from multiple hosts. These microsporidian pathogens have a wide host range and pose a risk to surrounding native crustacean fauna. We report the presence of these two parasites in their most northern range and consider their likely origin and connectivity with other isolates across the UK, Europe, and Russia.