Abstract
Introduced species can modify local host-parasite dynamics by amplifying parasite infection which can 'spill-back' to the native fauna, whether they are competent hosts for local parasites, or by acting as parasite sinks with 'dilution' of infection decreasing the parasite burden of native hosts. Recently infection by the trematode Bucephalus polymorphus has increased in several European rivers, being attributed to the introduction of intermediate host species from the Ponto-Caspian region.
Using a combination of field and experimental data, we evaluated the competence of non-native and native fish as intermediate hosts for B. polymorphus and its role for parasite development in a definitive host. We detected high natural infection parameters of B. polymorphus in native cyprinids and non-native gobies compared to data from the period prior to goby establishment.
Both fish groups are consumed by predatory fish and represent a major component of the littoral fish community. Parasite establishment and adult size in definitive hosts was equivalent among the second intermediate host species, despite a lower size of metacercariae recovered from round gobies.
However, development in the definitive host of flukes recovered from gobies was reduced, showing higher mortality, delayed maturity and lower egg production, in comparison with parasites from native hosts. Conclusions: Substantial 'spill-back' of B. polymorphus due to higher transmission rates after establishment of non-native gobies was partially buffered by decreased fitness of B. polymorphus that underwent development in gobies.