PS 11-162 - Contracaecum multipapillatum prevalence and intensity of infection in the introduced brook stickleback as a case study of biotic resistance

Abstract: The enemy release hypothesis suggests that the success of invasive species in the initial phases of invasions is partially due to escape from predators and pathogens in their native range. However, according to the biotic resistance hypothesis, the immediate success of non-native species is time-dependent due to native predators and pathogens’ ability to shift prey and hosts to make use of new introductions. Introduced species function as either direct predators or highly efficient resource competitors to their native counterparts. It is therefore important to understand potential limiting factors of such individual’s success and how it relates to largescale ecosystem impacts. The brook stickleback is a newly introduced species in eastern Washington that has high population densities. These fish are parasitized by Contracaecum multipapillatum, a nematode in the Anisakidae family that has a complex life cycle targeting a range of species including fish, piscivorous birds, and mammals. The goals of this study are to calculate both the prevalence and intensity of infection of C. multipapillatum as measured by the average number of nematodes found in brook stickleback. We collected brook stickleback at Middle Pine Lake within Turnbull National Wildlife Refuge in October of 2017, 2019, and 2022. Necroscopy of fish was performed to identify presence or absence of the nematode and the number of nematodes per individual host was recorded. We found that the prevalence of infection of C. multipapillatum in brook stickleback was significantly higher at 40% in 2019 versus 15% at both 2017 and 2022. Intensity of infection was not different between years. This analysis demonstrates interannual variability in the prevalence of C. multipapillatum infection in introduced brook stickleback. Investigation into dynamics of this system provides insight into interspecific relationships and naturally occurring biotic resistance, providing a potential case study for this hypothesis.