Introduced brown trout alter native acanthocephalan infections in native fish

Area of Science:

• Ecology
• Parasitology
• Invasive Species Biology

Background:

• Introduced species can alter native host-parasite dynamics by acting as parasite reservoirs or sinks.
• Negative correlations between brown trout and native parasite burdens in roundhead galaxias suggest parasite dilution in New Zealand.

Purpose of the Study:

• To investigate if native Acanthocephalus galaxii acquisition by introduced brown trout alters host-parasite dynamics in native roundhead galaxias.
• To determine the role of brown trout in the transmission dynamics of Acanthocephalus galaxii.

Main Methods:

• A multi-scale approach combining field observations, experimental infections, and dynamic population modeling.
• Assessing parasite intensity and maturity in both native galaxias and introduced brown trout.
• Modeling parasite dynamics in relation to host densities and predation rates.

Main Results:

• Field observations and experimental infections indicated that Acanthocephalus galaxii does not mature in brown trout, supporting the parasite sink hypothesis.
• Trout exhibited higher infection intensity but only immature parasites, while galaxias had lower intensity with mature parasites.
• Dynamic population modeling predicted only slight reductions in galaxias parasite burdens due to dilution by trout.

Conclusions:

• Brown trout may act as an infection sink for Acanthocephalus galaxii, but the overall impact on native galaxias parasite burdens is limited.
• Parasite densities in galaxias are highly sensitive to galaxias predation on infected amphipods and relative host abundances.
• Trout may reduce galaxias parasite burdens indirectly by altering galaxias density or foraging behavior, rather than solely through parasite dilution.