Biological invasions often include co-invasive parasites that can alter ecosystem function and established native host-parasite relationships. The presence of invasive parasites within the habitat can affect native host fitness and native parasite infection intensity, prevalence, and success within the native host. The mosquito, Aedes triseriatus, is native host to protozoan parasite, Ascogregarina barretti. In areas subject to invasion by the mosquito, Aedes albopictus, this native pairing may also be infected by A. albopictus’ co-invasive parasite, Ascogregarina taiwanensis. We tested the hypotheses that: 1) The presence of a co-invasive parasite will negatively impact native parasite fitness, yielding decreased infection intensity, prevalence, and propagule production, either via immune induction of the host or inter-parasite competition, and 2) Exposure to the co-invasive parasite will negatively impact native host fitness, yielding increased larval development time and decreased survival and reproductive fitness, caused by increased costs of infection. For this investigation, we randomly assigned A. triseriatus larvae to be exposed to controlled doses of the native parasite, the co-invasive parasite, both, or neither. Infection intensity and prevalence were assessed in both the host larvae and adults, and fitness measures were recorded for all hosts.
Results/Conclusions
Exposure to the co-invasive parasite yielded decreased native host survivorship and increased host development time. These effects were not dependent on co-infection with the native parasite and illustrate a potential impact of the co-invasive parasite on host population dynamics. Exposure to the co-invasive parasite reduced native parasite infection intensity in the host larval stage, which indicates both decreased abundance of native parasites successfully infecting the native host and decreased burden in the native host. Native parasite propagule production in adult male, but not female, native hosts was reduced with exposure to the co-invasive parasite. Together, these results indicate the potential for the co-invasive parasite to alter the native host-parasite relationship and to impact native host and native parasite population dynamics.