Detrimental effects of a failed infection by a co-invasive parasite on a native congeneric parasite and its native host.

Biological invaders often are accompanied by co-invasive parasites that can alter ecosystem function and established native host-parasite relationships. When these co-invasive parasites establish in a community, they can affect native host fitness and native parasite infection intensity, prevalence, and success within the native host. The mosquito, , is North American host to protozoan parasite, . In geographic regions invaded by the mosquito , may also be infected by co-invasive parasite, . We tested the hypotheses that: 1) The presence of a co-invasive parasite will negatively affect native parasite fitness, yielding decreased infection intensity, prevalence, and infection success, which could be caused by immune induction of the host or inter-parasite competition, and 2) Coinfection with the native and co-invasive parasites will negatively affect host fitness, yielding increased larval development time and decreased survival and reproductive fitness, caused by increased costs of infection. In our coinfection experiments we find that any exposure to the co-invasive parasite resulted in decreased survivorship and increased development time of the host , with or without coinfection by the native parasite. Exposure to both co-invasive and native parasites yielded reduced native parasite infection intensity in the host larva and reduced native parasite propagule production in the resulting male adults. Together, these results indicate not only the potential for the co-invasive parasite to alter the native host-parasite relationship, but to impact native host population dynamics.