Coinvasion biology of endoparasites and highly clonal hosts

The ability to disperse and become established elsewhere is crucial for organisms as environmental quality varies over space and time. Many parasites produce resistant stages that can achieve dispersal independently from hosts. However, co-dispersal of parasites with hosts offers another means of dispersal. Here we focus on how dispersal and establishment of endoparasites with complex life cycles may promote invasion of freshwater environments. We review factors that could contribute to such invasion, present evidence for dispersal and invasions of malacosporean myxozoans, and consider how co-dispersal with their invertebrate hosts (freshwater bryozoans) may drive these processes. We develop this bryozoan/myxozoan association as a model system for assessing probability and risks of endoparasite invasion. Recurrent clonal reproduction in bryozoan hosts in concert with myxozoan traits (broad host ranges, host-condition dependent development) are proposed to particularly promote invasion. It is difficult to predict how global change may influence invasion and diseases caused by myxozoans in vertebrate hosts (fish) due to conflicting impacts and lack of knowledge. These include impacts of eutrophication and warming waters versus declines in migratory birds, poor knowledge of host ranges in parasites with complex life cycles, and recognition of hidden infections.