Multiple strategies of digenean trematodes to complete their life cycles

This review aims to summarize our most recent knowledge of the unique mechanisms employed by digeneans to complete their complex life cycles. It is based on validated data from scientific literature and integrates both authors’ personal experiences. Several dynamic strategies utilized by digeneans are discussed in relation to their presence in three environments: aquatic, semi-aquatic and terrestrial. The following topics are discussed: transmission from host to host, which involves transmission of free-living stage of miracidium and cercaria: in active transmission – specific responses to environmental signals showing the presence of potential hosts (several papers of Haas et al.); in passive transmission – trophic transmission and mimicry by way of resemblance to natural food of potential host; and finally, transmission of the parasitic larvae (metacercaria and mesocercaria) – trophic transmission, manipulation of host behavior, and incorporating the intermediate host into food web of definitive host. This review also highlights several types of behavioral manipulations, including compensatory processes (Poulin, Lefèvre et al., Thomas et al.), and other mechanisms of manipulation (de Jong-Bring et. al). State-dependent alternative cycles demonstrating the difference between the terms „life cycle” and „life history” (Poulin, Thomas et al.) and the concept of „shared phenotype” (Lefèvre et al.) are also discussed.