The Alteration of Life History Traits and Increased Success of Halipegus eccentricus Through the Use of a Paratenic Host: A Comparative Study.

Complex life cycles are a hallmark characteristic of many parasites; however, little is known about the process by which life cycles become more complex through the addition of hosts. Paratenic hosts are present in the life cycles of several phylogenetically distinct groups of helminths; this suggests that they may play a key role during this process. This study examined the development of metacercariae of Halipegus eccentricus within intermediate microcrustacean and odonate paratenic hosts. Then a comparative approach was used to evaluate how life history traits of H. eccentricus within the anuran definitive hosts differ between metacercariae of the same age that developed within an intermediate ostracod host or a paratenic odonate host. The results of this study indicate that metacercariae of H. eccentricus do not grow at the same rate in different intermediate hosts, and significant differences exist in growth within intermediate and paratenic hosts. Individuals from odonate paratenic hosts always had larger bodies and suckers than those of metacercariae of the same age that develop within microcrustacean intermediate hosts. Furthermore, metacercariae from odonates were more successful in establishing and migrating in definitive anuran hosts. Last, individuals from paratenic hosts began reproducing earlier within anuran definitive hosts than age-matched worms that develop within the intermediate hosts. Collectively these results suggest that the variation in body and sucker sizes within odonate and microcrustacean hosts may carry over to the definitive host and in the case of H. eccentricus using the paratenic host increases transmission and alters other life history traits within definitive hosts. These results indicate that using a paratenic host can affect the success of parasites in subsequent hosts, and therefore these hosts may provide benefits other than just increasing transmission by bridging an ecological gap.