Population and infection dynamics of Daubaylia potomaca (Nematoda: Rhabditida) in Helisoma anceps

Daubaylia potomaca is an unusual parasite for several reasons. Specifically, it has a direct life cycle in which it uses a planorbid snail, Helisoma anceps , as the definitive host. In addition, adult females have been shown to be both the infective stage and the only stage documented to be shed from a live, infected host. Finally, adults, juveniles, and eggs have been observed in all tissues and blood spaces of the host, suggesting the parasite consumes and actively migrates through host tissue. The present study examined the population and infection dynamics of D. potomaca in Mallard Lake, a 4.9-ha public access pond in the Piedmont region of North Carolina. In particular, the study examined the role of seasonality on the prevalence and mean intensity of infection of D. potomaca in the snail host. Data collected from August 2008 to October 2009 suggest that prevalence and mean intensity were inversely related in the spring and fall. Prevalence in fall 2008 was 10.3% but increased to 47.3% in spring 2009. Conversely, intensity was high in fall 2008 at 52.4 ± 8.9 worms/infected host but dropped to 3.1 ± 0.3 worms/infected host in spring 2009. During the same time, the parasites within the snails went from highly aggregated populations in the fall to a less aggregated distribution in the spring. It is hypothesized that D. potomaca induces mortality of the snail hosts during the winter, followed by a rapid recruitment event of the nematodes by the snail population after torpor.