Infrapopulation dynamics of Halipegus occidualis and Halipegus eccentricus (Digenea: Hemiuridae): temporal changes within individual hosts.

Individual infrapopulations of Halipegus occidualis and Halipegus eccentricus (Hemiuridae) in the buccal cavities of their amphibian host (Rana clamitans) were monitored for changes over time. Rates and patterns of parasite maturation, recruitment, and loss were estimated, and the probabilities of infection for definitive hosts in this system were calculated. Although variable, the time required for maturation of immature worms (once in the buccal cavity) was as little as 1 wk. Relatively rapid losses of worms from individual infrapopulations were observed, although this did not appear to inhibit additional recruitment of these trematodes. Also, it was clear that these species overwintered within their amphibian hosts. There was no statistical difference among the 3 sampling years in the probability of acquiring an initial or a subsequent infection with either parasite. However, we suggest that frogs with an existing infrapopulation may have a greater probability of adding worms if those hosts are within certain foci of infection within the pond. The probability of frogs becoming infected in this system increased in late spring and peaked in midsummer. By examining the temporal changes within individual infrapopulations, it is clear that dynamic changes in infrapopulation size and composition may occur, suggesting that rates of trematode transmission may be greater than previously estimated.