Effects of coinfection with Pomphorhynchus bulbocolli on development of leptorhynchoides thecatus (Acanthocephala) in amphipods (Hyalella azteca).

The effect of the presence of Pomphorhynchus bulbocolli on the development of Leptorhynchoides thecatus (Acanthocephala) in amphipod intermediate hosts (Hyalella azteca) was examined. Two groups of amphipods were exposed either to eggs of both species (experimental) or only to L. thecatus eggs (control). Amphipods of both groups were dissected 39 days postexposure. The percentage of L. thecatus at the cystacanth stage and mean abundance of cystacanths and precystacanths per amphipod were determined. Contingency table analysis and Fisher's exact tests demonstrated that a significantly smaller proportion of L. thecatus reached the cystacanth stage in coinfected amphipods of the experimental group than either worms in the control group or worms in L. thecatus-only infections of the experimental group. Interspecific interaction between acanthocephalans in intermediate hosts has not been reported previously. Coinfection reduces the number of L. thecatus in amphipods available for transmission to definitive hosts. Habitat separation by eggs of L. thecatus and P. bulbocolli might reduce this effect if amphipods are less likely to become coinfected when eggs are in different microhabitats than when they are not.