Egg dispersal in the acanthocephalan Acanthocephalus dirus: field data.

Among acanthocephalans, eggs are typically dispersed in the feces of definitive hosts. A recent laboratory-based study provided support for the hypothesis that some female acanthocephalans (Acanthocephalus dirus) carry eggs into the environment prior to dispersal. Here, we examined the potential occurrence of this relationship under natural conditions. Using 6 field surveys, we searched the sediment of a local stream to determine whether the bodies of A. dirus females could be located. We recovered the bodies of 24 intact A. dirus individuals from the stream sediment, of which 5 were mature females. All 5 of the mature females contained mature eggs, with 1 female carrying approximately 10,000. These results are consistent with the interpretation that eggs can be dispersed from the bodies of female A. dirus in nature. We also found that there was significant variation in the number of mature eggs present in the females, with 4 of the 5 females carrying fewer than 400 mature eggs. In addition, we recovered approximately 20,000 mature eggs from a fecal pellet that had been expelled from a fish. We propose that eggs may be dispersed both in the feces of definitive hosts and from the bodies of expelled female A. dirus under natural conditions.