An examination of the manipulation hypothesis to explain prevalence of Parelaphostrongylus tenuis in gastropod intermediate host populations.

摘要

The prevalence of Parelaphostrongylus tenuis, a nematode parasite of white-tailed deer (Odocoileus virginianus) in eastern North America in deer populations is typically high compared with its prevalence in its gastropod intermediate hosts. It is unclear how high levels of prevalence are maintained, given that the transmission of this parasite to deer is considered to occur by the accidental ingestion of infected gastropods. This study investigated whether this pattern might be caused by behavioural manipulation of the snails by the parasites to increase transmission. The vertical climbing behaviour of infected and uninfected individuals of a known intermediate host species, Mesodon sayanus, was compared. Snails climbed higher at dawn than duringthe rest of the day and adults climbed higher than juveniles, but no differences were found between infected and uninfected snails. These results do not explain the observed levels of prevalence, but they improve understanding of the transmission of P. tenuis, particularly with regard to the relative importance of different gastropod intermediate hosts. Competing hypotheses that might account for the apparent discrepancy in levels of prevalence are briefly reviewed.