R. Knudsen et al., Selective predation on parasitized prey - A comparison between two helminth species with different life-history strategies, J PARASITOL, 87(5), 2001, pp. 941-945
In Lake Fjellfrosvatn, northern Norway, the larval helminths Cyathocephalus
truncatus and Cystidicola farionis use Gammarus lacustris as intermediate
hosts and Arctic chaff (Salvelinus alpinus) as final hosts. There was sampl
ed 1,433 live G. lacustris from the lake and 1,964 G. lacustris from stomac
h contents of the cham Prevalence of infection were, respectively, 0.49 % a
nd 3.72% for C. truncatus, and 0.2 1 % and 0.20% for C. farionis. Usually,
only I parasite was present in each host, and the 2 parasite species never
co-occurred. Gammarus lacustris amphipods parasitized by C. truncatus were
positively selected by the Arctic charr and were consumed approximately 8 t
imes as often as were the unparasitized amphipods or the amphipods infected
with C. farionis. This suggests that G. lacustris amphipods infected with
C. truncatus larvae are more susceptible to predation than noninfected spec
imens, probably because of parasite-induced alterations in behavior or visi
bility. Alternatively, this could also be explained by selection toward the
largest G. lacustris specimens observed, which are also the most frequentl
y parasitized amphipods. However, the data show clearly that this was not a
result of size-selective predation by the charr. In contrast, the presence
of C. farionis did not increase the susceptibility to predation of its int
ermediate host. The discrepancy between the 2 helminth species supports the
hypothesis that parasite-increased susceptibility to predation is related
to the life history strategies of the parasites.