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Free keywords:
conflict; cooperation; parasite-parasite interactions; cestode; copepod;
experimental infections
Abstract:
Host manipulation is a common parasite strategy to alter host behavior in a manner to
enhance parasite fitness usually by increasing the parasite’s transmission to the next host. In
nature, hosts often harbour multiple parasites with agreeing or conflicting interests over host
manipulation. Natural selection might drive such parasites to cooperation, compromise or
sabotage. Sabotage would occur, if one parasite suppresses the manipulation of another.
Experimental studies on the effect of multi-parasite interactions on host manipulation are
scarce, clear experimental evidence for sabotage is elusive. We tested the effect of multiple
infections on host manipulation using lab bred copepods experimentally infected with the
trophically transmitted tapeworm Schistocephalus solidus. This parasite is known to
manipulate its host depending on its own developmental stage. Coinfecting parasites with the
same aim enhanced each other’s manipulation but only after reaching infectivity. If the
coinfecting parasites disagree over host manipulation, the infective parasite wins this conflict:
the non-infective one has no effect. The winning (i.e. infective) parasite suppresses the
manipulation of its non-infective competitor. This presents conclusive experimental evidence
for both cooperation in and sabotage of host manipulation and hence a proof of principal that
one parasite can alter and even neutralize manipulation by another.
