Quality attracts parasites: host condition-dependent chemo-orientation of trematode larvae

1. Environmental factors impairing physiological condition of organisms are assumed to predispose them to parasite infections. This is because host immune function is typically condition-dependent. However, poor physiological condition has been reported to reduce host susceptibility to parasites in various systems. 2. We examined whether such an effect can be due to altered exposure of hosts to active parasite transmission stages by investigating chemo-orientation of free-swimming cercariae larvae of a parasite Echinoparyphium aconiatum towards its snail host Lymnaea stagnalis. 3. We used both long-term and short-term feeding treatments to manipulate the body condition and physiological traits related to food processing in experimental (i.e. target) snails and measured the preference of cercariae towards snail-conditioned water (SCW) over clean water. 4. We found that chemo-orientation of cercariae depended on the nutritional status of target snails. High physiological condition (long-t...