Data from: 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-term feeding) attracted parasites, but cercariae did not show preference towards SCW from individuals in poor physiological condition (long-term starvation). Food processing (short-term feeding treatments) did not affect chemo-orientation. 5. Our results suggest that host condition-dependent chemo-orientation of parasite larvae is a likely mechanism explaining the reduced susceptibility of snails to infection due to food limitation in our study system. In general, the use of condition-dependent host cues can be highly beneficial for parasites as it increases their transmission to high-quality hosts. Furthermore, evolving counter adaptations to such a transmission strategy can be very difficult for hosts