Experimental evidence of parasite-induced alteration of host behavior in a complex parasite-host system

The complex interactions between parasites and their hosts are poorly understood. Parasite-induced behavioral alterations in the intermediate host can, in certain cases, make a host more susceptible to predation, thereby facilitating the transmission of the parasites to their definitive hosts. In this study, we analyzed the size-dependent behavioral responses of an intermediate crab host ( Hemigrapsus crenulatus ) of different sizes to experimental infection by the acanthocephalan parasite Profilicollis chasmagnathi under controlled laboratory conditions. We analyzed 2 behaviors related to the predation risk of crab hosts as a function of their size and infection status: the frequency of exploratory actions and anti-predator behaviors when exposed to predation risk. The frequency of exploratory events was significantly lower in experimentally infected crabs compared to control crabs; however, infection had no detectable effect on crab anti-predator behavior. On the other hand, as crab body size increased, crabs explored more and confronted predators less. These results suggest that, while the behavior of crabs naturally changes throughout ontogeny, the effect of parasite infection on host behavior was smaller and more subtle in this complex host-parasite system.