Host preference of a symbiotic flatworm and its response to conspecific and host mucus

Abstract

Mucus-mediated communication plays a significant role in shaping community dynamics, particularly in marine organisms found in intertidal zones with complex topography. In this study, we investigated the host preference of a flatworm Stylochoplana pusilla, which lives symbiotically with intertidal gastropods, and its responses to the host and conspecific mucus. Our line transect surveys revealed differences in flatworm prevalence among sympatric gastropods, with multiple flatworms found in a single host individual, indicating host preference. The body mucus of gastropods and flatworms was applied to one side of a Petri dish to experimentally determine whether flatworms prefer the mucus-coated side under light and dark conditions. However, contrary to our expectations, the experiments in both light and dark conditions showed that the mucus of none of the host gastropods effectively attracted flatworms, suggesting that mucus-mediated communication may not be the primary factor in establishing host preference, and other ecological factors may play a role. Nonetheless, under dark conditions, flatworms were attracted to conspecific mucus, indicating that they may engage in collective homing behaviour or conspecific aggregation to find a suitable position in the mantle cavity. Overall, our results highlight the complex ecological interactions involved in shaping symbiosis between flatworms and gastropods.