Sensory discrimination of chemical and temperature stimuli in the acoel Symsagittifera roscoffensis

Environmental cues provide critical sensory information for the survival of animals. Understanding how distinct sensory cues elicit or modulate certain behaviour thus provides insights into the neuronal adaptations to rapid and continuous changes in the surrounding world. Intertidal ecosystems are a particularly exposed to environmental fluctuations. Due to changing exposure to seawater, animals are subjected to continuous fluctuations of temperature or salinity during the course of day-night and tidal cycles. Animals in the intertidal environment show physiological and behavioural adaptations to these changes. When the acoel Symsagittifera roscoffensis is exposed to daylight during the tidal cycle, these animals are found at the surface of sandy beaches, which enhance the exposure of their photosynthetic algal (Tetraselmis convolutae) symbionts to light. Moreover, S. roscoffensis shows a strong positive phototactic displacement as well as both positive and negative geotaxis, both being evolved behavioural adaptations to enhance light-exposure for its photosymbiont. Currently little is known about other sensory systems and their functions in S. roscoffensis. In this study, we probe sensory capabilities of S. roscoffensis focusing on chemical and temperature cues. Our findings support that S. roscoffensis shows avoidance behaviours to increased temperature and high salinity, preferring cooler environments with lower salinity.