Stream grazers determine their crawling direction on the basis of chemical and visual/tactile microalgal cues

This study aimed to determine the association of herbivore behavior with cues from producers. We used stream grazer Glossosoma larvae and determined their crawling direction in relation to the chemical and visual cues from microalgae. The experimental treatments included control (no cue), particulate (chemical and visual/tactile cues), and dissolved (chemical cue) cues from microalgae. The experimental water samples were randomly placed into either arms of a Y-shaped channel, and the crawling direction of the grazers was determined. Although the grazers crawled toward the arm containing either particulate or dissolved cues, they preferred the arm with particulate cues. This suggested that grazers responded well when both visual/tactile (i.e., drifting algal cells) and chemical cues (algal smell) were present, and that visual/tactile cues were more important for foraging. In natural habitats, grazers detect cues from both producers and predators and use them to maximize fitness by avoiding predation and obtaining food.