Chemical cues from fish, or kairomones, often impact the behavior of zooplankton. These behavioral changes are thought to improve predator avoidance. For example, marine and estuarine crustacean zooplankton become more sensitive to light after kairomone exposure, which likely deepens their vertical distribution into darker waters during the day and thereby reduces their visibility to fish predators. Here, we show that kairomones from an estuarine fish induce similar behavioral responses in adult brine shrimp (Artemia franciscana) from an endorheic, hypersaline lake, Great Salt Lake, Utah, USA. Given downwelling light stimuli, kairomone-exposed A. franciscana induce a descent response upon dimmer light flashes than they do in the absence of kairomones. Using extracellular electroretinogram (ERG) recordings, we also find that kairomones induce physiological changes in the retina that may lead to increased visual sensitivity, suggesting that kairomone-induced changes to photobehavior are mediated at the photoreceptor level. However, kairomones did not induce structural changes within the eye. Although A. franciscana inhabit endorheic environments that are too saline for most fish, kairomones from an estuarine fish amplify photobehavior in these branchiopod crustaceans. The mechanism for this behavioral change has both similarities to and differences from that described in marine malacostracan crustaceans.
Keywords: Artemia franciscana; Phenotypic plasticity; Photobehavior; Vision; Zooplankton.