C. elegans as a model for fear-like behaviors
Learned fear has been studied in invertebrates including Aplysia californica and Drosophila melanogaster. Signaling using the biogenic amines dopamine and serotonin are conserved between invertebrates and vertebrates. While Caenorhabditis elegans is a model organism that has been extensively used to study mechanisms of learning and memory in aversive conditioning, these paradigms do not necessarily fall under learned fear. We have created a predator-prey paradigm using Pristionchus as a model predator and C. elegans as the model prey to study learned fear in C. elegans. We found that C. elegans exposed to predator bites over at least six hours begin to leave a food patch and lay eggs away from it. After a twenty-hour exposure period, C. elegans retains this behavior for at least six hours after removal to an arena without any predators, indicating that this behavior can be learned. We found that dopamine signaling is required for the off-lawn leaving and egg-laying behavior. C. elegans deficient in dopamine synthesis are defective in performing the behavior and this defect can be rescued with exogenous dopamine treatment after predator exposure. Additionally, serotonin and mechanosensation appear to play a role in this behavior but their roles are not yet fully investigated.