Operant conditioning through positive reinforcement in the ghost crab (Ocypode quadrata)

Ghost crab (Ocypode quadrata) live in dynamic environments filled with numerous conspecifics, predators, and anthropogenic threats. The capacity to learn in these treacherous contexts could drastically improve the chances of survival and, perhaps, reproduction. Operant conditioning encompasses a suite of paradigms all meant to foster the acquisition of predictive relations between stimuli and behavior. Recent evidence suggests ghost crab are capable of relatively complex mental processes, and to add to the known cognitive repertoire evolved in this species, the current research exposed them to an operant conditioning regime. In a "reinforced" condition, animals were placed in a square experimental arena that adjacently positioned a green sticker and false escape hatch covered by a movable door on the same wall. Travel to the green sticker lifted the door to give brief visual access to a sand compartment (i.e. reward) visible through the false hatch. In a control condition, the environment was identical, but view of the sand compartment was yoked to sticker approaches from animals in the reinforced group. Across 3 hours of training, crabs in both conditions significantly increased their sticker approach rates. However, group differences across training blocks emerged and persisted after only 1 hour, such that crabs in the reinforced group displayed significantly higher approach rates compared to yoked controls. An exploratory analysis also revealed that learning rates were correlated positively to carapace size. Thus, this research demonstrates that ghost crabs are able to learn through positive reinforcement, and this skill is one that may develop across the lifespan.