Effect of previous social condition on memory formation in crabs Neohelice granulata.

Social interaction in animals affects nervous system development and behaviors such as aggressiveness and sleep, among others. In the crab Neohelice granulata, long-term memory is impaired in males isolated from conspecifics for at least 6 days. However, this manipulation has not been tested in females, and potential sex differences regarding interaction between social condition and cognitive performance remain unknown. Memory in Neohelice granulata has typically been studied in males by recording their escape response to a visual danger stimulus. Repeated spaced presentation of this stimulus elicits a decrease in the escape response in trained animals relative to controls, a reduction that persists for several days, indicating long-term memory retention. In the present study, we assessed spontaneous activity, initial escape response, learning rate and long-term memory (24 h) in both male and female crabs, maintained under isolated or social (N = 20 crabs, same sex) conditions for 7 days before training. Because wild N. granulata live at high densities, social interaction may represent a natural condition. However, animals can spend variable periods confined to their burrows depending on the season. Studying isolation effects may link social condition to previously reported circannual changes in cognitive performance.