Real or fake? natural and artificial social stimuli elicit divergent behavioral and neural responses in mangrove rivulus, Kryptolebias marmoratus

Understanding how the brain processes social information and generates adaptive behavioural responses is a major goal in neuroscience. We examined behaviour and neural activity patterns in socially relevant brain nuclei of hermaphroditic mangrove rivulus fish (Kryptolebias marmoratus) provided with different types of social stimuli: stationary model opponent, regular mirror, non-reversing mirror and live opponent. We found that: i) individuals faced with a regular mirror were less willing to interact with, delivered fewer attacks towards, and switched their orientation relative to the opponent more frequently than fish exposed to a non-reversing mirror image or live opponent; ii) fighting with a regular mirror image caused higher expression of immediate-early genes (IEGs: egr-1 and c-Fos) in the teleost homologs of the basolateral amygdala and hippocampus but lower IEG expression in the preoptic area than fighting with a non-reversing mirror image or live opponent; iii) stationary model...