From encounter to memory: molecular dynamics of heterospecifc recognition in cleaner wrasse

Heterospecific individual recognition, the capacity to identify and remember specific members of another species, guides partner choice in mutualisms, reduces costly misclassification, and supports community stability. Yet the molecular machinery enabling such recognition is poorly understood. The cleaner wrasse Labroides dimidiatus makes heterospecific individual recognition a central feature of its behavioural ecology, through ~ 2,300 daily interspecific interactions it has developed the ability to assess and recall partners rapidly and accurately. To probe the molecular basis of this capacity, we coupled a familiar–unfamiliar two-choice social preference test with forebrain RNA-sequencing and H3K27ac profiling at 0, 30, and 120 min, linking behaviour, transcription, and chromatin state. Behaviourally, familiarisation reduced time spent near the familiar client. At the molecular level, transcriptomes traced a phased trajectory: an immediate dampening of synaptic release and chemosensory drive, a 30-min GABAergic/homeostatic adjustment, and a 120-min consolidation marked by adhesion and dendritic spine remodelling. Chromatin profiling revealed broad baseline accessibility with only modest between-condition differences and stronger within-condition temporal shifts, indicating that chromatin supports, rather than drives, transcriptional change. Overall, this work offers a molecular framework for heterospecific recognition, linking fast circuit tuning to the subsequent stabilisation of social information.