Cognitive ethology of nest building in a shell-dwelling cichlid

Across animal taxa, nest-building behavior is performed using a generalizable and flexible action sequence. In order to accomplish its goal (a stable nest), the brain appears to compare intermediate steps in the process to stored neural representations that are reminiscent of cognitive templates. Deviations from these templates drive progress, preferences, and corrections in the execution of this behavior. Here, we investigated the stereotypy vs. plasticity of nest building by the cichlid Lamprologus ocellatus, a fish species that manipulates abandoned snail shells to build shelters for breeding and protection. We find that nest building is composed of a sequence of behaviors that are tied together by a series of stimulus-response loops, allowing for restarts and shortcuts as the behavioral program unfolds. The attraction to a shell object is innate, as is the final appearance of the nest. The behavior of an inexperienced animal is initially uncoordinated but is fine-tuned by repeated building opportunities. Shells need to conform to rigid geometric criteria in order to be acceptable as a potential home. Nest building is accompanied by focused neural activity in brain regions homologous to the mammalian hippocampus and neocortex. In conclusion, we have uncovered the constraints and flexibility of an instinctive, goal-directed behavior, which appears to employ cognitive template matching. VIDEO ABSTRACT.