Streaming for fish? Screen-based social exposure disrupts brain development.

Social interactions form key developmental cues for plasticity in the vertebrate brain. However, few experimental studies disentangle specific aspects of sociality, such as social interactivity, in this context. Here we tested the role of social interactivity in shaping brain development in juvenile guppies (Poecilia reticulata), a social species with high potential for post-birth neuroplasticity. Fish were reared under one of three conditions: (i) interactive live social exposure to conspecifics, (ii) non-interactive screen-based social exposure to prerecorded conspecifics or (iii) minimal social exposure. We then put them through a cognitive task (object permanence), followed by quantification of brain size and brain region size to assess cognitive and morphological plasticity. There were no effects on object permanence performance, but individuals reared under interactive live social exposure had significantly larger relative brain size and relative olfactory bulb size than those reared under non-interactive screen-based social exposure, which were similar to individuals reared under minimal social exposure. These results suggest that interactive live social exposure increases brain size and highlight interactivity as a driver of neural development.