Abstract
Early-life experiences can shape adult behavior, with consequences for fitness and health, yet fundamental questions remain unanswered about how early social environments and experiences are translated into variation in brain and behavior. The African cichlid fish Astatotilapia burtoni, a model system in social neuroscience, is well known for its highly plastic social phenotypes in adulthood. Here, we rear juveniles in either social groups or pairs to investigate the effects of early-life social environments on behavior and neuroendocrine gene expression. We find that both juvenile behavior and neuroendocrine function are sensitive to early-life social effects. Behavior robustly co-varies across multiple contexts (open field, social cue investigation, and dominance behavior assays) to form a behavioral syndrome. Rearing environment shifts pair-reared juveniles towards the end of syndrome that is less active and socially interactive. Pair-reared juveniles also submit more readily as subordinates. In a separate cohort, we then measured neural expression for stress and sex hormone genes, signaling systems known to be developmentally plastic and involved in translating environmental conditions into biological responses and regulating adult social behavior. Rearing environment causes striking differences in neuroendocrine gene co-expression networks. Specifically, expression was tightly integrated in pair-reared juveniles, but not group-reared or isolated juveniles. Glucocorticoid receptor subtypes 1a, 1b, and 2, as well as androgen receptor α, drive the significant differences between treatment groups, which supports a highly conserved role for the stress axis mediating early-life effects. Together, this research demonstrates the important developmental origins of behavioral phenotypes and identifies potential behavioral and neuroendocrine mechanisms.