Modular genetic control of social status in a cichlid fish

Social hierarchies are ubiquitous in social species, yet the mechanisms underlying social status are unclear. In the African cichlid fish Astatotilapia burtoni, males stratify along a dominance hierarchy that varies based on testes mass, coloration, and behavior. Using androgen receptor (AR) mutant A. burtoni generated using CRISPR/Cas9, we find that two AR genes control social dominance. ARβ, but not ARα, is required for testes growth and bright coloration, while ARα, but not ARβ, is required for the performance of reproductive behavior and aggressive displays. Neither receptor is required for attacking males. Analysis of AR double mutants revealed that either AR is sufficient for attacking males. Social status in A. burtoni males is modularly controlled by ARα and ARβ, indicating that these genes have undergone subfunctionalization.