Tameness can be divided into two components: active tameness and passive tameness. We conducted selective breeding for higher scores of active tameness using a wild-derived heterogeneous stock. In the analyses of nine behavioral traits related to tameness, we found that five traits showed changes in the selective groups compared to the control groups through the generations. We conducted cluster analyses to evaluate the relationship among the nine traits and RNA-Seq analysis to characterize the molecular network related to tameness. The results suggested that active tameness was hidden in the control groups but became apparent in the selected populations by selective breeding, potentially driven by changes in gene expression networks.

Figure: The wild-derived heterogeneous stock was divided into four groups, two groups were selected for active tameness, and the other two groups were unselected controls. A: As the generation progressed, active tameness increased in the two selection groups, whereas there was no significant increase in the two control groups. B: RNA-seq analysis was performed using samples collected from the brains (hippocampus) of mice in the selection groups and the control groups. As a result, genes with different expression levels were found in the selection groups and the control groups, and differences in the gene network were also found.