Behavioral and neural trade-offs between song complexity and stress reaction in a wild and a domesticated finch strain

• Songs of domesticated Bengalese finches are more complex than those of their wild ancestor, the white rumped munia.
• Domestication and sexual selection are two key factors for the evolution of song complexity.
• The wild strain has a higher level of corticosterone than the domesticated strain.
• Glucocorticoid and mineralocorticoid receptors exist in song and emotion areas of the brain.
• A lower stress level in the domesticated strain might lead to higher brain plasticity.

The Bengalese finch is the domesticated strain of the wild white-rumped munia. Bengalese finches have been domesticated and reproductively isolated for over 250 years from the wild strain. During this period, the courtship songs of the domesticated birds became phonologically and syntactically complex. In addition, psychological and physiological stress reactions to environmental and social factors diverged between the two strains. Based on our behavioral and histological studies, we consider the balance between the glucocorticoid- and mineralocorticoid receptors in song control nuclei and in the avian amygdala as to determine whether a bird can develop complex songs or rather has to devote the neural resources for the maintenance of stress reactions. We therefore suggest that phonological and syntactical complexity in Bengalese finch songs initially evolved because domestication freed them from species recognition and environmental stress, and then sexual selection increased the complexity. Neural and molecular studies also support the notion that Bengalese finches keep more song plasticity as adults. In conclusion, the present study suggests that domestication changed factors related with psychobiology of stress reactions and learning in finches.