One of the fundamental questions in biology is how animals form affiliative bonds. In particular, what are the neural mechanisms by which these bonds are made and are these basic mechanisms conserved across vertebrate species? The prairie vole has given clues to some of the neurotransmitter systems that are important for pair-bond formation1,2,3. In particular, dopamine acting through receptors in the nucleus accumbens can induce partner preference in both male and female voles4,5. It is unclear whether the general principles underlying partner preference formation and maintenance are evolutionarily conserved.
Monogamy is more common in birds than in mammals6. Therefore, comparing mechanisms of affiliative behavior in birds to other species is critical to understanding conserved neural foundations7,8,9. In general, across many species of songbirds, male song is thought to serve as an honest indicator of male fitness10,11. Male zebra finch songbirds sing to attract mates and influence the formation of monogamous pairs12,13. Thus, song can be used to determine partner preference in these birds.
The mechanisms by which females form a preference for their partner's song is unknown. Mesotocin, the avian homologue of oxytocin, appears to play a role in pair-bond formation in finches14,15. In addition, dopamine has also been shown to play a role in pair-bond formation9,16,17,18. For example, dopamine levels are higher in the nucleus accumbens of paired versus non-paired finches9.
To study the role of neurotransmitter systems on pair-bond formation and maintenance, we measured song preference using an operant testing paradigm equipped with infrared sensors to trigger song playbacks19. The ratio of song playbacks identified the female's preference for a male's song. Prior to the operant conditioning task, each female was isolated for up to 48 h in an anechoic chamber with her partner for 'paired females' or with an unfamiliar male, for 'unpaired females'. To test the effect of dopamine on song preference, unpaired females were treated twice with a D2R dopamine agonist while isolated with the unfamiliar male. This behavioral paradigm is based on previous studies19,20 and is amenable to research by undergraduate students.