In a study published in Biology Letters this week, researchers have discovered a unique mechanism used by the Gouldian finch in making the crucial choice of life partner: mate choice with just one eye.
Beauty really is in the eye of the beholder for these songbirds, who use just their right eye and the left side of their brain in mate choice. The research, conducted at Macquarie University, provides the first demonstration of visual mate choice lateralization in any animal.
Earlier reports that zebra finches prefer to view mates with the right eye during courtship, and that the immediate early gene expression associated with courtship behaviour is lateralized in their left hemisphere, suggested to the researchers that visual mate choice itself may be lateralized.
Red male and black female Gouldian finch, credit Sarah Pryke
To test this hypothesis, they studied the Gouldian finch, a polymorphic species in which individuals exhibit strong, adaptive visual preferences for mates of their own head colour.
Black males were tested in a mate-choice apparatus under three eye conditions: leftmonocular, right-monocular and binocular.
“The black male preference for black females is so strongly lateralized in the right-eye / left-hemisphere system,” says Macquarie’s Simon Griffith, “that when using their left eye, males are unable to choose, not only between males and females of the same morph, but also between strikingly dissimilar females.”
The study’s results add mate choice, a process of great adaptive significance, to the extensive list of cognitive and behavioural functions known to be lateralized. Understanding the mechanisms underlying mate choice and identifying the specific brain regions involved may lead to new insights into sexual selection and speciation.
“This work will help us to understand how a complex process, such as determining the attractiveness of a potential partner can be limited to just a single eye, and side of the brain. One of the consequences of this finding is that individuals should approach, and display to a potential mate from the right side, and perhaps this is the reason that many animal displays are side on.”
In the eye of the beholder: visual mate choice lateralization in a polymorphic songbird, Jennifer J. Templeton, D. James Mountjoy, Sarah R. Pryke, Simon C. Griffith. Biology Letters, 2012. doi: 10.1098/rsbl.2012.0830.