The songbirds only use their right eye and the left side of their brain when choosing a mate. The research, conducted at Macquarie University in Sydney, provides the first demonstration, in any animal, of visual mate choice taking place in only one side of the brain.
Earlier reports that zebra finches prefer to view mates with the right eye during courtship, and that the immediate genetic response associated with courtship behaviour occurs only in their left hemisphere, suggested to the researchers that visual mate choice itself may also occur in one hemisphere only.
To test this hypothesis, they studied the Gouldian finch, a species in which individuals exhibit strong, adaptive visual preferences for mates of their own head colour.
Black males were tested under three conditions while assessing potential mates: using only their right eye, using only their left eye and using both eyes.
“The black male preference for black females is so strongly lateralized in the right-eye / left-hemisphere system,” says Simon Griffith, one of the authors, “that when using their left eye, males are unable to choose, not only between males and females of the same morph [head-colour], 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 processed using only one side of the brain. Understanding the mechanisms underlying mate choice and identifying the specific brain regions involved may lead to new insights into sexual selection and the evolution of new species.
“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.”