Data from: In the eye of the beholder: visual mate choice lateralization in a polymorphic songbird

Birds choose mates on the basis of colour, song and body size, but little is known about the mechanisms underlying these mating decisions. Reports that zebra finches prefer to view mates with the right eye during courtship, and that immediate early gene expression associated with courtship behaviour is lateralized in their left hemisphere suggest that visual mate choice itself may be lateralized. To test this hypothesis, we used 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: left-monocular, right-monocular and binocular. We found that black male preference for black females is so strongly lateralized in the right-eye/left-hemisphere system that if the right eye is unavailable, males are unable to respond preferentially, not only to males and females of the same morph, but also to the strikingly dissimilar female morphs. Courtship singing is consistent with these lateralized mate preferences; more black males sing to black females when using their right eye than when using their left. Beauty, therefore, is in the right eye of the beholder for these songbirds, providing, to our knowledge, the first demonstration of visual mate choice lateralization.

鸟类会依据羽色、鸣唱与体型选择配偶，但目前对于这类择偶决策背后的具体机制仍知之甚少。有研究报道称，斑胸草雀（zebra finch）在求偶过程中偏好使用右眼观察配偶，且与求偶行为相关的即刻早期基因（immediate early gene）表达在其左侧大脑半球存在偏侧化现象，这提示视觉择偶行为本身可能具有偏侧化特征。为验证这一假说，本研究选用了七彩文鸟（Gouldian finch）——一种具有多态性的鸟类，其个体对头部羽色与自身相同的配偶存在强烈且具有适应性的视觉偏好。研究人员针对黑色型雄性七彩文鸟，在择偶行为实验装置中设置了三种眼部视觉条件（左眼单眼、右眼单眼及双眼视觉）开展实验。实验结果表明，黑色型雄性对黑色型雌性的择偶偏好高度偏侧化于右眼/左侧大脑半球通路：当右眼无法使用时，雄性不仅无法对同羽色形态的雄性与雌性个体产生优先择偶反应，甚至无法识别差异显著的异色形态雌性个体。求偶鸣唱行为也与这类偏侧化择偶偏好相一致：相较于使用左眼时，使用右眼的黑色型雄性会更多地向黑色型雌性发出鸣唱。因此，对于这类鸣禽而言，“美”的确存在于观察者的右眼之中——据我们所知，本研究首次证实了视觉择偶行为的偏侧化现象。