Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.
PLoS One. 2013 Jun 12;8(6):e65509. doi: 10.1371/journal.pone.0065509. Print 2013.
Domestication processes tend to release animals from natural selection and favour traits desired by humans, such as food-production and co-operative behaviour. A side effect of such selective breeding is the alteration of unintended traits. In this paper, we investigate how active selection for egg production in chickens has affected the visual system, in particular the optical sensitivity that relates to the ability of chickens to see in dim light. We measured eye dimensions as well as the pupil diameter at different light intensities (the steady state pupil dynamics), in adult male and female White Leghorns and the closest relatives to their ancestor, the Red Junglefowls. With this information, we calculated the focal length and optical sensitivity (f-number) of the eyes. Males have larger eyes than females in both breeds and White Leghorn eyes are larger than those of Red Junglefowls in both sexes. The steady state pupil dynamics is less variable, however, the combination of pupil dynamics and eye size gives a higher optical sensitivity in Red Junglefowl eyes than in White Leghorns at light intensities below approximately 10 cd/m(2). While eye size and focal length match the larger body size in White Leghorns compared to Red Junglefowls, the steady state pupil dynamics do not. The reason for this is likely to be that eye morphology and the neuro-muscular control of the pupil have been affected differently by the strong selection for egg production and the simultaneous release of the selection pressure for high performing vision. This study is the first description of how optical sensitivity has changed in a domesticated species and our results demonstrate important considerations regarding domestication processes and sensory ability.
驯化过程往往使动物摆脱自然选择的影响，而有利于人类所期望的特征，例如生产食物和合作行为。这种选择性繁殖的一个副作用是改变了非预期的特征。在本文中，我们研究了在鸡中为提高产蛋量而进行的积极选择如何影响视觉系统，特别是与鸡在暗光下的视力能力相关的光学敏感性。我们测量了成年雄性和雌性白来航鸡和它们祖先红原鸡的眼睛尺寸以及不同光强下的瞳孔直径（稳态瞳孔动力学）。利用这些信息，我们计算了眼睛的焦距和光学敏感性（f-数）。在这两个品种中，雄性的眼睛都比雌性大，而在这两个性别中，白来航鸡的眼睛都比红原鸡的眼睛大。然而，稳态瞳孔动力学的变化较小，但是，结合瞳孔动力学和眼睛大小，在光强低于约 10 cd/m2 时，红原鸡的眼睛比白来航鸡具有更高的光学敏感性。虽然眼睛大小和焦距与白来航鸡相比，红原鸡的体型较大相匹配，但稳态瞳孔动力学并不匹配。造成这种情况的原因可能是眼睛形态和瞳孔的神经肌肉控制受到强烈的产蛋选择和高视觉表现选择压力的释放的不同影响。本研究首次描述了光学敏感性在驯化物种中是如何变化的，我们的研究结果表明了驯化过程和感官能力的重要考虑因素。
