The eyes have it: genetic, morphological and functional analysis of differences in compound eyes between Drosophila species

视觉是帮助动物在环境中导航的主要感觉系统之一。动物的眼睛有很大的差异，反映了行为和栖息地的进化适应。决定视觉质量的两个主要参数是：1)物体在不同亮度下的区分难易程度（对比敏感度）和2)两个物体之间的距离要有多远才能被区分（敏锐度）。对比敏感度取决于眼睛的光感受器吸收的光量，因此取决于眼睛的大小和光感受器的敏感度。另一方面，敏锐度取决于那些光敏感光器的密度，例如，人眼视网膜中杆状细胞和锥状细胞的密度。同样的规则也适用于昆虫的复眼，它们是由更小的眼睛组成的，称为小眼。更大的裸眼与更大的透镜直径来收集光子提供更高的对比灵敏度。然而，敏锐度取决于小眼的密度——每眼面积的小眼越多，敏锐度就越高，因此在对比敏感度和由小眼的大小和数量决定的敏锐度之间可能存在权衡。昆虫的小眼大小和眼睛的整体大小差异很大，但我们对这些进化差异背后的基因知之甚少，这是如何改变眼睛的发育的，以及这些眼睛形态的变化是如何改变这些动物的视力的。我们发现，正齿基因（otd）导致毛利亚果蝇和拟象果蝇之间的小眼直径和整体眼睛大小的差异。我们现在建议使用一系列的方法来了解otd如何调节小眼的大小，以及这种基因如何使毛里求斯鬣蜥的眼睛变大，以及对它们视力的影响。我们将首先进一步研究otd在模式生物黑腹龙小孔虫大小调控中的作用，以进一步了解其机制。然后，我们将D.毛里求斯版本的od放入D.拟像的遗传背景中，反之亦然，结果D.拟像的苍蝇与D.毛里求斯一样的眼睛，反之亦然。然后可以将这些果蝇与纯模拟D.和毛里求斯D.果蝇在眼睛发育、眼睛形态、神经元活动和实际视力方面的调节进行比较。这些实验的结果将揭示自然基因变异如何改变眼睛的发育，从而产生具有不同光学结构的眼睛，以及这如何影响这些果蝇的视力。这将有助于我们更好地了解昆虫的视觉，并为昆虫眼睛的多样性和这些动物的视觉是如何进化的提供新的见解。此外，由于无脊椎动物和脊椎动物的眼睛发育有很大的相似之处，包括otd及其同源物的重要作用，该项目可以为包括人类在内的动物的眼睛发育提供更广泛的新信息。

Vision is one of the major sensory systems that helps animals navigate through the environment. There is great variation among the eyes of animals reflecting evolutionary adaptations in behaviour and habitat. Two major parameters that determine the quality of vision are: 1) How easily can objects be discriminated at different levels of light luminescence (contrast sensitivity) and 2) how far apart do two objects have to be to be detected discriminated (acuity). Contrast sensitivity depends on the amount of light absorbed by the eye's photoreceptors and therefore on the size of the eye and photoreceptor sensitivity. Acuity on the other hand depends on the density of those light-sensitive photoreceptors, for example, the density of rods and cones in the retina of the human eye. The same rules generally apply to the compound eyes of insects, which are made up of smaller eyes, called ommatidia. Larger ommatidia with larger lens diameters to collect photons gives higher contrast sensitivity. However, acuity depends on the density of ommatidia - more ommatidia per eye area gives higher acuity, and therefore there can be a trade off between contrast sensitivity and acuity determined by the size and number of ommatidia. The size of ommatidia and overall eye size varies greatly among insects, but we still know very little about the genes underlying these evolutionary differences, how this changes the development of eyes, and how these changes in eye morphology alter the vision of these animals. We have found that the gene orthodenticle (otd) causes differences in ommatidia diameter and overall eye size between the closely related species Drosophila mauritiana and Drosophila simulans. We now propose to use a range of approaches to understand how otd regulates ommatidia size and how this gene makes larger eyes in D. mauritiana, and the consequences for their vision. We will first further study the role of otd in specification of ommatidia size in the model organism D. melanogaster to learn more about the mechanisms involved. We will then put the D. mauritiana version of otd into a D. simulans genetic background and vice versa, resulting in a D. simulans fly with a D. mauritiana-like eye and the other way around. These flies can then be compared to pure D. simulans and D. mauritiana flies in their regulation of eye development, eye morphology, neuronal activity and their actual vision. The results of these experiments will reveal how natural genetic variation alters eye development to produce eyes with different optics and how this affects the vision of these flies. This will help us to better understand insect vision generally and provide new insights into how the great diversity of insect eyes and the vision of these animals have evolved. In addition, since there are major similarities between invertebrate and vertebrate eye development, including important roles of otd and its homologues, this project could provide new information about eye development more broadly in animals including humans.