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，反映了进化中对行为和栖息地的适应。决定视觉质量的两个主要参数是：1)在不同级别的光发光(对比度敏感度)下辨别物体的难易程度；2)必须检测到两个物体相隔多远才能被辨别(敏锐度)。对比敏感度取决于眼睛感光器吸收的光量，因此取决于眼睛的大小和感光器的敏感度。另一方面，视力取决于感光器的密度，例如，人眼视网膜中视杆细胞和视锥细胞的密度。同样的规则通常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。小眼越大，收集光子的透镜直径越大，对比度越高。然而，视力取决于小眼孔的密度--每眼面积的小眼孔越多，视力就越高，因此可以在对比敏感度和由小眼孔的大小和数量决定的锐度之间进行权衡。不同昆虫的小眼大小和整体眼睛大小差异很大，但我们仍然对这些进化差异背后的基因，这如何改变眼睛的发育，以及这些眼睛形态的变化如何改变这些动物的视力知之甚少。我们发现，OTD基因导致了近缘物种毛果果蝇和拟果蝇在小眼直径和整体眼睛大小上的差异。我们现在建议使用一系列的方法来了解OTD是如何调节小眼大小的，这个基因是如何让毛叶杜鹃的眼睛更大的，以及对他们的视力的影响。我们将首先进一步研究OTD在模式生物体黑腹圆孔大小指定中的作用，以了解更多涉及的机制。然后，我们将把D-mauritiana版本的OTD放入D-Simans的遗传背景中，反之亦然，结果是D-simans飞行时有D-mauritiana一样的眼睛，反之亦然。然后，这些果蝇可以在眼睛发育、眼睛形态、神经活动和实际视力的调节方面与纯仿生果蝇和毛果蝇进行比较。这些实验的结果将揭示自然遗传变异如何改变眼睛的发育，从而产生具有不同光学功能的眼睛，以及这如何影响这些苍蝇的视力。这将有助于我们更好地从总体上了解昆虫的视觉，并为昆虫眼睛的巨大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，该项目可以提供更广泛的关于包括人类在内的动物眼睛发育的新信息。

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.