Data from: Evolution of eye morphology and rhodopsin expression in the Drosophila melanogaster species subgroup

A striking diversity of compound eye size and shape has evolved among insects. The number of ommatidia and their size are major determinants of the visual sensitivity and acuity of the compound eye. Each ommatidium is composed of eight photoreceptor cells that facilitate the discrimination of different colours via the expression of various light sensitive Rhodopsin proteins. It follows that variation in eye size, shape, and opsin composition is likely to directly influence vision. We analyzed variation in these three traits in D. melanogaster, D. simulans and D. mauritiana. We show that D. mauritiana generally has larger eyes than its sibling species, which is due to a combination of larger ommatidia and more ommatidia. In addition, intra- and inter-specific differences in eye size among D. simulans and D. melanogaster strains are mainly caused by variation in ommatidia number. By applying a geometric morphometrics approach to assess whether the formation of larger eyes influences other parts of the head capsule, we found that an increase in eye size is associated with a reduction in the adjacent face cuticle. Our shape analysis also demonstrates that D. mauritiana eyes are specifically enlarged in the dorsal region. Intriguingly, this dorsal enlargement is associated with enhanced expression of rhodopsin 3 in D. mauritiana. In summary, our data suggests that the morphology and functional properties of the compound eyes vary considerably within and among these closely related Drosophila species and may be part of coordinated morphological changes affecting the head capsule.

昆虫类群中，复眼（compound eye）的尺寸与形态演化出了极为丰富的多样性。小眼（ommatidia）的数量与自身尺寸，是决定复眼视觉灵敏度与空间分辨率的核心因素。每个小眼由8个感光细胞构成，这些细胞通过表达多种光敏感视紫红质（rhodopsin）蛋白，辅助完成不同色彩的辨别。由此可见，复眼尺寸、形态以及视蛋白（opsin）组成的差异，极有可能直接影响视觉功能。我们针对黑腹果蝇（D. melanogaster）、拟暗果蝇（D. simulans）以及毛里求斯果蝇（D. mauritiana）的上述三项性状差异展开了分析研究。结果显示，毛里求斯果蝇的复眼尺寸普遍大于其近缘姊妹物种，这一特征源于小眼尺寸更大且小眼数量更多的双重作用。此外，拟暗果蝇与黑腹果蝇各品系间的种内及种间复眼尺寸差异，主要由小眼数量的变化所主导。我们采用几何形态测量学（geometric morphometrics）方法，探究复眼尺寸增大是否会对头壳（head capsule）的其他区域产生影响，结果发现复眼尺寸增加与相邻面部表皮（face cuticle）的面积缩减存在显著关联。形态分析还表明，毛里求斯果蝇的复眼在背侧区域出现了特异性增大。值得注意的是，这种背侧复眼增大与毛里求斯果蝇体内视紫红质3（rhodopsin 3）的表达上调存在相关性。综上，我们的研究数据表明，在这些近缘果蝇（Drosophila）物种内部及物种之间，复眼的形态与功能特性存在显著差异，这可能属于影响头壳整体发育的协同性形态变化的一部分。