The placement of eyes on insect head is an important evolutionary trait. The stalk‐eyed fly, Cyrtodopsis whitei, exhibits a hypercephaly phenotype where compound eyes are located on lateral extension from the head while the antennal segments are placed inwardly on this stalk. This stalk‐eyed phenotype is characteristic of the family Diopsidae in the Diptera order and dramatically deviates from other dipterans, such as Drosophila. Like other insects, the adult eye and antenna of stalk‐eyed fly develop from a complex eye‐antennal imaginal disc. We analyzed the markers involved in proximo‐distal (PD) axis of the developing eye imaginal disc of the stalk‐eyed flies. We used homothorax (hth) and distalless (dll), two highly conserved genes as the marker for proximal and distal fate, respectively. We found that lateral extensions between eye and antennal field of the stalk‐eyed fly's eye‐antennal imaginal disc exhibit robust Hth expression. Hth marks the head specific fate in the eye‐ and proximal fate in the antenna‐disc. Thus, the proximal fate marker Hth expression evolves in the stalk‐eyed flies to generate lateral extensions for the placement of the eye on the head. Moreover, during pupal eye metamorphosis, the lateral extension folds back on itself to place the antenna inside and the adult compound eye on the distal tip. Interestingly, the compound eye in other insects does not have a prominent PD axis as observed in the stalk‐eyed fly.

中文翻译：

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近缘命运标记同胸标志着茎眼苍蝇拟南芥的侧向延伸。

将目光放在昆虫头上是重要的进化特征。茎眼苍蝇Cyrtodopsis whitei表现出高头症表型，其中复眼位于从头部横向延伸的位置，而触角段则向内放置在茎上。这种茎眼表型是双翅目科双翅目科的特征，与其他双翅类动物（如果蝇）大相径庭。像其他昆虫一样，成年双眼和茎状蝇的触角是由复杂的眼-肾虚盘形成的。我们分析了与实蝇相关的眼睛假想盘的近距（PD）轴中涉及的标记。我们使用了同胸（hth）和远侧（dll），两个高度保守的基因分别作为近端和远端命运的标记。我们发现，茎状苍蝇眼-肾上腺虚像盘的眼球与触角场之间的横向延伸表现出强健的Hth表达。Hth标志着眼睛圆盘中头部的特定命运，以及天线盘中的近端命运。因此，近端命运标记Hth的表达在带有茎的果蝇中演化，从而产生了将眼睛放在头上的横向延伸。此外，在p眼睛变态期间，侧向延伸部会向后折叠，从而将天线置于内部，而成年复眼放在远端尖端。有趣的是，在其他昆虫中，复眼不像在带茎蝇中观察到的那样具有明显的PD轴。