Conservation of the expression of Dll, en, and wg in the eye‐antennal imaginal disc of stalk‐eyed flies

SUMMARY We studied the developmental basis of exaggerated eye span in two species of stalk‐eyed flies ( Cyrtodiopsis dalmanni and Sphyracephala beccarri ). These flies have eyes laterally displaced at the end of eyestalks, and males have greatly exaggerated eye span, which they use as a sexual display. To investigate eye span development we have compared eye‐antennal disc morphology and the expression of three key regulator genes of Drosophila head development, Distal‐less ( Dll ) , engrailed ( en ), and wingless ( wg ), in the stalk‐eyed flies and Drosophila . We found great similarity in the basic division of the disc into anterior‐antennal and posterior‐eye portions and in the general patterning of Dll, en , and wg . Unexpectedly, our results showed that although the eye and antenna are adjacent in adult stalk‐eyed flies, their primordia are physically separated by the presence of an intervening region between the anterior and posterior portions of the disc. This region is absent from Drosophila eye‐antennal discs. We chose two stalk‐eyed fly species that differed in the degree of eyestalk exaggeration but surprisingly we found no corresponding difference in the size of the en‐wg expression domains that mark the boundaries of the dorsal head capsule primordia. In summary, our expression data establish the regional identity of the eye‐antennal disc and provide a framework from which to address the developmental genetics of hypercephaly.