Stalk-eyed flies of the family Diopsidae have their eyes laterally displaced on the end of head extensions called “eye-stalks”. Diopsids vary in their degree of sexual dimorphism for eyespan (distance between the eyes). In some dimorphic species it has been well established that females preferentially mate with males possessing exaggerated eyespan. With over 150 members, the family Diopsidae is an ideal model system for analysing the evolution and development of exaggerated sexual traits. Progress towards understanding the mechanisms underlying the development of exaggerated eyespan has been significantly hampered by the lack of modern molecular genetic technology in stalk-eyed flies. I have developed a transgenic protocol in Teleopsis dalmanni, a highly dimorphic diopsid species. I selected and tested embryo microinjection procedures. I used excision assays to compare the activity of three potential transposable element vector systems. Minos and piggyBac demonstrated suitable activity in T. dalmanni embryos but mariner did not. Using Minos and the transgene construct Px3-eGFP, I successfully achieved stable germline transformation in T. dalmanni. A number of transgenic lines were created. In one, a single copy of the insertion was seen to segregate with the X chromosome. I used a histological approach to investigate the relative contributions of cell size and cell number to variation in eyespan. I compared estimates of cell size in the eye-stalks of newly eclosed flies among fully fed and nutritionally stressed individuals. For comparison, I assessed cell size in a non-sexually dimorphic organ, the wing. I found that variation in eyespan was explained, at least in part, by variation in cell size. No inherent difference in eye-stalk cell size was detected between the sexes. The implications of the cell size findings and of the future studies made possible by transgenic technology are discussed
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