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The genetic basis of an exaggerated sexual ornament in the stalk-eyed fly Teleopsis dalmanni

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Stalk-eyed flies get hooked on the females

Large male stalk-eyed flies have an overstated eye span, which appears to work well as a sexual ornament to attract females.

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Stalk-eyed flies have eyes on elongated stalks at each side of their head. The Genorn project partners carried out laboratory and field research using state-of-the-art molecular techniques to measure and map genetic differences in the eye span of male stalk-eyed flies. The particular fly under the microscope was the Teleopsis dalmanni. Preliminary research suggests that sexually exaggerated male eye span may work as a sign of genetic quality, to attract females. Samples were collected from the Malaysian rain forest And their DNA was extracted. In one group of 500 adult flies collected from 11 streams in one valley it was found that meiotic drive – preferential production of germ cells – may bring about a distortion of linked genetic markers or genes that are modifiers of drive. The second group of 1\;000 samples was made up of females and all their offspring collected from six streams. They were all genotyped and, using microsatellites, sex was assigned to the offspring and sex ratio differences between families were established. In a third laboratory-based experiment, collected males were mated with laboratory-bred females. Early on in the project, it was discovered that large T. dalmanni males had leg hooks on their forelimbs. Small males and females do not have this characteristic. Male stalk-eyed flies use their legs to threaten rivals and to bring a fight to a conclusion. Genorn designed experiments and held contests to examine the function of the leg hook. Results indicate the hook can be used to threaten an opponent during a non-contact stage, as well as to hold on to an opponent. It is noteworthy that a detailed morphological analysis of the leg hook strongly correlated with eye-span and body size. Further detailed anatomical studies showed that the internal structures of the leg help reduce the power needed to keep the legs closed, and therefore help in holding on to the opponent's leg.

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