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Hide if you cannot fly: behavioral plasticity in flightless Drosophila
AuthorBjörn Brembs
Author email bjoern©brembs.net
Author websitehttp://brembs.net
DescriptionAbout one hundred years ago, a student of T.H. Morgan's clipped the wings of flies and tested their response to light. He discovered a reduced phototaxis in flies with clipped wings. Robert McEwen added in his 1918 study that antennae clipping and even leg clipping had smaller effects than wing clipping, showing the specificity to wing clipping. McEwen also tested mutants with non-functional wings and reported that cutting the wings of these flightless flies did not decrease their phototaxis. In 1963, Chiang correlated phototaxis behavior with flying abilities, by looking at the development of both traits in juveniles and compared them with adults: young flies with still un-expanded wings prefer shaded areas over lit ones, with a reversal of the preference at about 7h after emergence. Finally, in 1967, Benzer presented his counter-current apparatus mass-assay for phototaxis behavior. He was also able to confirm that flightless flies show reduced phototaxis scores. What is the neurobiological mechanism by which flies modify their response to light when they are unable to fly?
We first used Benzer’s counter-current apparatus in different modes in order to reproduce the results of McEwen. We found that flightless flies are less attracted to the light even when tested together with flies that can fly. Flies with glued wings return to their normal phototaxis response when their wings are unglued, demonstrating the reversibility of the effect. We performed different control experiments to show that this change in behavior was not due to a locomotion deficit. For instance, we tested the response of flies when the light was coming from other directions or in complete darkness. We also found that flies without wings are more active in a modified Buridan’s paradigm and are heading for the targets more consistently. Flightless mutants with or without apparent wing defect do not show a further reduction in phototaxis. This behavioral plasticity is a very robust phenotype as the standard mutants and transgenes affecting synaptic plasticity and/or learning and memory are unaffected in this experiment. These results are consistent with the hypothesis that flies continuously monitor their flight ability and change the way they respond to sensory cues according to their flight ability at the time the sensory stimulus is perceived. This hypothesis is consistent with recent results showing that altering the state of the animal drastically alters the way it processes sensory information.
We are now screening for flying mutant flies which do not show any decrement in phototaxis after wing clipping, in order to decipher the neuronal mechanisms involved in this behavioral modification.
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