Experience-dependent plasticity of the optomotor response in Drosophila melanogaster.

Experience in early life can affect the development of the nervous system. There is now evidence that experience-dependent plasticity exists in adult insects. To uncover the molecular basis of plasticity, an invertebrate model, such as Drosophila melanogaster, is a powerful tool, as many established genetic and molecular methods can be applied. To establish a model system in which behavioral plasticity can be examined, we investigated the optomotor response, a behavior common to most sight-reliant animals, in Drosophila and found that the response could be modified by the level of light during rearing. The angle turned by the head in response to a moving stimulus was used to quantify the response. Deprivation of light increased the response to low-contrast stimuli in wild-type Drosophila at 4 days after eclosion and this plastic change did not appear in rutabaga, a known mutant defective in short-term memory. In addition, the change was transient and was markedly decreased at 6 days after eclosion. Further, we found that Dark-flies, which have been kept in constant darkness for more than 50 years, showed a higher response to low-contrast stimuli even at 6 days after eclosion compared to wild type and this characteristic was not lost in Dark-flies placed in a normal light environment for 2 generations, suggesting that this high response has a hereditary nature. Thus, our model system can be used to examine how the environment affects behaviors.

A novel behavioral strategy, continuous biased running, during chemotaxis in Drosophila larvae.

Animals collect and integrate information from their environment, and select an appropriate strategy to elicit a behavioral response. Here, we investigate the behavioral strategy employed by Drosophila larvae during chemotaxis toward a food source functioning as an attractive odor source. In larvae, sharp turns have been identified as the main strategy during locomotion to odorant sources, but the existence of runs orienting toward the direction of higher odor concentrations has not been described. In this study, we show the existence of such a successive orientation toward an odor source, which we term as biased running. Our behavioral analysis, which examines the relationship between larval rotational velocities and larval positions relative to an attractive odor source, brings out this newly found behavioral strategy. Additionally, theoretically estimated concentration gradients of chemoattractants between left and right olfactory organs were statistically correlated with rotational velocities during biased running. Finally, computer simulations demonstrated that biased running enhances navigation accuracy. Taken together, biased running is an effective behavioral strategy during chemotaxis, and this notion may provide a new insight on how animals can efficiently approach the odor source.