Multimodal Sensory Control of Exploration by Walking Drosophila melanogaster

Walking fruit flies, Drosophila melanogaster, use visual information to orient towards salient objects in their environment, presumably as a search strategy for finding food, shelter or other resources. Less is known about the role of vision or other sensory modalities in the evaluation of objects once they have been reached. In order to study these behaviors, I developed a large arena in which I could track individual fruit flies as they walk through either simple or more topologically complex landscapes. Flies use visual cues from the distant background to stabilize their walking trajectories. When exploring an arena containing objects, flies actively orient towards, climb onto, and explore the objects, spending most of their time on the tallest, steepest object. A fly’s behavioral response to an object’s geometry depends upon the intrinsic properties of each object and not an assessment relative to other nearby objects. Further, the preference is due to a change in locomotor behavior once a fly reaches and explores the object’s surface. Specifically, flies are much more likely to stop walking for long periods on tall, steep objects. Both the visual and the antennal mechanosensory systems provide sufficient information about an object’s geometry to elicit the observed change in locomotor behavior. Only when both these sensory systems are impaired do flies not show the behavioral preference for the tall, steep objects. Additionally, I examined the locomotor and social behaviors of large groups of flies. In order to do these studies, I assisted in the development of automated software for tracking and maintaining the individual identity of large groups of flies and for the quantification of individual flies’ locomotor and social behaviors. Behavioral differences between individuals are consistent over the time of the trials and are sufficient to predict a fly’s gender (male vs. female), genotype (wild type vs. fruitless), or sensory environment (with vs. without visual cues). During encounters, males approach other flies more closely than do females and are most often located behind the other fly. The software developed is publicly available and represents a new level of automated quantification in behavioral studies of flies