SUMMARY Many motile organisms localize the source of attractive odorants by following plumes upwind. In the case of D. melanogaster, little is known of how individuals alter their flight trajectories after encountering and losing a plume of an attractive odorant. We have characterized the three-dimensional flight behavior of D. melanogaster in a wind tunnel under a variety of odor conditions. In the absence of olfactory cues, hungry flies initiate flight and display anemotactic orientation. Following contact with a narrow ribbon plume of an attractive odor, flies reduce their crosswind velocity while flying faster upwind, resulting in a surge directed toward the odor source. Following loss of odor contact due to plume truncation, flies frequently initiate a stereotyped crosswind casting response, a behavior rarely observed in a continuous odor plume. Similarly, within a homogeneous odor cloud, flies move fast while maintaining an upwind heading. These results indicate both similarities and differences between the behavior of D. melanogaster and the responses of male moths to pheromone plumes,suggesting possible differences in underlying neural mechanisms.

t has long been known that many flying insects use visual cues to orient with respect to the wind and to control their groundspeed in the face of varying wind conditions. Much less explored has been the role of mechanosensory cues in orienting insects relative to the ambient air. Here we show that Drosophila melanogaster, magnetically tethered so as to be able to rotate about their yaw axis, are able to detect and orient into a wind, as would be experienced during forward flight. Further, this behavior is velocity dependent and is likely subserved, at least in part, by the Johnston's organs, chordotonal organs in the antennae also involved in near-field sound detection. These wind-mediated responses may help to explain how flies are able to fly forward despite visual responses that might otherwise inhibit this behavior. Expanding visual stimuli, such as are encountered during forward flight, are the most potent aversive visual cues known for D. melanogaster flying in a tethered paradigm. Accordingly, tethered flies strongly orient towards a focus of contraction, a problematic situation for any animal attempting to fly forward. We show in this study that wind stimuli, transduced via mechanosensory means, can compensate for the aversion to visual expansion and thus may help to explain how these animals are indeed able to maintain forward flight.

Swimming and turning behaviors of larval zebrafish have been described kinematically, but prey capture behaviors are less well characterized. High-speed digital imaging was used to record the axial kinematics of larval zebrafish as they preyed upon paramecia and also during other types of swimming. In all types of swim bouts, a series of traveling waves of bending is observed and these bends propagate along the trunk in the rostral to caudal direction. The prey capture swim bouts appeared to be more complex than other swim patterns examined. In the capture swim bouts, the initial bends were of low amplitude and were most prominent at far-caudal locations during each individual traveling wave of bending. Later bends in the bout (occurring just prior to prey capture) appeared to originate more rostrally and were of larger amplitude. These changes in bending pattern during capture swims were accompanied by a marked increase in tail-beat frequency. Associated with these axial kinematics were changes in heading and an abrupt increase in velocity close to the moment of prey capture. These changing patterns of bending suggest precise, bend-to-bend, neural control over both the timing and the rostral-caudal locus of bending. This degree of ‘fine axial motor control’ has not previously been described in the teleost behavioral literature and is notable because it occurs in larval zebrafish, where descending control signals are funneled through the roughly three-hundred neurons that project from brain into spinal cord. These findings will necessitate a significant increase in the complexity of current models of descending motor control in fishes.

Larval zebrafish (Brachydanio rerio) are a popular model system because of their genetic attributes, transparency and relative simplicity. They have approximately 200 neurons that project from the brainstem into the spinal cord. Many of these neurons can be individually identified and laser-ablated in intact larvae. This should facilitate cellular-level characterization of the descending control of larval behavior patterns. Towards this end, we attempt to describe the range of locomotor behavior patterns exhibited by zebrafish larvae. Using high-speed digital imaging, a variety of swimming and turning behaviors were analyzed in 6- to 9-day-old larval fish. Swimming episodes appeared to fall into two categories, with the point of maximal bending of the larva's body occurring either near the mid-body (burst swims) or closer to the tail (slow swims). Burst swims also involved larger-amplitude bending, faster speeds and greater yaw than slow swims. Turning behaviors clearly fell into two distinct categories: fast, large-angle escape turns characteristic of escape responses, and much slower routine turns lacking the large counterbend that often accompanies escape turns. Prey-capture behaviors were also recorded. They were made up of simpler locomotor components that appeared to be similar to routine turns and slow swims. The different behaviors observed were analyzed with regard to possible underlying neural control systems. Our analysis suggests the existence of discrete sets of controlling neurons and helps to explain the need for the roughly 200 spinal-projecting nerve cells in the brainstem of the larval zebrafish.