How Drosophila larvae perceive other animals and communicate with each other is currently only partially understood. Moreover, larvae of two distinct Drosophila species avoid to pupate close to larvae of other species but preferentially pupate in the neighborhood of their conspecifics 6. It has also been shown that larvae aggregate to perform cooperative digging which may increase the feeding efficacy on solid food 3, 4, 5. This increases the relative density of conspecifics. Thereby, behavioral changes are instructed to route them to distinct areas in common food sources. Larvae of different species release different cocktails of attractive pheromones 2. Drosophila larvae are attracted to areas already explored by other larvae via a pheromone triggered signaling pathway 2. In many insect clades such as Drosophila, females lay a large number of eggs close to a food source 1 and thus hatching larvae have to cope with other moving larvae and to compete for limited resources. For example, avoiding collisions in densely populated areas requires an appropriate perception of the surrounding and complex locomotion maneuvers. The success of this goal-oriented locomotion strongly relies on the surrounding objects and animals. Most animals move to find their prey or their appropriate mating partners, to avoid competition for resources or to engage in cooperation. Thus, Drosophila larvae evolved means to specify behaviors in response to other larvae. Interestingly, larvae react differently to living, dead or artificial larvae, discriminate other Drosophila species and have an increased bending probability for a short period after the collision terminates. We show that during collision, larval locomotion freezes and sensory information is sampled during a KISS phase (german: Kollisions Induziertes Stopp Syndrom or english: collision induced stop syndrome). To decipher larval locomotion not only before but also during the collision we utilized a two color FIM approach (FIM 2c), which allowed to faithfully extract the posture and motion of colliding animals. Employing frustrated total internal reflection-based imaging (FIM) we first found that larvae visually detect other moving larvae in a narrow perceptive field and respond with characteristic escape reactions. Here we test whether relevant information is perceived before or during larva-larva contacts, analyze its influence on behavior and ask whether larvae avoid or pursue collisions. However, the mechanisms coordinating larval locomotion in respect to other animals, especially in close proximity and during/after physical contacts are currently only little understood. In populations of Drosophila larvae, both, an aggregation and a dispersal behavior can be observed.
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