Displacement experiments provide evidence for path integration in Drosophila

Play-like behavior exhibited by the vinegar fly Drosophila melanogaster

Anecdotal accounts about animals repeatedly exposing themselves to sources of passive movement by engaging with swings, slides, or carousels are generally assumed to be "play." Criteria for play-like behavior require the activity to be (1) of no immediate relevance for survival; (2) voluntary, intentional, and rewarding; (3) non-ethotypical; (4) repeated, yet unstereotyped; and (5) free from stress.1,2 Play-like behavior following these rules is pervasive across the vertebrate subphylum2; recent studies in rats even identified and characterized the involved brain regions.3,4 In invertebrates, sparse reports have so far addressed either social play in parasitoid wasps or spiders,5,6 object play in bumblebees,7 or are anecdotal.1 Contrary to social play or object play, which are thought to train social interaction or muscle/motor skills, respectively, a convincing hypothesis of the adaptive value of voluntary passive movement play-like behavior is currently lacking in any organism. Like other animals, flies are highly sensitive to the direction of gravitational pull,8 hence such intentional passive motion could be sufficient to induce proprioceptive stimulation externally.9 Here, we identify voluntary spinning on a carousel as idiosyncratic play-like behavior in the vinegar fly Drosophila melanogaster: while some flies show spontaneous avoidance, others actively seek stimulation, engaging in repeated, prolonged visits to the carousel. We propose that animals voluntarily expose themselves to external forces, thus intentionally receiving exafferent stimulation. This deliberate, yet indirect, proprioceptive stimulation provides an efficient way to improve self-perception via internal model training and shaping multisensory integration. Importantly, this theoretical framework can now be tested empirically in flies. VIDEO ABSTRACT.

Temporal effects of sugar intake on fly local search and honey bee dance behaviour

Honey bees communicate flight navigational information of profitable food to nestmates via their dance, a small-scale walking pattern, inside the nest. Hungry flies and honey bee foragers exhibit a sugar-elicited search involving path integration that bears a resemblance to dance behaviour. This study aimed to investigate the temporal dynamics of the initiation of sugar-elicited search and dance behaviour, using a comparative approach. Passive displacement experiments showed that feeding and the initiation of search could be spatially and temporally dissociated. Sugar intake increased the probability of initiating a search but the actual onset of walking triggers the path integration system to guide the search. When prevented from walking after feeding, flies and bees maintained their motivation for a path integration-based search for a duration of 3 min. In flies, turning and associated characters were significantly reduced during this period but remained higher than in flies without sugar stimulus. These results suggest that sugar elicits two independent behavioural responses: path integration and increased turning, with the initiation and duration of path integration system being temporally restricted. Honey bee dance experiments demonstrated that the motivation of foragers to initiate dance persisted for 15 min, while the number of circuits declined after 3 min following sugar ingestion. Based on these findings, we propose that food intake during foraging increases the probability to initiate locomotor behaviours involving the path integration system in both flies and honey bees, and this ancestral connection might have been co-opted and elaborated during the evolution of dance communication by honey bees.

Tracking Sugar-Elicited Local Searching Behavior in Drosophila

Foraging behavior is essential for the survival of organisms as it enables them to locate and acquire essential food resources. In Drosophila, hunger triggers a distinct search behavior following the consumption of small quantities of a sugar solution. This report presents a simple experimental setup to study sugar-elicited search behavior with the aim of uncovering the underlying mechanisms. Minute quantities of concentrated sugar solution elicit sustained searching behavior in flies. The involvement of path integration in this behavior has been established, as flies utilize their trajectory to return to the sugar location. The most recent findings provide evidence of temporal modulation in the initiation and intensity of the search behavior after sugar intake. We have also used this setup for artificial activation of specific taste-receptor neurons in the pharynx, which elicits the search behavior. The Drosophila neurogenetic toolkit offers a diverse array of tools and techniques that can be combined with the sugar-elicited search behavior paradigm to study the neural and genetic mechanisms underlying foraging. Understanding the neural basis of hunger-driven searching behavior in flies contributes to the field of neurobiology as a whole, offering insights into the regulatory mechanisms that govern feeding behaviors not only in other organisms but also in humans.

Displacement experiments provide evidence for path integration in Drosophila

Like many other animals, insects are capable of returning to previously visited locations using path integration, which is a memory of travelled direction and distance. Recent studies suggest that Drosophila can also use path integration to return to a food reward. However, the existing experimental evidence for path integration in Drosophila has a potential confound: pheromones deposited at the site of reward might enable flies to find previously rewarding locations even without memory. Here, we show that pheromones can indeed cause naïve flies to accumulate where previous flies had been rewarded in a navigation task. Therefore, we designed an experiment to determine if flies can use path integration memory despite potential pheromonal cues by displacing the flies shortly after an optogenetic reward. We found that rewarded flies returned to the location predicted by a memory-based model. Several analyses are consistent with path integration as the mechanism by which flies returned to the reward. We conclude that although pheromones are often important in fly navigation and must be carefully controlled for in future experiments, Drosophila may indeed be capable of performing path integration.