# Movement and Dispersion Parameters Characterizing the Group Behavior of Drosophila melanogaster in Micro-Areas of an Observation Arena

## TL;DR

This study explores how fruit flies form local groups in different micro-areas and how their movement and dispersion patterns change over time and with genetic mutations.

## Contribution

The study introduces a multi-parameter approach to analyze group behavior in Drosophila across micro-areas, revealing genetic influences on aggregation patterns.

## Key findings

- Wild-type Drosophila showed two distinct movement patterns during light-to-dark transitions and around food resources.
- Mutant flies exhibited altered movement and aggregation behaviors, indicating genetic contributions to group dynamics.
- Parameters like speed, pause duration, and social space varied significantly by micro-area, time, and strain.

## Abstract

Studying local grouping behavior is essential for understanding animals’ social strategies and interactions related to survival and reproduction. It also provides insights applicable to ecological conservation and biotechnological innovation. In this study, after digitizing the continuous movements of Drosophila melanogaster for a whole day, we examined whether local grouping formed even at a relatively low density. Not only basic parameters such as linear and turning speeds, but also the multi-parameters covering instantaneous movement and dispersion patterns were recorded simultaneously across different micro-areas for resource supply and activity to comprehensively illustrate group behaviors. The parameters appeared in two patterns in the wild strain: one characterized by maximum speed and minimal separation of outliers from groups during the transition from light to darkness, and the other with many parameters showing local aggregation in the resource-supply (food and moisture) area before and after the maximum speed. Interestingly, all these parameters were significantly altered in a mutant strain, suggesting that genes contribute to local grouping behavior. In summary, our group behavior study contributes to unravelling the tendency of Drosophila to form groups, based on multi-parameter estimation observed across different micro-areas.

In the present study, groups of 10 adult males from wild-type strain Drosophila melanogaster Canton-S and corresponding mutant tab2201Y were continuously observed using automatic digitization. Data based on instantaneous movement and cumulated movement positions were obtained for micro-areas providing space for resources (food and moisture) and for activity (edge area and intermediate area [between edge and center-diffusion areas]) within the observation arena for 24 h. The results confirmed the natural tendency of local aggregation among individuals within the observation arena (14 cm × 14 cm) at a relatively low density of ten individuals. For Canton-S, temporal cooccurring patterns among different parameters were observed as time progressed, with two primary patterns identified in the resource supply areas: single peak and double peaks. The single peak was observed with maximum speed and I-index, indicating minimum degree of isolated individuals from groups, during the transition from the photoperiod to the scotoperiod. The double peaks occurred before (mid-to-late photoperiod) and after (end of scotoperiod) the single peak, co-occurring temporally with a number of parameters including duration rates, stop number (total occurrence of pauses), stop time (total duration of pauses), mean crowding (MC), and social space index (SSI), indicating local aggregations for feeding in accordance with maximum durations in resource supply areas. Temporally cooccurring trends in parameters were also found with the stop number and SSI in micro-areas associated with activity, indicating that short pauses were needed to keep balance between attraction and repulsion between nearby individuals. Overall, the measured parameters varied depending on the micro-area, light phase, and strain. In particular, behavioral differences were observed for tab2201Y, including an increase in speed, especially in the areas related to activity during the scotoperiod. Between strains, behavioral differences in the measured parameters were observed less for tab2201Y than Canton-S.