Many animals ranging from swarming insects to wildebeests form large, orderly groups. This collective behavior is often crucial to survival. It may help animals find food, escape predators, enhance the way they sense their surroundings and augment their decision making. But the processes that enable these group gatherings are not well understood.

It can be difficult to study large animal groups in the wild, but studying smaller animals in the laboratory can help scientists tease apart the processes that drive animal clustering step by step. For this work, researchers of Dr. ZHU Yan's group from the Institute of Biophysics (IBP) of the Chinese Academy of Sciences in China looked at what drives clustering in the sociable fruit fly Drosophila melanogaster. Results were published online in eLife on Jan. 21, 2020 in an article entitled 'Emergence of social cluster by collective pairwise encounters in Drosophila'.

Figure. Self-organized aggregation, encounter response and regulation of ppk neurons in Drosophila.
(The image by Dr. ZHU Yan's lab)

"Analysing the aggregation process in fruit flies would help us understand how individuals interact to form a social group and what senses are used during this process," says lead author JIANG Lifen, a PhD student at the School of Life Sciences, University of Science and Technology of China, Hefei. "Looking at this process in fruit flies may give us some insight into more complex collective behaviours in other animals."

In addition, Jiang and the team discovered that fruit flies placed in shallow, covered dishes spontaneously form clusters with regular spacing between flies. By observing the flies, the scientists learned that these formations are driven by fly-fly interactions in which the flies use their legs and wings to touch each other and then establish some personal space. But when the team systematically interfered with their senses, including sight, odour and touch, this stopped the flies from forming these neat clusters. "Depriving fruit flies of their senses resulted in abnormal responses to encountering another fly and a high failure rate of cluster formation," Jiang explains.

The researchers then showed that the flies' physical interactions with each other switch on their sensory nerve cells. Without these cells, they are unable to establish the usual socially acceptable distances between themselves and other flies that are necessary to form organised clusters.

"Our findings suggest that self-organisation in flies might rely on just a few simple rules," says senior author ZHU Yan, PhD, Professor at the Institute of Biophysics, Chinese Academy of Sciences, Beijing. "More studies are now needed to determine whether similar rules govern gatherings in larger animals."

The web link for this paper is https://doi.org/10.7554/eLife.51921.  

Contact: ZHU Yan
Institute of Biophysics, Chinese Academy of Sciences
Beijing 100101, China
Phone: 86-10-6488540
Email: zhuyan@ibp.ac.cn

(Reported by Dr. ZHU Yan's group)