The fruit fly may not seem like a very social animal. Yet, this tiny insect has led to the discovery of a new phenomenon - a social safety cue.
From schools of fish to herds of antelope and even human societies, one of the many advantages of living in a group is its inherent safety. Surrounded by their peers, individuals can lower their vigilance and calmly engage in other activities, such as searching for food or watching YouTube videos.
But the Safety in Numbers rule has more to it than just being together. In many cases, communication also plays a big role. We are all familiar with ways animals signal danger to each other - barks, yelps, and shrieks immediately come to mind. But how do they communicate that the threat has passed? And how is this information processed in the brains of others?
Scientists at the Behavioural Neuroscience lab are interested in answering these questions. Recently, the team demonstrated that individual fruit flies don't only flee when threatened. If a menacing shadow appears, but escape is impossible, single flies respond in the same way any one of us would: they freeze.
This finding triggered the researchers' curiosity, would this behaviour change if other flies were around?
As a first step to answering this question, the team systematically characterised the effect of group size on freezing. Their results showed that social context mattered - when in company, flies always spent less time freezing than when alone!
But why were they freezing less? Were they simply feeling safer in the presence of other potential victims? Or was there a hidden communication at play?
The team tested the "communication hypothesis" by performing further experiments. Now, instead of using groups of normal flies, they created new types of groups. These consisted of one normal fly and four "special" companions, which were either blind flies or magnetic "dummy" flies. This approach allowed the researchers to artificially create new patterns of group behaviour and assess their effect on the normal fly.
Their results revealed that the flies were indeed attentive to the behaviour of their peers. An individual fly was less likely to freeze in response to the threat if its companions were moving. And even if it froze, it would begin moving earlier if others were buzzing around.
In other words, flies were interpreting the movement of others as a social cue of safety!
Now that the researchers uncovered this new social cue, they turned their focus to the brain.
Their first suspect was a set of visual neurons that are known to respond to the movement of small objects.
The team shut down the activity of these neurons and observed whether the flies' behaviour changed. The manipulation had a clear effect. The flies still froze when the threat appeared, but they were much worse at using the movement of their peers as a safety cue.
These findings are very exciting - although there is ample evidence of social buffering of fear in the wild and the lab, until now, the cues mediating this phenomenon were unknown. Moreover, the researchers believe that the parallels between flies and other animals may pave the way for understanding common mechanisms across species.
The team is exploring further how the brain detects and processes this new social cue. Their end goal is to identify the full neural-circuitry involved in the social communication of safety.