A team of scientists has discovered that fish form closer bonds and make new friends when there’s a risk of predation. If guppies think a predator is in the area, they develop stronger friendships, especially if their social group is small. The findings are in a paper that was just published in the journal Scientific Reports.
Trinidadian guppies (Poecilia reticulata) are tropical fish that are popular among aquarium owners because of their colorful patterns and ease of care. Although social, they don’t school but instead form small, loose-knit groups called shoals. Previous research has showed that guppies can form and maintain long-term friendships, sometimes following their buddy to a new shoal.
Researchers from the University of Exeter collaborated with the University of York and the University of the West Indies to study guppy social networks. The team caught 420 wild female guppies from the Aripo River in Trinidad and moved them to aquariums after allowing them to acclimate to the new water conditions. The team only used female guppies in their study because male guppies don’t form the same long-lasting bonds as females and instead move from shoal to shoal regularly. The guppies were split into two groups, a predation group and a control group. In the predation group, a mechanical “predator” was introduced to the aquarium while the control group didn’t experience any predation scenarios. The researchers observed the behavior of the fish and recorded signs of “friendships” such as time spent together.
The research team found that guppies in the predation group were much quicker to form friendships with fish they hadn’t previously interacted with. They also formed stronger bonds, sticking together even as they moved between small shoals. The effect was greatest when groups were smaller; the authors point out that this is because it’s easier to recognize individuals in a small shoal. These friendships continued even after the risk of predation was gone.
The team’s findings show that guppies form stronger friendships when exposed to danger. This was the first recorded case of the phenomenon in a fish species. The authors believe that their study provides more evidence for the theory that friendships originally evolved as a response to predation and other dangers.
Heathcote et al. Fear of predation drives stable and differentiated social relationships in guppies. Scientific Reports (2017).