Researchers have discovered a brain molecule which works as a 'thermometer' for the presence of others in an animal's environment. Zebrafish 'feel' the presence of others via 'mechanosensation' and water movements, which turns the brain hormone ON.
Varying social conditions can cause long-lasting changes in animal behaviour. Social isolation, for instance, can have devastating effects on humans and other animals, including zebrafish. The brain systems that sense the social environment, however, are not well understood.
Fish perceive movement ("mechano-sense") in their immediate vicinity via a sensory organ called the lateral line. To test the role of mechanosensation in driving pth2 expression, the team ablated the mechanosensitive cells within the fish's lateral line. In previously isolated animals, the ablation of the lateral line cells prevented the rescue of the neuro-hormone that was usually induced by the presence of other fish.
Just as we humans are sensitive to touch, zebrafish appear to be specifically tuned to swimming motion of other fish. Researchers observed changes in pth2 levels caused by water movements that are triggered by conspecifics in the tank.
A relatively unexplored neuropeptide, Pth2, tracks and responds to the population density of an animal's social environment.