Tropical fish from Okinawan sea on display in a glass tank in Tokyo. (AP)
New Delhi, Aug. 16: By coaxing fish to play a video game, scientists may have resolved a century-old mystery, untangling the biological roots of the superbly coordinated, synchronised movements displayed by many animals, birds and fish.
Bangalore physicist Vishwesha Guttal and collaborators in the US and the UK have produced the first experimental evidence for the idea that synchronised movements by members of a herd, flock or a school reduce their risk of being eaten by predators.
Dozens of species — from wildebeest in the African Serengeti to pigeons in Indian skies to sardines in the world’s oceans — show coordinated movements whether travelling in groups or trying to escape predators.
Biologists have long suspected that living in groups reduces the risk of predation, but the evolutionary roots of the fine synchronised twists and turns each member of a group executes during the collective movement have remained a mystery.
In the new study, evolutionary biologist Iain Couzin at Princeton University, Christos Ioannou at Bristol University and Guttal designed an experiment in which predatory bluegill sunfish, denied food for 24 hours, were shown simulated prey on a screen.
The hungry sunfish released at one end of a fish tank swam towards the other where a screen displayed virtual prey — dots of light made to look and move like tiny worms and crustaceans.
In the real world, it is near-impossible to manipulate prey behaviour, said Couzin. This is a substantial problem that had hampered previous research into how predators may influence the evolution of prey behaviour, Couzin told The Telegraph.
The use of the virtual prey allowed scientists to control each individual’s behaviour — some dots were programmed to move in perfect alignment with the group’s collective behaviour, some would deviate only slightly while others would show larger deviations.
“The real fish happily attacked the virtual prey,” said Guttal, now an assistant professor at the Indian Institute of Science, Bangalore.
The scientists observed each fish’s first target prey, and stopped the experiment after the fish had touched a dot on the screen to avoid the fish’s memory from influencing future results.
Their study, to be published today in the US journal Science, found that the fish targeted prey that were typically members of a small group. “We also observed that prey with a tendency to align their direction of motion with neighbours quickly were at less risk of being eaten,” Guttal said.
Scientists have speculated about the biological advantages of group behaviour in animals and birds for over a century.
In 1905, Edmund Selous, a British ornithologist, observed a remarkable synchrony of movement among birds called starlings. While many scientists have since then analysed the costs and benefits of group size and position within the group, how the risk of predation changes with the response to individuals had remained unknown — until now.
“This new study uses a neat trick to test something that has not been explored before,” said Sriram Ramaswamy, a physicist at the Tata Institute of Fundamental Research Centre for Interdisciplinary Sciences, Hyderabad. Ramaswamy was not connected with the experiments but himself specialises in theoretical work on the collective movement of living organisms.
Evolutionary biologists have speculated for decades that living in groups is helpful because it allows the spotting of predators early and from a distance, a process some call the “many eyes effect”. Predators, scientists say, are also likely to experience confusion when having to choose from many possible targets.
“There are lots of mathematical models to represent collective behaviour, but this study is important because it creates a set-up in which the behaviour of virtual prey can be controlled experimentally to see how a real predator interacts with them,” Ramaswamy said.
“It’s an example of how you can quantitatively study social behaviour,” said Ramaswamy, who is on leave from the IISc.
Couzin said studying the evolution of coordinated behaviour is expected to lead to a better understanding of the evolution of cooperation and other more sophisticated interactions among organisms.
“The transition from individual to group living is one of the major evolutionary transitions,” he said. “How coordinated action emerges from simple rules may hold the key to understanding how more advanced social organisation has emerged over time.”