Many animals, including apex predators, move in groups. We know that this collective behavior is fundamental to animals’ ability to navigate complex environments, but little is known about what drives this behavior because so many factors influence its evolution. Scientists wonder, though, if all these animals share a basic drive such as mating, safety, or perhaps energy conservation.

“The key word is probably,” said Yang Fan Zhang, a postdoctoral researcher in Harvard’s Department of Organismic and Evolutionary Biology (OEB), because no one has measured it and compared it directly across animal groups. What is, mainly because it is difficult to have. A system that can measure not just a group, but the individuals in that group. But, we know that, evolutionarily, there is some pressure to improve the efficiency of energy use.”

In a new study published in eLifeZhang and co-author Professor George Lauder, also at the OEB and Curator of Ichthyology at the Museum of Comparative Zoology, questioned whether coordinated group movements by animals moving through a fluid could reduce the energy cost of locomotion. can. By combining biomechanics and bioenergetics (measuring the metabolic energy consumption and movement of animals simultaneously in a highly specialized experimental platform), the researchers found not only a remarkable amount of energy conservation, but also a significant amount of energy conservation per tail beat. Also indicated low energy consumption.

Land vertebrates evolved from fish, moving from fins to limbs and changing respiratory organs from aquatic to air breathing. Despite different environments and respiratory systems, all vertebrates and fish share the same metabolic pathways for energy production. One pathway uses oxygen called aerobic metabolism. The second pathway, called anaerobic, is used when oxygen is limited, or cannot provide enough energy to move at high speeds. Combined, they contribute to the total energy expenditure of movement. However, fish have a greater need to improve their mobility than animals that move in the air or on land. This is because water is 50 times more viscous than air and requires considerable energy to overcome fluid resistance during motion. Water also contains five times less oxygen per kilogram than air. That is, aquatic animals are “squeezed” by the lower limit of oxygen availability and are more stressed with energy demands.

To test the energy cost of movement in fish, Zhang and Louder designed a sealed water “treadmill” that controlled the speed of the water. By measuring the rate at which oxygen is expelled from the sealed “treadmill,” the researchers were able to differentiate the rate at which the animals took up oxygen.

“The system is designed so that the sensitivity of the measurement to capture the energetic cost of an individual fish is directly comparable to the cost of a group of eight fish,” Zhang said. “By standardizing fish biomass in a water treadmill with controlled water velocity, we can directly compare the cost of swimming between schools of fish and individual fish.”

The “treadmill” also features two high-speed orthogonal cameras to capture the unique characteristics of locomotion — one from the side, the other from below. This helped measure the three-dimensional positions of the fish and allowed the researchers to measure the distance between the fish in the school.

“What we discovered is that the total cost of moving for the group as a whole is much lower per biomass than for an individual, and the group expended the least amount of energy on average,” Zhang said. Velocity is one physical length per second.” . “When we look at studies that track animals in the wild, we find that many animals migrate at speeds of about one body length per second.”

The researchers found that moving fast required more energy, but so did moving slowly. However, at an average speed of one body length per second, they observed a decrease in energetic curves where swimming was at a minimum value, which increased at both fast and slow speeds, presenting a J-shaped relationship. went.

As the most diverse vertebrate group, fish species are of great cultural and commercial value to human society. Yet, a changing climate poses a direct challenge to fish biodiversity.

“Predictions of future fish species abundances cannot be based solely on the biology of individuals,” Lauder said. cause interactions between individuals within. Aquatic locomotion under environmental constraints provides insight not only into highly conserved features of vertebrate physiology, but also into the principles of fluid dynamics and the inner workings of animal locomotion.”

“I think what’s beautiful about this study is that we captured the full spectrum of energy costs in a comprehensive way that enabled us to quickly calculate energy costs,” Zhang said. Zhang said. “Scientists have been looking at this question for decades, but we found that the key lies in measuring not only aerobic, but also anaerobic expenditure. This is a huge part of any organism and, without measuring both, You only get half the story.