How group behavior reduces energy costs in fish

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 to mate, protect, or perhaps conserve energy.

“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. There is a system that can measure not only a group, but the members of that group. 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 animal’s metabolic energy consumption and movement simultaneously in a highly specialized experimental platform), the researchers not only found a remarkable amount of energy conservation, but also Also indicated a reduction in energy consumption on pulse.

Land vertebrates evolved from fish, moving from fins to limbs and changing respiratory organs from aquatic to air breathing. Despite different environments and breathing systems, all vertebrates and fish are similar. Metabolic pathways to generate energy. 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. Meaning Aquatic animals The lower limit of oxygen availability is “squeezed” and the energy demand is greater.

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.”

“Treadmill” also used two high-speed orthogonal cameras to capture the unique characteristics of locomotion—one from a side view, 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 the group as a whole is much lower per biomass than an individual, and the group expended the least amount of energy at an average speed. Body length per second, Zhang said. “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, with increases at both fast and slow speeds that would suggest a J-shaped relationship. Is.

As the most diverse group of vertebrates, Fish species It has immense cultural and commercial value to human society. Yet, a changing climate poses a direct challenge to fish biodiversity.

“Predictions about the future abundance of fish species cannot be based solely on the biology of individuals,” Lauder said. cause.”

“Studies of the energetics of aquatic locomotion under environmental constraints provide 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.”