For more than a hundred years, scientists have used a theory to describe how an animal's surface area and volume change with body size. Now, researchers from James Cook University (JCU) and the University of Massachusetts have confirmed this theory in sharks, using advanced 3D modeling techniques to study one of the ocean's most iconic predators.

"We found that sharks follow what's called the 'law of two-thirds scaling' almost perfectly," said Joel Gayford, a PhD student at James Cook University and lead author of the study. "This law helps explain how animals exchange heat, energy and oxygen with their environment - so it was significant to confirm this in normal animals, not just cells."

The team worked with computer graphics artist Johnson Martin to develop high-resolution 3D scanning technology to create detailed digital models of 54 shark species.

These scans provide researchers with precise measurements of surface area and volume, providing valuable insights into how body shape affects physiology.

"This ratio is crucial," said Dr. Jody Rumer, professor of marine biology at James Cook University and co-author of the study. "It is fundamental for animals to breathe, regulate body temperature and process waste. Now, for the first time, we have shown that it works in an animal as complex and diverse as a shark."

To rigorously test this rule, the team used phylogenetic regression analysis—a statistical method that takes into account evolutionary relationships—and found that shark body surface area is proportional to volume raised to the power of 0.64. This is only 3% lower than the theoretical prediction of 0.67.

Cutting-edge 3D modeling technology has confirmed that sharks follow the "law of two-thirds scaling" almost perfectly. Image source: James Cook University

"It's incredible," Rumer said. "This suggests that sharks evolved this ratio, perhaps because it was too costly to deviate from it, or because they were constrained by early development."

In fact, the team believes that evolutionary and developmental constraints could explain why sharks from vastly different habitats and lifestyles still follow the same scaling rules.

"Changing how tissue is distributed in the body may require significant changes during early embryonic development - which is expensive from an energy perspective," Gayford said.

Importantly, these findings have real-world applications. "The ratio of surface area to volume is a key input in equations used to model how animals respond to climate change, such as how quickly they regulate their body temperature or how efficiently they use oxygen. Now, we can apply these equations to sharks and other large animals with more confidence."

This study highlights how modern imaging technology - and some very patient digital modeling - can answer ancient biological questions.

Compiled from /scitechdaily