Of mice and elephants, Monash scientists shed new insights into physiological evolution

a mice and an elephant

It is a question that scientists have been trying to resolve for centuries, but might it be due to evolutionary chance?

Photo credit: Source, Elephantfacts.net

Why is it that a 4000kg elephant needs significantly less food than 4000kgs of mice?

You might think that based on the mass of each they would require the same amount of food.

But in fact that elephant requires less than 10 per cent of the amount of food required to feed 4000kg of mice.

The answer to the discrepancy lies in metabolic allometry, or the study of the relationship between body size and metabolism.

Now a team of researchers led by Monash scientists has ruled out that the discrepancy is the result of chance in a study published today in Nature Ecology & Evolution.

“For reasons unknown, a 4000 kg elephant will use a lot less energy (less than 10%) than 4000 kg of mice (that's about 133,000 mice),” said lead study author Professor Craig White, from the Monash School of Biological Sciences.

“Each gram of elephant has a metabolic rate that is much, much lower than each gram of mouse,” he said.

“This pattern has been known since the early 1900s, and is known as allometric scaling.

“Our study looked at whether the pattern might arise through chance alone, because genes that affect metabolic rate also affect size.”

To test this, the research team, which included PhD and honours students, postdocs, and collaborators at Monash, University of Queensland, and around the world - measured the metabolic rates of thousands of animals including insects, fish, reptiles, amphibians, birds and mammals.

They combined this information with data for thousands of other species from the literature.

“We then used these data to simulate evolution across the animal tree of life,” said Professor White.

“And through that process we’ve been able to eliminate the possibility that the pattern arises through chance.”

Professor White said there must be a reason, and it could be because of some kind of physical constraint.

“Large animals might have difficulty dissipating heat or distributing resources,” he said.

“Or it could be because natural selection favours lower metabolic rates in larger animals and higher metabolic rates in smaller animals for some other reason.”

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