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Natural Selection Seems To Favor Slower Snails

May 11, 2009

Everything is coming up roses for snails with slower metabolic rates, Chilean researchers have found.

This is the first instance that natural selection has chosen this trait in any kind of species.  These snails have a leg up over others because they reserve more energy for other actions like growth or mating, says the findings, available in the journal Evolution.

Roberto Nespolo and Paulina Artacho from the Southern University of Chile reviewed an old hypothesis called the “energetic definition of fitness”.

“This predicts that animals that spend less energy will have more surplus for survival and reproduction,” stated Nespolo.

Hardly any studies have tested the concept, and three prior tests on rodents came up empty. “Ours is the fourth and the first to demonstrate significant directional selection on metabolism,” says Nespolo.

Nespolo and Artacho recorded the size of 100 garden snails. They noted their standard metabolic rate, or SMR, by calculating the amount of carbon dioxide each animal emitted while resting.

“Standard metabolic rate is the energy required for maintenance. In other words, having less maintenance permits you to have more energy for other activities, such as growth and reproduction. That’s why less metabolism represents higher fitness,” Nespolo said.

Following seven months, they recalled the snails back to the lab, including the empty shells of those who perished. The snails that lived had a 20% slower SMR rate than those who died.

The results found that the slower the metabolic rate, the better the probability is of survival. That means natural selection is picking snails that are better at conserving energy, noted Nespolo.

The researchers were wise in choosing the garden snail to study. By watching the snails housed in purpose-constructed houses, Nespolo and Artacho avoided the problem of their subjects running away, and also had empty shells to study when they died.

“We could recover the dead because of their shells and because they did not move more than a couple of meters each year,” says Nespolo.

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