“Energetic Definition of Fitness” and Slower Snails

Traditional definitions of Darwinian fitness emphasize reproductive design and adaptability to environment. The “energetic definition of fitness” emphasizes the distribution of energy among the following activities: food acquisition, metabolism, growth, reproduction, and survival.

Coinciding with the energetic definition of fitness, it appears that evolution is actually slowing snails down, leaving them more energy for other tasks. A BBC News article noted, “It is the first time that evolution has been shown to select for [lower metabolism] in individuals of any species.” Why would nature select for such a trait? According to evolutionary biologist Roberto Nespolo, “Animals that spend less energy [on maintenance] will have more surplus for survival and reproduction.”

Nespolo is currently conducting studies on this topic, and has found “significant directional selection on metabolism.” His team measured standard metabolic rate – the “minimal amount of energy an animal requires to stay alive” – by gauging the amount of carbon dioxide produced by each snail at rest. In a sample of 100 snails, Nespolo found that after seven months, the surviving snails had a 20% lower metabolic rate than those who failed to survive.

Even still, Nespolo’s team must now answer the question: “is having a slow metabolism linked to moving slowly?” The relationship between these two variables is critical to understanding what’s being selected for and snail energetics.

-Alyssa Martin