American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Unexpected non-genetic individual heterogeneity and trait covariance in Daphnia and its consequences for ecological and evolutionary dynamics”

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Clayton E. Cressler, Stefan Bengtson, and William A. Nelson

<i>Daphnia</i>.<br />(Credit: Nelson Lab: Shirley French)
(Credit: Nelson Lab: Shirley French)

If you look closely at any two animals of the same species, you will find differences. One may be larger than another, better at getting food, or better at finding mates. Many explanations exist for these differences. Two of the most common explanations are that the individuals differ because they have different genes or live in different environments. But what happens if those explanations vanish? Will there still be differences between individuals? If so, what does that mean for population dynamics and evolution?

In research now appearing in The American Naturalist, Clay Cressler, Stefan Bengtson, and William Nelson tackle these questions. By restricting the environmental differences experienced by the clonal freshwater crustacean Daphnia, they observe what happens to individual differences when their usual sources were removed. “Because these organisms are clones of each other, it gives us a great opportunity to look at where differences come from and what that means for their ecology and evolution,” says Dr. Cressler. Under carefully controlled environments, they find that non-genetic sources of variation contribute more than genetic sources to individual differences.

When these individual differences are scaled up to the population, they found that non-genetic sources of variation impacted population growth rates more than genetic sources. Surprisingly, independent of how traits co-varied among individuals, non-genetic sources of variation always slowed evolution in a way that is different from other evolutionary processes.

Clonal animals often show an abundance of genetic diversity within a population. Counterintuitively, these results show that high levels of variation among genetically identical individuals are an important mechanism maintaining these high levels of genetic diversity. Read the Article