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Evolution is actually pretty predictable

PRINCETON (US) — “Is evolution predictable? To a surprising extent the answer is ‘yes’,” says Princeton professor Peter Andolfatto.

New research by Andolfatto and colleagues published in the journal Science suggests that knowledge of a species’ genes—and how certain external conditions affect the proteins encoded by those genes—could be used to determine a predictable evolutionary pattern driven by outside factors.




Though separated by 300 million years of evolution, these diverse insects—which include beetles, butterflies, and aphids—experienced changes to a key protein called sodium-potassium adenosine triphosphatase, or the sodium-potassium pump, which regulates a cell’s crucial sodium-to-potassium ratio.


Jianzhi Zhang, a University of Michigan professor of ecology and evolutionary biology, says that the new study shows that certain traits have a limited number of molecular mechanisms, and that numerous, distinct species can share the few mechanisms there are.


“The finding of parallel evolution in not two, but numerous herbivorous insects increases the significance of the study because such frequent parallelism is extremely unlikely to have happened simply by chance,” continues Zhang, who is familiar with the study but had no role in it.



33 mutations



Cardenolides disrupt the exchange of potassium and sodium, essentially shutting down the protein, says Andolfatto, an assistant professor in Princeton’s Department of Ecology and Evolutionary Biology and the Lewis-Sigler Institute for Integrative Genomics.


The researchers sequenced the expression of the sodium-potassium pump protein in insect species spanning three orders: butterflies and moths (Lepidoptera); beetles and weevils (Coleoptera); and aphids, bed bugs, milkweed bugs, and other sucking insects (Hemiptera).




Significantly, the researchers found that multiple gene duplications occurred in the ancestors of several of the resistant species. These insects essentially wound up with one conventional sodium-potassium pump protein and one “experimental” version, Andolfatto notes.


“These gene duplications are an elegant solution to the problem of adapting to environmental changes,” Andolfatto says. “In species with these duplicates, the organism is free to experiment with one copy while keeping the other constant, avoiding the risk that the new version of the protein will not perform its primary job as well.”

Protein evolution

The researchers’ findings unify the generally separate ideas of what predominately drives genetic evolution: protein evolution, the evolution of the elements that control protein expression or gene duplication.

This study shows that all three mechanisms can be used to solve the same evolutionary problem, according to Andolfatto.


“Historically, studying genetic evolution at this level has been conducted on just a handful of ‘model’ organisms such as fruit flies,” Andolfatto says. “Modern sequencing methods allowed us to approach evolutionary questions in a different way and come up with more comprehensive answers than had we examined one trait in any one organism.

“The power of what we’ve done is to survey diverse organisms facing a similar problem and find striking evidence for a limited number of possible solutions,” he suggests. “The fact that many of these solutions are used over and over again by completely unrelated species suggests that the evolutionary path is repeatable and predictable.”

The Centre for Genetic Engineering and Biotechnology, the National Science Foundation, and the National Institutes of Health supported the work.

Andolfatto worked with lead author and postdoctoral research associate Ying Zhen, and graduate students Matthew Aardema and Molly Schumer, all from Princeton’s ecology and evolutionary biology department, as well as Edgar Medina, a biological sciences graduate student at the University of the Andes in Colombia.

Source: Princeton University

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