Evolutionary processes occur in patterns, according to Princeton research team

The team studied 29 different species of insects, 14 of which had developed a resistance to cardenolides, a class of toxins. The researchers found that these insects used similar methods of resisting the toxin, even though the different species were spread out over 300 million years of evolution.

“You have very distantly related insects completely independently coming up with solutions that look very, very similar,” senior researcher and ecology and evolutionary biology professor Peter Andolfatto said, “sometimes involving the very same change to DNA.”

Andolfatto worked with postdoctoral research associate Ying Zhen, ecology and evolutionary biology graduate students Matthew Aardema and Molly Schumer, and Edgar Medina, a biological sciences graduate student at the University of the Andes in Colombia, on the study.

All of the toxin-resistant insects studied had changes in a protein called the sodium-potassium pump, which is used to balance a cell’s sodium-to-potassium ratio. The evolved protein allows the insects to feed on plants, such as milkweed and dogbane, that use the toxin cardenolides as a natural defense.

There were many other possible genetic developments that would have led to the same sort of immunity, Andolfatto said, but the insects independently used the same evolutionary method to adapt to the toxin. This consistency suggested that evolution ends up following a path that works to minimize the emergence of negative side effects from beneficial mutations.

“We hypothesize that the reason we see so much of the same solution being used over and over again is that there is only a limited number of solutions that actually minimize these bad effects,” Andolfatto said. “So you’re going to choose those ones.”

The results of the study will go a long way toward demonstrating there are factors that limit the process of evolution at a molecular level, Andolfatto said, adding that this knowledge should allow for a stronger handle on the understanding of evolutionary paths.

“Is there any limit whatsoever to adapting to the natural world, or is it an anything goes-type situation?” Andolfatto said. “I think our study really nicely illustrates that it’s not true that anything goes.”

The team was also one of the first to use a set of “next-generation” sequencing tools, Andolfatto said. Previous researchers, when studying genetic evolution, had only looked at a specific set of “model” organisms such as fruit flies for their studies.

“Usually, for this kind of study, people just do [a polymerase chain reaction],” Zhen said. “They target one gene, and then they design specific primers and they try to get the single gene out.”

By using the new sequencing tools, the team went beyond previous levels of investigation and actually sequenced and assembled the genes in question for all 29 species they wanted to study, resulting in a large sample of organisms examined for a single trait.