Plants evolve away from useless defenses, study reports

Avatar By Joseph Scalise | 2 years ago

A group of scientists at the Drexel University have found that plants will stop using defense methods that do not work, instead evolving new traits as a way to better protect themselves in the future.

In the study, the team found this by analyzing different types of flowering plants known as dogbanes and milkweeds. Both species are connected in that they each use a highly toxic chemical substance — known as pyrrolizidine alkaloids — as a defensive measure against would-be predators.

The team traced the plants back to when they first began to produce the chemical and found that they stopped creating it at four different periods throughout their existence. The reason? Danainae butterflies.

Unlike mammals, the insects are not harmed by toxic alkaloids. As a result, the plants stopped producing the chemicals as soon as they became ineffective. In fact, certain milkweeds made the change as soon as the butterflies began to actively seek out the plants.

“Pyrrolizidine alkaloids are likely an ineffective defense against Danainae,” explained study leader Tatyana Livshultz, a researcher at Drexel University, according to International Business Times UK. “Furthermore, they are actually beneficial to them since they take in these chemicals for their own defense against their predators.”

This study is important because it actively supports the “defense de-escalation” hypothesis, which states that organisms will stop using defenses that no longer work. This is a prime example, and it could help scientists get a better idea of the basics behind co-evolution.

“Apocynaceae (milkweed) species of this lineage produce a number of different classes of defensive chemicals, including cardenolides and other types of alkaloids,” added Livshultz. “It has been shown that cardenolides are at least partially effective defenses against adapted herbivores, such as the monarch butterfly, the most familiar species of Danainae to Americans.”

Though researchers are not sure why some milkweeds still produce the deadly chemicals, they postulate that it could be because they want to deter other insect types that are still deterred by the toxins.

New Phytologist.