Novel survival tactic discovered in butterflies

Agência FAPESP/DICYT A new survival tactic has been discovered in butterflies, according to a paper published in the journal Neotropical Entomology. The lead authors are Carlos Eduardo Guimarães Pinheiro, a researcher at the University of Brasília (UnB), and André Lucci Freitas, affiliated with the University of Campinas (UNICAMP) in São Paulo State, Brazil.

The study, in which researchers from the University of New Orleans also took part, as well as a colleague of Pinheiro’s at UnB, was supported by FAPESP under the auspices of its BIOTA Program.

During their evolution, several butterfly species are known to have developed traits such as the ability to release toxins, resulting in an “unpleasant” taste to scare off birds and other predators. These unpalatable insects also advertise their toxicity by displaying bright colors, as if to warn enemies to stay away.

Palatable butterflies have also developed survival tactics under pressure from predation. For example, they are faster. Many also sport multicolored wing patterns that identify them as nimble and hard to capture.

Slower palatable butterflies should naturally be priority targets for predators, but they, too, use tricks to survive: one such ploy is “escape mimicry”, which involves imitating the colors of their unpalatable cousins.

In summary, unpalatable butterflies do not need to invest in escape tactics. They are poisonous and can afford to fly more slowly. Palatable butterflies need to be fast and nimble, or alternatively to mimic unpalatable species, to avoid being eaten. However, the new study shows this is not always what happens.

Pinheiro, Freitas and colleagues focused on two species in particular: Heraclides anchisiades capys, which is palatable and very nimble, and Parides anchises nephalion, which is unpalatable, slow and highly poisonous.

These two species are not close relatives, yet they display very similar colors, despite some differences. The wing patterns of the nimble H. anchisiades closely resemble those of the poisonous P. anchises, an inhabitant of tropical regions in the Americas.

Many other species apart from H. anchisiades “imitate” P. anchises in a classic example of mimicry, whereby a palatable creature looks very much like an unpalatable one and benefits from the resemblance. However, among all the species that mimic P. anchises, H. anchisiades is one of the fastest and also the most widely distributed in the Americas.

At first glance, H. anchisiades looks as if it must be highly toxic, given its coloring. It has the best of both worlds as far as defending itself against predators is concerned. A bird that ignores the poisonous pattern and attempts to prey on H. anchisiades will find itself pursuing a nimble butterfly and will probably expend a great deal of energy without obtaining food. By using mimicry to trick its pursuers, this butterfly reduces the probability of being eaten to a minimum and is able to concentrate on activities such as foraging and reproducing.

“The nimble butterfly mimics the poisonous butterfly, gaining adaptive advantages by associating its speed and agility with a trait known by birds to signify unpalatability, i.e., toxicity,” Freitas said.

P. anchises, commonly known as the Anchises Cattleheart, is one of the most poisonous butterflies in the tropical Americas. It flies slowly, thereby suggesting that avoiding predators is not a priority. Nevertheless, its coloration resembles that of the agile H. anchisiades.

Given that the poisonous butterfly lives in the tropics and the speedy butterfly is found throughout the Americas, it seems likely that the ancestors of the fast palatable H. anchisiades mimicked the unpalatable P. anchises, thereby gaining an adaptive advantage that enabled the species to extend its habitat to the entire continent.

The more limited geographic distribution of P. anchises appears to suggest a second possibility. “A highly poisonous butterfly would also mimic an athletic, widely distributed butterfly to minimize the chances of predation,” Freitas said. It is this possibility that the study brings to light.

The suggestion that an unpalatable species may mimic a palatable species as a survival tactic to gain adaptive advantages is not an idea that can be found in any biology textbook. On the contrary, it is a distinctly original hypothesis.

“The traditional view is that escape mimicry is found only in palatable species. Our research suggests that in several cases an unpalatable species may use escape mimicry. This would change the theory of mimicry and make it more complex,” Freitas said.

Dual strategy

The study promises to spark discussion among specialists, owing to a number of findings, according to Pinheiro. “I’d say the key contributions of our research are the finding that butterfly coloration doesn’t relate just to palatability, but is associated by predators with difficulty of capture, and that palatable butterflies may converge in terms of coloration to form types of mimicry based on the ability to escape,” he said.

“In addition, even some unpalatable butterflies may also be fast fliers and use both strategies to avoid attack by birds. The study raises a number of novel hypotheses for testing in future research.”

The article “Both Palatable and Unpalatable Butterflies Use Bright Colors to Signal Difficulty of Capture to Predators” (doi: 10.1007/s13744-015-0359-5) by Pinheiro, Freitas et al., published in Neotropical Entomology, can be read at link.springer.com/article/10.1007%2Fs13744-015-0359-5.