Butterflies must gamble on unpredictable futures

Even butterflies need to make decisions about adapting to a changing and unpredictable future, research shows.

A team led by Darrell Kemp of Macquarie University found that, for butterflies, there may be no single strategy when it comes to adapting to a changing environment. Instead, some butterflies play it safe, and others take risks.

Fast facts: Grass yellow butterflies

  • Eurema hecabe is a pierid butterfly with yellow wings
  • They are found around Asia, Africa and Australia
  • The butterfly exhibits seasonal polyphenism – it changes colour based on seasons
  • It is darker in summer and paler after the monsoon

Grass yellow butterflies (Eurema hecabe) are known for leaving lots of larvae on plants that have been overeaten, which forces the larvae to make choices on how to adapt to unpredictable futures.

The paper, published in Evolution, shows that grass yellow butterflies choose between prematurely maturing or delaying maturation and staying as a larva for longer; the best choice depends on what the future (ie. amount of rainfall) will be like, although this is impossible to predict.

Similarly, they showed that the choices on how to overcome potential food scarcity were varied. Some individuals became pupae early, which meant they would become adults faster and be able to fly away from the plants that had little foliage left. The trade-off was that they had to endure being a small adult.

Other larvae decided to endure the food scarcity and become an adult later. This would make them larger and stronger in adulthood, but at greater risk of dying before reaching adulthood.

“This finding points to evolutionary bet-hedging,” says Kemp. “Unpredictability of the natural environment means that, similar to rock-paper-scissors, no single developmental strategy can ultimately come to dominate across the population.”

Interestingly, the choices also appeared to be somewhat related to genetic lineage. This means that the butterflies’ predisposition to a certain risk choice is based partially on genetics.

“It’s an intriguing proof of concept for how an unforeseeable future may foster the coexistence of diverse evolutionary solutions,” says Kemp.

“Species that naturally face such uncertainty should be better equipped to handle variation in the climate if – as in Eurema butterflies – the ability to do so already resides within their gene pool.”

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