Wing coloration helps dragonflies withstand heat

Temperature is a key factor in determining where species can thrive and whether they are at risk from climate change. 

While much research has focused on how heat tolerance affects survival, less attention has been paid to how thermal traits influence reproduction, which is directly connected to extinction risk. 

Now, a team of researchers in the United States has explored whether male dragonflies with dark wing coloration, used as a sexual signal during mating, are more resistant to heat. 

Reproductive traits and heat tolerance 

The findings, published in the journal Frontiers in Ethology, provide new insights into the link between reproductive traits and heat tolerance.

“We show that dragonfly species that have evolved dark breeding coloration on their wings have also evolved the ability to tolerate high temperatures,” said lead author Noah Leith, a biologist at the University of Pittsburgh. 

“This finding paves the way for a whole new field of research exploring interactions between thermal traits and sexual signals.”

Wing coloration and mate selection

In many animals, including dragonflies, sexual signals like wing coloration play an important role in attracting mates, identifying species for reproduction, and deciding when to retreat from mating contests. However, these dark wing ornaments come with a downside. 

Dark colors absorb more heat, raising the dragonflies’ body temperature, which can result in physiological stress or cause males to abandon their reproductive territories.

“We see time and time again that animals will put their lives on the line to reproduce, even if it means encountering potentially lethal temperatures,” Leith said.

Wing coloration and heat stress

To investigate, the researchers analyzed 14 species of dragonflies living in tropical climates and five species from temperate regions. 

They discovered that species with dark, heat-absorbing wing coloration had evolved to withstand higher heat stress before reaching their critical thermal limits. 

“This enhanced ability to tolerate high body temperatures is likely crucial for shaping how dragonflies may respond to the changing climates of the future,” Leith explained.

Dark wings increase body temperature

The researchers found that dark wing ornaments can increase a dragonfly’s body temperature by 1°C to 2°C, which is approximately the same as the increase in thermal tolerance observed in species with dark wing patterns. 

The tropical species Tauriphila argo, also known as the arch-tipped glider, was found to have the highest heat tolerance among the species studied. 

This dragonfly has very dark wing patches near its core body, which absorbs more heat. Overall, the pattern of co-evolution between dark coloration and heat tolerance was even stronger in tropical species, where high temperatures are a constant challenge.

Evolution of heat tolerance 

Previous research has shown that rising global temperatures are causing some dragonfly species to evolve with less wing coloration. 

However, the new findings suggest that even if these species lose some of their coloration due to climate pressures, they will retain their ability to withstand hotter temperatures because they have already evolved this trait.

This study is one of the first to test whether thermal tolerance co-evolves with reproductive traits. 

“Our finding is particularly exciting because dark sexual coloration has evolved over and over across the tree of life and causes a wide variety of other animals to absorb extra heat too – from reptiles to lions and fruit flies,” Leith said. 

Surviving in a warming world 

This discovery highlights how evolutionary adaptations in response to reproductive needs may also help species survive in a warming world.

In the context of rapid global warming, being able to predict which species are vulnerable to extinction is crucial for preserving biodiversity. The researchers emphasize the importance of examining not just survival traits, but reproductive traits as well, to get a more comprehensive understanding of how animals respond to environmental changes. 

“Looking at vulnerability in only one aspect of animals’ lives is insufficient. We need a more nuanced understanding of how animals respond to changing environments as whole, complex organisms, in which their reproductive traits might influence their chances of surviving a heat wave, and vice versa,” Leith said.

Although the study analyzed 19 species, the researchers point out that there are thousands of dragonfly species worldwide. Future research could explore whether similar patterns exist across other species and types of animals. 

“It would be fantastic to someday test if heat tolerance co-evolves with sexual traits across life on Earth,” Leith concluded.

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