Male Dragonflies Get Less Flashy in Hotter Climates

When temperatures rise, male dragonflies have come up with a decidedly drab but clever way to stay cool. They lose some of the showy pigmentation on their wings, a new study finds. Shedding the dark patches helps regulate their body temperature, but it could make it harder to attract mates and fend off rivals.

Male dragonflies typically have dark wing patterns that entice female mates while frightening potential competitors. 

“Only the best-conditioned males are able to produce really large patches of pigmentation, so their rivals seem to know that they'll lose if they challenge a male with large patches, and females seem to prefer males with large patches,” Michael Moore, a postdoctoral fellow with the Living Earth Collaborative at Washington University in St. Louis, who led the study, tells Treehugger.

But that dark pigmentation can heat up an insect’s body, just like wearing dark clothes on a hot, sunny day. Having a lot of dark wing pigmentation can heat dragonflies up by as much as 2 degrees Celsius (roughly 3.5 degrees Fahrenheit).

“The dark pigmentation on the wings seems to absorb solar radiation, and that energy gets converted into heat. So males with larger patches heat up more than males with smaller patches or males with no patches at all,” Moore says.

“Under cool conditions, this extra heating appears to provide modest benefits to a male's ability to fly. Under warm conditions, however, this extra heating can be quite detrimental—potentially damaging wing tissue, causing male body temperatures to overheat, and plausibly even killing males.”

Wings and Weather

For the study, published in the journal Proceedings of the National Academy of Sciences, researchers created a database of 319 dragonfly species using observations from citizen scientists on the platform iNaturalist.

First, they looked to see whether dragonflies have adapted to warmer climates with evolutionary changes in wing coloration. They found that species that have ranges that are warmer have males that evolved with less coloration on their wings.

“This component of the study also revealed that, within a given species, populations that have adapted to warmer parts of the species' range have evolved less male wing coloration than populations of the same species that have adapted to cooler parts of the geographic range,” Moore says.

“Showing that species and populations within species exhibit similar responses to the same environmental factor provides strong evidence that the evolution of less male wing coloration is a really consistent way that dragonflies adapt to warmer climates. This got us wondering about whether dragonflies might also shift their wing coloration as the planet's climate continues to warm.” 

So then they used nearly 3,000 citizen-scientist observations from 10 species of dragonflies and measured the amount of wing coloration and the year in which each insect was observed. They matched up those observations to the yearly temperatures for North America and found that from 2005 to 2019, male dragonflies that were spotted in warmer years had less coloration on their wings than those of the same species that were observed in cooler years.

They discovered natural selection has prevented highly ornamented male dragonflies from breeding in warmer years, compared to cooler years.

Based on their measurements, the researchers forecast male dragonflies should lose a moderate amount of wing pigmentation over the next 50 years in order to adapt to rising global temperatures.

While male dragonflies are sacrificing their flashiness to keep cool, females aren’t making the same changes.

“In most cases, female wing pigmentation shows no response to climatic temperatures. And in some really interesting cases, the wing pigmentation of females responds to the climate in exactly the opposite way than the wing pigmentation of males of the same species!” Moore says.

“We don't yet know what exactly shapes the evolution of female wing pigmentation in these dragonflies. However, what these results do indicate is that one sex might respond pretty differently to the climate than the other(s). A lot of research on how plants and animals will respond to global climate change assumes that the sexes will react in similar ways, and our research really demonstrates that that might not be a great assumption.”

Having different amounts of pigment on their wings helps males and females of the same species identify each other. If male wing pigmentation adapts due to warming temperatures and female wing pigmentation evolves for another reason, females may no longer be able to recognize males of their own species, which could cause them to mate with males of a different species.

"Rapid changes in mating-related traits might hinder a species' ability to identify the correct mate," Moore says. "Even though our research suggests these changes in pigmentation seem likely to happen as the world warms, the consequences are something we still really don't know all that much about yet."