Imagine two fates — having a significant other but roasting, or staying cool but having no chance at attracting a mate. Such is the unenviable situation facing male dragonflies.
In a study published last week, local researchers have discovered that male dragonflies have less wing coloration in warmer climates, an adaptation that prevents them from overheating in the sun. This finding furthers scientists’ understanding of how organisms respond to climate change ― and how to conserve them.
The adaptation is a tradeoff: Female dragonflies use the markings to identify mates, so dragonfly reproduction could be affected as they disappear. Females might even have difficulty telling if a male is her own species.
It’s important to know if organisms can adapt to a changing climate fast enough and how this affects their ability to reproduce. In fact, a longstanding question in biology is how organisms adapt to living in different climates.
“Given the ongoing climate crisis, answering this question is as important as it’s ever been,” said Michael Moore, a postdoctoral researcher at Washington University and lead author of this study.
The team of Washington U. and St. Louis University researchers compared records of wing ornaments, or markings, on 319 species of dragonflies. They found that dragonfly species in warmer climates had less wing ornamentation than species that live in cooler climates.
They also looked at the wings of 10 broadly distributed species to see if wing markings varied in different populations of the same species. To do this, they measured the wings of over 2,700 dragonfly photos on iNaturalist, a community science website where people upload photos of plants and animals.
The result? Even within the same species, males in warm climate populations had less markings than those in cooler regions.
Moore’s previous research has shown that heat from the sun can increase dragonfly wing temperatures by about 3.5 degrees Fahrenheit, damage wing tissue and even kill dragonflies.
Curiously, the authors did not observe the same trend in female dragonflies. They figure this is because females spend more time resting in the shade, while males tend to aggressively defend territory, zipping around in the hot sun.
The patterns they observed suggest long-term evolution. But what is happening now, in the short-term?
The team looked at photos from 2005 to 2019 and compared how dragonfly wing ornamentation varied with yearly average temperature. In hotter years, male dragonflies had less wing ornamentation. But there was no overall change at the end of the time period.
Moore said the likely reason they observed less wing coloration in warmer years was simple: dragonflies with darker wing spots had already overheated before they were photographed by observers.
There was so much year-to-year variability over the 15-year time period that it isn’t surprising that researchers have not seen a lasting change yet, Moore said.
But this process is likely to play out more frequently as the climate warms, leading to long-term evolution.
“Given the climate warming scenarios that we anticipate over the next 100 years, we’ll eventually see this natural selection we are detecting now, within years, turn into lasting evolutionary change,” he said.
The authors say this has conservation implications.
“Something that I think we need to start thinking about more is how the presence of specific traits might allow certain populations to evolve in response to climate change more than others,” said Kasey Fowler-Finn, associate professor of biology at SLU and an author on this study.
Moore agrees. “We’re starting to consider actual traits that animals and plants have that make them better suited to one type of environment or another,” he said.
Conservationists can use this knowledge for management decisions, and reproduction needs to be considered in conservation policies, Moore said. After all, a species won’t survive if individuals can’t mate.
Outside scientists were encouraged by the study.
“Most of the previous studies have tried to really isolate the thermal function of traits, and this study is nice that it looks at a trait that is also involved in reproduction,” said Lauren Buckley, professor and evolutionary ecologist at the University of Washington.
She suggested an idea for future research: honing in on how dragonflies interact with their environment.
“Dragonflies that are near the water in a local environment are likely to experience the environment very differently than what’s happening in average conditions over the years,” Buckley said. “That would be a suggestion to look at for a next step.”
The tiny insects, which communicate through unusual vibrational signals, still are able to find mates despite rising temperatures.