Michael Moore at the Living Earth Collaborative and Washington University in Saint Louis, Missouri, and his colleagues, examined hundreds of thousands of records of dragonflies representing 319 North American species and compared them to the animals’ home climates. They found that the cooler the region, the darker and more elaborate was the wing colouration on males of each species.
The team then focused on 10 dragonfly species with a particularly wide geographical range across North America. They examined 2700 photographs of these species uploaded to the iNaturalist community science platform. This revealed that, even within one dragonfly species, males had wings that were less colourful in warmer climates.
This makes sense, because colourful wings absorb more sunlight – and become warmer – than colourless wings. In fact, coloured patterns can raise wing temperatures more than 2 °C, damaging wing tissue, which can even lead to death by overheating.
But this also suggests that, as the climate warms, male dragonflies might stand their best chance of surviving if they have less colourful wings.
“It’s very likely that dragonflies will lose a moderate amount of their wing colouration as they adapt to warmer temperatures associated with climate change,” Moore says. “It becomes a cost-benefit question.”
Finally, the researchers took a closer look at how their 10 focus species have changed in the recent past. They discovered that male dragonflies photographed between 2005 and 2019 tended to have less colourful wings in warmer years and more colourful wings in cooler years. This implies that when it’s hotter, only the less colourful male dragonflies survive.
Female dragonflies have colourful wings too, but they are less likely to lose their colour in hotter years. This may be because females prefer to hide in the shade while males fly in the sunlight.
But it suggests the dragonflies may face problems in future. If colourful females find the blander males less attractive they may refuse to mate with them, Moore says. Worse, the females might begin struggling to recognise males of their own species, and may start mating with males from another species by mistake.
“That happens sometimes already, and the offspring don’t do very well, so that would be a pretty detrimental consequence,” says Moore.
Journal reference: PNAS, DOI: 10.1073/pnas.2101458118
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