As global temperatures continue to rise, we find ourselves having to think up creative new ways to keep cool. Maybe you’ve bought a paddling pool or a desk fan, or maybe you’ve developed a penchant for ice lollies at lunch. Dragonflies are no different – they’ve evolved their own unique way of coping with the heat. A new study has found that dragonflies lose their “bling” wing decorations as climates get hotter, and predicts that as the climate crisis worsens, the more the pretty patterns will fade.
Dragonflies have ornamental black patterns on their wings, which vary within and among species and help them to attract a mate. Males with greater pigmentation are typically more successful at this and are better able to scare off rivals. But, unfortunately, when it comes to wing pigmentation, more is not necessarily merrier, as it can heat male dragonflies by up to 2°C (3.6°F), damaging their wing tissue, reducing fighting ability, and even resulting in death by overheating. The evolutionary struggle between natural and sexual selection has been well documented and it seems, in this particular battle, natural selection might just come out on top.
The study, published in the journal Proceedings of the National Academy of Sciences, created a database of 319 dragonfly species and examined wing ornamentation in different species using photographs and known climate information. The researchers also cross-referenced pigmentation of nearly 3,000 dragonflies, from 10 species, with information about their location and climate. They compared how wing color varied among dragonflies of the same species, depending on the climate in which they were born. The database spanned 14 years (2005 to 2019), which allowed the team to track changes in wing pigmentation of the same species over time – male dragonflies spotted in warmer years generally had less wing pigmentation than those of the same species in cooler years.
Whether they compared individuals of the same or different species in different climates, male dragonflies almost always evolved less wing coloration in response to warmer temperatures.
"Our study shows that the wing pigmentation of dragonfly males evolves so consistently in response to the climate that it's among the most predictable evolutionary responses ever observed for a mating-related trait," said lead author Michael Moore in a statement. "Given that our planet is expected to continue warming, our results suggest that dragonfly males may eventually need to adapt to global climate change by evolving less wing coloration."
The team use climate-warming projections, which suggest further reductions in wing pigmentation by 2070. However, there is a disparity between the sexes: “Unlike the males, dragonfly females are not showing any major shifts in how their wing coloration is changing with the current climate,” Moore said. If the ornamentation reduction continues as predicted, this could mean that females no longer recognize males of their own species, and may even mate with males of the wrong species. "Rapid changes in mating-related traits might hinder a species' ability to identify the correct mate," Moore said.
"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."