Male dragonflies lose their 'bling' in hotter climates

They are cooler because they have less pigmentation, but it could make it more difficult to find a partner.The week of July 5, a study by Michael Moore, Washington University in St. Louis, in the Proceedings of the National Academy of Sciences found that dragonfly males consistently have less breeding coloration in hotter regions.Moore is a postdoctoral fellow at Washington University's Living Earth Collaborative. "Our study shows the wing pigmentation in dragonfly males evolves such consistently in response to climate that it's one of the most predictable evolutionary responses ever seen for a mating-related trait," Moore said.He said, "This research reveals that mating-related characteristics can be just as important in how organisms adapt their climates to their environments as survival-related trait."Many dragonflies have dark patches on their wings, which they use to intimidate and court potential mates."Besides its role in reproduction, having lots of dark pigmentation can heat dragonflies up to 2 degrees Celsius. That's quite a significant shift!" Moore noted that this would be roughly equivalent to a 3.5 degree Fahrenheit increase. This pigmentation is important for dragonflies to find their mates. However, they could overheat in hot areas if there is more heating.Researchers were curious to see if additional heating could cause dragonflies different levels of wing pigmentation in different climates.The scientists used citizen-scientist observations and field guides to create a database of 319 species of dragonflies. The scientists examined the wing ornamentation in photos submitted to iNaturalist. They also gathered data about the climate conditions at the locations where they were observed. Researchers also measured individual dragonflies' wing pigmentation using almost 3,000 iNaturalist observations. They focused on 10 species. The scientists also evaluated the differences in populations of each of the 10 species of dragonflies.Researchers compared the occurrence of species in hotter or cooler regions, and compared the populations of species living in warmer or cooler areas. The researchers found the same result: Male dragonflies almost always respond to warmer temperatures by developing less wing pigmentation.The researchers sorted the observations in a different way and found that male dragonflies that were spotted in warmer years had less wing pigmentation (the database contained observations from the period 2005-19).Moore stated that "Given the fact that our planet is likely to continue warming, our results suggest dragonfly males might eventually need to adapt global climate change by changing their wing coloration."Based on climate warming scenarios, projections in the study show that it will be beneficial for male wings pigmentation to shrink further over the next 50 year.However, the changes are not the same for both sexes."Unlike male dragonfly males, female dragonfly wing coloration has not changed significantly in the current climate. Moore stated that while we don't know the reason males and females behave differently, this shows that it is not unreasonable to assume that both sexes will respond in the same manner to climate change.Different amounts of pigment are found on the wings of dragonflies, which help males and women of the same species to identify one another. This research has interesting implications. Females might not recognize males of their species if their male wing pigmentation changes in response to climate change.They could mate with males from the wrong species.Moore stated that rapid changes in mating-related traits could hinder a species’ ability to find the right mate. Moore said that although our research indicates that these pigmentation changes are likely to occur as the world heats, we don't yet know the full extent of the consequences.###This project was done in collaboration with Kim Medley (director of Washington University's Tyson Research Center's environmental field station); Kasey FowlerFinn, associate professor of biology at Saint Louis University; as well as Washington University undergraduates Kaitlyn Harsch, Chanont Sricharoen and Sarah Lee, Caitlin Rice, Paul Rice, and Sophie Kronick.