Male dragonflies lose their color in hot climates to stay cool

In much of the animal kingdom, the males of the species tend to be brightly colored to help attract mates. A new study was recently published led by researcher Michael Moore at Washington University in St. Louis that focused on male dragonflies. Moore found that dragonfly males consistently evolved less breeding coloration in regions with hotter climates.

Moore says the study found that wing pigmentation of dragonfly males evolves consistently in response to the climate, making it among the most predictable evolutionary responses ever observed for mating-related traits. He says that the study reveals that mating-related traits can be just as important to how organisms adapt to their climate as survival-related traits. Many dragonflies have patches of dark pigmentation on the wings used to court mates and intimidate rivals.

However, beyond its function in mating, having dark pigmentation in the wings has been shown to heat dragonflies by as much as two degrees Celsius. Having that extra pigmentation in the wings could cause the dragonfly to overheat in climates that are already hot. The team wanted to see if additional heating might force dragonflies to evolve different amounts of wing pigmentation for different climates. The study created a database of 319 dragonfly species using field guides and citizen-scientist observations.

Participants examined wing ornamentation in photographs submitted to iNaturalist and gathered information about climate variables in locations where the dragonflies were observed. Researchers also directly measured wing pigmentation of individual dragonflies from almost 3000 iNaturalist observations focusing on a group of ten select species. In each of those ten species, dragonflies were evaluated based on how they differed between warm and cooler parts of the geographic range.

Researchers discovered male dragonflies almost always responded to warmer temperatures by evolving less wing pigmentation. Dragonflies spotted in warmer years would have less wing pigmentation than dragonflies of the same species in cooler years based on observations in the database ranging between 2005 and 2019. Interestingly, researchers found that dragonfly females don't show changes in wing coloration based on the climate.