Lighten Up

The size of dragonfly males’ dark wing patches foreshadows their response to climate change. 

Dragonfly with green head, bluish body, and wings angled down, perched with red leaves in background

An adult male blue dasher (Pachydiplax longipennis) perched on a railing in St. Louis, MO.

Michael Moore

Dark markings on dragonfly wings are a sexually selected trait, but a new study shows how these markings vary based on environmental temperature, and how their evolution may allow dragonflies to adapt to warming over the next hundred years.

The darker a dragonfly’s wings are, the more heat it absorbs. For males, darker wings also attract more mates. In one of the first studies to look at climate’s impact on a sexually selected trait, a team of biologists led by Michael Moore of Washington University in St. Louis collected data from field guides and citizen science observations for 319 North American dragonfly species and found that males of species in colder climates have darker wings than those in warmer climates.

They found the same pattern within species, with males in colder areas having darker wings. Using more than 2,700 iNaturalist photos of ten widespread species from a fifteen-year period, the researchers found that within populations, males had darker wings in colder years. Previous research found that individual dragonflies did not develop lighter wings when raised in warmer temperatures, suggesting that adaptive differences between individuals are genetic. This means that natural or sexual selection can affect how light or dark, on average, males’ wings become over time.

Based on current predictions for global temperature increases and observed evolution of similar traits, the researchers calculated how much change in each dragonfly species’ wings markings can be expected by 2070, and whether it will be enough to keep species from going extinct. Their results suggest that male dragonflies’ wing pigmentation will decrease by about 6 percent on average, though some species will lose as much as 26 percent of their wing pigmentation. However, any changes in wing color are likely to be mediated by other pressures if, for example, such changes affect males’ ability to defend territories or find mates. In addition to refining these predictions, Moore said he hopes to further investigate factors affecting female wing coloration, as it does not respond to temperature the same way as male wing coloration. (PNAS

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