A study led by Michael Moore from the Washington University in St. Louis has revealed that male dragonflies have consistently evolved to have less breeding coloration in regions with a hotter climate.
Moore. Image Credit: Washington University in St. Louis.
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.
Michael Moore, Postdoctoral Fellow, Living Earth Collaborative
“This work reveals that mating-related traits can be just as important to how organisms adapt to their climates as survival-related traits,” added Moore.
Several dragonflies consist of patches of dark black pigmentation on their wings, which they use to court prospective mates and intimidate rivals.
“Beyond its function in reproduction, having a lot of dark pigmentation on the wings can heat dragonflies up by as much as 2 degrees Celsius, quite a big shift!. While this pigmentation can help dragonflies find mates, extra heating could also cause them to overheat in places that are already hot,” added Moore, stating that it would approximately be equal to a 3.5 °F change.
The team was interested to know whether the additional heat would force dragonflies to evolve varied wing pigmentation in different climates.
As part of their study, the researchers made a database of 319 dragonfly species with the help of field guides and citizen-scientist observation. The wing ornamentation was assessed using the photographs submitted to iNaturalist and information related to climate variables in the regions in which the dragonflies were observed were collected.
In addition, the team investigated the amount of wing pigmentation on individual dragonflies belonging to nearly 3000 iNaturalist observations in a focused group of 10 selected species. The 10 species of dragonflies were examined based on the variations in their patterns with respect to the cool or warm regions they inhabited.
When the species were compared within or outside the same cooler or warmer regions, the researchers observed that all male dragonflies almost always responded to the warmer temperatures by evolving less wing pigmentation.
In another dimension, male dragonflies in warmer years were found to have less wing pigmentation than the ones belonging to the same species in cooler years (the database included observations from 2005 to 2019).
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.
Michael Moore, Postdoctoral Fellow, Living Earth Collaborative
The research involved predictions, based on climate warming scenarios, which indicate further shrinking of male wing pigmentation will be advantageous as the Earth warms over the next five decades. However, the changes are not the same for both the sexes.
Unlike the males, dragonfly females are not showing any major shifts in how their wing coloration is changing with the current climate. We don’t yet know why males and females are so different, but this does show that we shouldn’t assume that the sexes will adapt to climate change in the same way.
Michael Moore, Postdoctoral Fellow, Living Earth Collaborative
Dragonflies carry different amounts of wing pigments that enable males and females of the same species to identify each other. An interesting thing in the study is that as the male wing pigmentation changes according to the rapid climate change and the female pigmentation evolves due to some other reason, the females might not be able to identify the males of their species.
This could lead to mating with the wrong species.
“Rapid changes in mating-related traits might hinder a species’ ability to identify the correct mate. 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,” concluded Moore.
Journal Reference:
Moore, M. P., et al. (2021) Temperature shapes the costs, benefits and geographic diversification of sexual coloration in a dragonfly. Proceedings of the National Academy of Sciences. doi.org/10.1111/ele.13200.