In a new study, researchers at Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, have discovered that the colour of dragonfly communities reacts to seasonal fluctuations in solar radiation. In spring and autumn, dragonflies with darker colour nuances are more likely to fly, while the specimens that appear in summer tend to be lighter in colour. The results of the study have now been published in the journal Nature Communications.
The colour adaptation allows the predatory insects to regulate their body temperature. Dark colours absorb heat better than light colours. It is important to note that it is not individual animals that change their colour, explains Professor Christian Hof. He heads the newly created Chair of Global Change Ecology at JMU: "What changes and adapts to solar radiation, so to speak, is the average coloration of all dragonflies flying at any one time."
Previous research showed that in northern regions, darker-coloured and larger dragonfly species tend to fly, as they are better able to retain heat. Lighter-coloured species, on the other hand, are found in the sunny south, where their coloration protects the animals from overheating.
Colour Change over the Course of the Year Verified for the First Time
The team led by Dr. Roberto Novella-Fernandez and Professor Christian Hof began their work during their time at the Chair of Terrestrial Ecology at the Technische Universität München (TUM) and completed it after moving to JMU together.
For the study, they examined and analysed scientific observation data of dragonfly communities from 1990 to 2020 in the UK. The researchers discovered that the average coloration of dragonflies changes seasonally.
"For the first time, we were able to prove that the average body brightness of dragonflies not only differs between warmer and colder regions, but also that lighter species tend to be found during the course of the year in months with stronger sunlight, i.e. in summer, while darker specimens fly in spring and autumn," explains Roberto Novella-Fernandez, lead author of the study.
Christian Hof adds: "We also see in the evaluated data that this seasonal colour variation has changed in the course of climate change." However, global warming is primarily changing the temperature and not the solar radiation.
"The warming may even be shifting the pattern in a direction that is unfavourable for the dragonflies because they no longer fly under ideal solar radiation conditions. Understanding this in more detail is one of our next goals," continues Novella-Fernandez.
Mechanisms of Colour Change in Insects Offer New Field of Research
In the current study, the researchers, in collaboration with colleagues from the Philipps-Universität Marburg, were able to evaluate the available data on the colour characteristics of dragonflies. "By relating changes in the characteristics of species, such as the coloration of insects, to environmental changes, we can better understand the causes of biodiversity loss. The aim of our research group at TUM, which was funded from 2018 to 2023 as part of the Bavarian Climate Research Network bayklif, was to contribute to this. We want to continue this work at the University of Würzburg," concludes Christian Hof.
